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Magnetic resonance imaging of the wrist
Foreword The advent of MRI has had an enormous impact on the diagnosis of soft tissue abnormalities of the wrist. Formerly, radiologic diagnosis was dependent on indirect signs such as malposition of bone, or ultimately, on arthrography. The place of MRI in the diagnosis of derangements of the wrist is now undisputed and has become the gold standard for imaging diagnosis. Our authors are recognized authorities in this field and have produced an outstanding primer for members of the radiologic or orthopedic community who work in this arena. I’m certain that our readers will find it worthwhile reading. Theodore
Curr Probl
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E. Keats, M.D. Editor-in-Chief
189
Mark
Anderson,
MD,
ing at the University of California, Davis, Medical Center and a fellowship in MRI at the University of California, San Francisco, Medical Center. He is an associate professor of radiology at the University of Virginia Health Sciences Center in Charlottesville, Virginia.
medical degree from the University of Nebraska College of Medicine. She did her residency training at the University of Nebraska Medical Center. Dr. Kaplan is a professor or radiology and orthopedics at the University of Virginia Health Sciences Center in Charlottesville, Virginia, and is also codirector of the Section of Musculoskeletal Imaging. Robert G. Dussault, MD, received his BA degree from the Jean de Brebeuf College, Montreal, Que. . bet, Canada, and his medical Lb degree from the University of Sherbrooke, Sherbrooke, Quebec, Canada. Dr. Dussault is a professor of radiology and orthopedics at the University of Virginia Health Sciences Center in Charlottesville, Virginia, and is codirector of the Section of Musculoskeletal Imaging. Gregory G. Degnan, MD, received his BA degree from Virginia Wesleyan College in Norfolk, Virginia, and his medical degree from Eastern Virginia Medical School in Norfolk, Virginia. He did his residency training at the naval hospital in Portsmouth, Virginia, and a fellowship in hand and microvascular surgery at Thomas Jefferson Medical College in Philadelphia, Pennsylvania. Dr. Degnan is an assistant professor of surgery at the Uniformed Services University of Health Sciences, Bethesda, Maryland, and is an assistant professor of orthopedic surgery at the University of Virginia Health Sciences Center in Charlottesville, Virginia.
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Magnetic
Resonance
Imaging
Mark W. Anderson,
MD
Phoebe
A. Kaplan,
MD
Robert G. Dussault,
MD
Gregory
G. Degnan,
Wrist abnormalities are often complex and difficult to diagnose.Clinical assessmentcan be extremely challenging, and as a result, diagnostic imaging usually plays a central role in the evaluation of patients with wrist pain. Conventional radiography, radionuclide bone scan, conventional and computed tomography, and arthrographyhave been most often emphasizedin imaging alogrithms for the work-up of patients with wrist pain, with magnetic resonanceimaging (MRI) relegatedto a secondaryrole.lT5This is likely due to a number of factors. The anatomy of the wrist is complex, and the structures of interest are small. Early MR scanslacked the resolutionrequiredto demonstratethe necessarydetail. Even with the technologic advancesavailable today, a lack of sufficient attention to technical details can result in a non-diagnosticscan.Additionally, the radiologist’s understandingof wrist anatomy has had to evolve along with the technology,and many MR findings once consideredpathologic have been shown to representeither normal variants or clinically insignificant findings in asymptomatic individuals. Despite thesechallenges,MRI has clear advantages over other techniques;it is the only imaging examination that simultaneouslydemonstratesboth osseousand soft tissue structures.Maximizing the diagnosticutility of a wrist MR examinationdependson 3 factors:(1) the ability to producehigh-resolutionimages,(2) the developmentof a systematicapproachto image analysis,and (3) a thoroughknowledgeof normal wrist anatomyand the pathologic entities that commonly affect it. The first sectionof this review is a step-by-stepguide describinghow to set up and acquirea high-resolution study.This is followed by a discussionof normal wrist anatomyin the contextof our approachto image analysis. Finally, we will review common types of wrist pathology and offer our thoughtsregardingthe role of MRI in thework-up of a patientwith wrist pain. Our purposeis to providea useful andpracticalguidefor the performanceandinterpretationof MR studiesof the wrist. Curr Probl
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of the Wrist
MD
MRI Technique General
Considerafions
To achieve the spatial resolution necessaryto demonstrate the small structuresof interest, a small field of view (8 to 12 cm), thin slice thickness(1 to 3 mm), and a high imaging matrix (196 to 512) are used.Because each of these factors tends to decreasethe signal-tonoise ratio and overall image quality, a surface coil must be used.6 Numerouscoils areavailablefor wrist imaging. These include dedicatedwrist coils, a flexible (wrap-around) coil, anorbit coil, small circular coils (usuallyin a paired configurationalongthe volar and dorsal surfacesof the wrist), and-in some cases-a standardextremity coil. But not all coils arecapableof generatingthe signal-tonoise ratio and homogeneouspenetrationrequired for optimal imaging, and therefore direct comparison of images from different coils is helpful when selecting equipment.Whichevercoil is used,it shouldbe centered 1 finger-breadthdistal to the ulnar head. Patient Positioning It is of prime importanceto assurethat the patient is in a comfortableposition to minimize motion-relatedartifacts that degradeimage quality. This is most often accomplishedby scanningthe patient in a supineposition with the wrist held at the side. However, if the patient is large,this may not be physically possible.In that case,the patient is placed in a proneposition with the arm held over the head.Paddingplaced at pressure points is essentialfor comfort in this position. Because of the wide rangeof motion at the wrist, careshouldbe takento place the wrist in a neutralposition by aligning the long axesof the radiusand metacarpalswhile minimizing ulnar/radial and dorsal/volarangulation.7Once the patient is in a comfortableposition and satisfactory wrist positioning has been attained,passiverestraints such as sandbags,tape,or foam rubber shouldbe used for maximal immobilization of the wrist. 191
FIG 1. Occult triquetral fracture. Coronal fast spin echo inversion recovery (A) and coronal T2*W (6) images demonstrate high-signal-intensity edema within the triquetrum (arrow) compatible with bone contusion. Note the poor demonstration of marrow edema on the gradient echo image. Note also the low-signal intensity-cartilage contrasted with joint fluid on the inversion recovery image and the similar signal intensities of articular cartilage
TABLE
and
joint
fluid
1. Standard
Imaging
Plane
Coronal Coronal Coronal Axial Axial Sagittal
on the gradient
imaging
Pulse
image
(small
arrows).
protocol
Sequence Tl GRE-T2* FSE-IR Tl GRE-T2* Tl
echo
TR (MSec)
TE (MSec)
450 480 3915 450 600 550
12 18 29 12 18 12
TR, Repetition
time; TE, echo time; TI, inversion
Imaging
Protocol
time; NEX, number
Flip angle 90 30 180 90 30 90 of excitations;
Our basic wrist MRI protocol includes Tl-weighted (TlW), gradient echo T2*-weighted (GRE-T2*W), and fast spin echo inversion recovery (FSE-IR) sequences in the coronal plane. Axial TlW and GRE-T2*W images are also acquired, followed by a sagittal TlW sequence. In cases of suspected mass, infection, or inflammatory arthritis, fat-saturated TlW images are obtained in the coronal and axial planes after the administration of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). Other parameters are shown in Table 1. Pulse Sequences Spin Echo. TlW images are useful for delineating anatomic planes, marrow architecture, fat content in masses, and subacute hemorrhage. The value of T2W imaging is related in large part to the increased signal
192
(degrees)
TI (MSec)
Slice Thickness
150 -
(mm)
3 2 3 3 3 3
Matrix 384x 384x 434x512 384x 384x 384x
NEX
FOV (cm)
1 1 1 1 1 1
10
512 512 512 512 512
10 10 10 10 10
FOV, field of view.
intensity of fluid on these scans, which often highlights pathologic processes. However, we do not include a conventional T2W sequence in our standard protocol because of the suboptimal image quality caused by long acquisition times that result in patient discomfort and motion artifacts. Fast Spin Echo. The fast spin echo (FSE) (also known as turbo spin echo) technique allows for much more rapid acquisition of T2W images because multiple echoes are obtained from each 90-degree pulse, as opposed to a single echo in conventional T2W imaging. This provides several options. Compared with a conventional T2W sequence, the same number of images of equal resolution can be acquired with an FSE sequence in a fraction of the time. Alternatively, images of higher resolution or with an improved signal-tonoise ratio can be obtained by increasing the imaging matrix or number of signal averages, respectively, without increasing the overall imaging time.6
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Despite these advantages, we do not use FSE imaging in the wrist because it also has certain drawbacks. Blurring along tissue margins is common on FSE images, especially with proton density or Tl W sequences. This is most pronounced in tissues with short T2 values,s such as the mensici in the knee, and has resulted in decreased sensitivity in detecting meniscal tears.9 Given the similar histologic structure and MR appearance of the triangular fibrocartilage and intrinsic ligaments, tears of these structures could theoretically be missed as well. The FSE technique is also very gradient intensive, as are the small fields of view and thin slices used in wrist imaging. This refers to the amount of power required by the magnetic gradients, and since this is limited, some type of trade-off is often required with FSE imaging, such as increasing the field of view or slice thickness.6 A final drawback of FSE imaging is the high signal intensity of fat on FSE T2W images. As a result, soft tissue and especially marrow pathology may be obscured because of the similar signal intensity of fat and fluid on these images. This can be overcome by applying a frequency-selective fat-saturation pulse, thereby making any bright signal from fluid or edema very conspicuous against the dark background of suppressed fat. Any heterogeneity in the magnetic field, however, can result in patchy fat saturation that may mimic pathology when none is present. Inversion Recovery. Traditionally, conventional inversion recovery (STIR) sequences suffered from long acquisition times, a limited number of slices, and a poor signal-to-noise ratio. However, these drawbacks have been almost completely overcome with the development of an FSE-IR technique. FSE-IR images are extremely sensitive for detecting soft tissue and marrow pathology (Fig 1). We use this sequence in the coronal plane to assess for bone contusions and occult fractures as well as any fluid collections. Fluid may also be evident within ligament tears or perforations, but the spatial resolution obtained with this sequence is worse than with GRE. Gradient Echo. There are a number of different GRE sequences, but all rely on the use of a gradient reversal to produce the echo rather than the 180-degree pulse used with spin echo sequences. lo (Because of this difference, T2W images obtained with a GRE sequence are designated T2* .) GRE imaging can be performed by using a 2dimensional multislice or a 3-dimensional “volume” technique. The latter provides extremely thin sections
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FIG 2. Axial Tl W image at the level of the scaphoid (SC) and pisiform (P) showing proper orientation of coronal (C) and sagiftal (S) scanning planes.
FIG 3. Coronal Tl W image demonstrating the distal radial ulnar joint (small arrows), radiocarpal joint (R), and midcarpal joint (M). Note also the low-signal-intensity trabeculae coursing through the high-signalintensity marrow fat. TABLE Coronal
Axial
Sagittal
2. Anatomy
of interest
based
on imaging
plane
Osseous architecture Scapholunate ligament Lunotriquetral ligament Triangular fibrocartilage Volar and dorsal radioulnar ligaments Extrinsic ligaments Tendons Median nerve/carpal tunnel Ulnar nerve/Guyon’s canal Distal radioulnar joint Pisotriquetral joint Carpal alignment Pisotriquetral joint Extrinsic ligaments (in cross section)
193
FIG
4.
Normal
coronal
anatomy.
Sequential
radiotriquetral ligament; DRU, dorsal radioulnar cus homolog; P, pisiform; PS, prestyloid recess; ment; S, scaphoid; SLL, scapholunate ligament;
coronal
images
from
volar
(A)
to dorsal
(G).
C, Capitate;
DRUJ,
distal
radioulnar
joint;
DRT, dorsal
ligament; F, flexor tendons: L, lunate; LTL, lunotriquetral ligament; MN, median nerve; MH, menisRCL, radial collateral ligament; RLT, radiolunotriquetral ligament; RSC, radioscaphocapitate ligaTM, trapezium; TD, trapezoid; TFC, triangular fibrocartilage; T, triquetrum; VRU, volar radioulnar
ligament.
(less than 1 mm) and nearly isotropic resolution (equal pixel dimensions in all directions) so that reformatted images can be generated in virtually any plane without a loss of resolution.’ l Because this often requires relatively lengthy imaging times, we prefer the 2-dimensional technique, inasmuch as it is also capable of providing thin
194
slices and exquisite depiction of small structures. Ligaments and articular cartilage are especially well demonstrated with these sequences. We obtain T2*W images in the coronal plane to evaluate the intrinsic and extrinsic ligaments, triangular fibrocartilage, and articular cartilage. Axial T2*W images are useful for evaluat-
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(FIG 4,
continued)
ing tendons, the distal radioulnar joint, the carpal tunnel, and Guyon’s canal. Potential drawbacks of GRE imaging include relatively poor contrast resolution in other soft tissues, increased signal within ligaments and tendons because of the magic angle effect (discussed below), and poor depiction of marrow edema (with high field-strength units) because of susceptibility effects at the interface between cancellous bone and marrow fat (Fig 1). Gd-DTPA. We administer intravenous Gd-DTPA in cases of suspected mass (to separate cystic from solid
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lesions), infection (to identify soft tissue abscesses), or inflammatory arthritis (to better differentiate synovium and pannus from joint fluid). We do not use Gd-DTPA for other routine clinical indications. Enhancement is most conspicuous on TlW images combined with frequency-selective fat-saturation. The use of inn-a-articular gadolinium in the wrist has been described, but it increases both the time and expense of the examination. Although the depiction of intra-articular structures and ligamentous pathology is superb with this technique,12 the added value to conventional MRI of the wrist has been found to be marginal, and its routine use would not justify the added cost and time.13 Imaging Planes. Our standard imaging protocol includes all three conventional planes: coronal, axial, and sagittal. It is important to prescribe the coronal and sagittal images from an axial slice at the level of the pisiform to assure that these images are acquired in true orthogonal planes. Coronal images are obtained parallel to a line joining the volar surfaces of the pisiform and scaphoid bones, and sagittal images are aligned perpendicular to that axis (Fig 2). Coronal images are best for evaluating osseous architecture, the triangular fibrocartilage complex, and the intrinsic and extrinsic ligaments of the wrist. The tendons of the wrist, the carpal tunnel, Guyon’s canal, and the distal radioulnar joint are best visualized in the axial plane. Some centers do not obtain sagittal images, but we find that they are useful for analyzing carpal alignment, the pisotriquetral joint, and the extrinsic ligaments in cross section and for further evaluating abnormalities seen in other planes (Table 2).
195
FIG 5. Normal axial anatomy. Axial T2*W images at ihe level of the distal radioulnar level of the hamate (C, D). C, Capitate; DRUJ, distal radioulnar joint; extensor tendons: extensor carpi radialis longus; . . . digit1 mmlmi; 9, extensor carpi H, hamate; LT, Lister’s tubercle; UNV,
ulnar
Normal
neurovascular
Anatomy
4, extensor
carpi
radialis
brevis;
5, extensor
longus;
6, extensor
digitorum;
7, extensor
indicis;
8, extensor
ulnaris (ECU); FR, flexor retinaculum; F, flexor digitorum tendons: FCR, flexor carpi radialis; KU, flexor carpi MN, median nerve; P, pisiform; RA, radial artery; S, scaphoid; TM, trapezium; TD, trapezoid; T, triquetrum;
ulnaris; U, ulna;
bundle.
(see Figs 3 through
6)
Osseous The head of the distal ulna articulates with the sigmoid notch of the radius, forming the distal radioulnar joint (Fig 3), a pivot joint that allows for a wide range of pronation and supination. A thin layer of articular cartilage is usually seen along the surface of the ulnar head. The distal articular surface of the radius is normally positioned at the same level as the convex surface of the ulnar head on coronal images. Ulna plus or ulna minus variance refers to a more distal or proximal position of the ulna relative to the radius.14 Under norma1 conditions, the radius can shorten 1 to 3 mm with respect to the ulna depending on arm position.15 Lister’s tubercle is a small osseous prominence along the dorsal margin of the distal radius.
196
pollicis
joint (A), pisiform (6) and T2*W and Tl W images at the 1, abductor pollicis longus; 2, extensor pollicis brevis; 3,
The radiocarpal compartment lies between the distal radius and the triangular fibrocartilage proximally and the proximal carpal row distally, which is made up of the scaphoid, lunate, triquetrum, and pisiform (from lateral to medial). The lunate is tightly bound to the scaphoid and triquetrum by interosseous ligaments along their proximal aspects. Both the scaphoid and lunate have tenuous blood supplies, placing them at higher risk for avascular necrosis.16 The triquetrum articulates with the pisiform, a sesamoid of the flexor carpi ulnaris tendon. In at least 40% of wrists, a communication exists between the radiocarpal and pisotriquetral joints.5>17 The pre-styloid recess is a small synovial extension of the radiocarpal compartment along the volar tip of the ulnar styloid. Articular cartilage along the distal radius can be seen to wrap around its ulnar margin at the attachment of the triangular fibrocartilage.
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FIG 6. Normal sagittal anatomy. Sagittal TlW images at the level of the scaphoid (A), lunate (B), and triquetrum (C). C, Capitate; DRT, dorsal radiotriquetral ligament; L, lunate; RLT, radiolunotriquetral ligament; RSC, radioscaphocapitate ligament; S, scaphoid; TFC, triangular fibrocartilage; T, triquetrum; U, ulna.
The mid-carpal compartment extends between the proximal carpal row and distal carpal row, which is composed of the trapezium, trapezoid, capitate, and hamate. This compartment also communicates with the carpal metacarpal joint spaces, usually via the space between the trapezium and trapezoid.5 The capitate is the largest carpal bone, and with the lunate it forms a strong central column that is integral for flexion and extension. Because of marrow fat, the bones normally demonstrate homogeneous high signal intensity on TlW images (with the exception of low signal intensity trabeculae and bone islands [Fig 31) and low signal intensity on FSE-IR images. On GRE-T2”W images, marrow signal intensity depends on the concentration of trabeculae. In areas of abundant trabeculae, which include the carpal bones and distal radius and ulna, marrow signal intensity is quite low because of susceptibility effects at the bone-fat interfaces. Cortical margins are of low signal intensity on all pulse sequences.
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197
FIG 9. Axial Tl W image shows the median nerve (arrows) between the flexor digitorum tendons at a deeper level than
interposed is normally
seen.
FIG 7. Coronal T2*W image shows both limbs of the triangular cartilage (T) attaching to the ulnar styloid with high-signal-intensity sue between them. Note also the normal scapholunate (small and
lunotriquetral
(arrowhead)
intensity cartilage and displaying their substance, a normal variant.
FIG 8. between (arrow].
Coronal T2*W the triangular
ligaments intermediate
image demonstrates fibrocartilage (7’)
attaching signal
to
high-signal-
intensity
the pre-styloid and meniscus
fibrotisarrow) within
recess (P) homolog
Carti/age/Synovium Thin layers of articular cartilage are normally visible on coronal images along the ulnar head and distal radius
198
FIG lunate
10.
Carpal
related
the capitate
alignment. to positioning
(C) and
lunate
Sagittal
Tl W image
of the wrist (I) remain
in slight colinear.
reveals dorsi
dorsal flexion.
F, Flexor
tilt of the Note
that
tendons.
(including along its ulnar margin at the attachment of the triangular fibrocartilage) and around most surfaces of the carpal bones. Normal cartilage is bright on GRE-T2*W
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FIG 11. Magic angle effect. Axial TlW (A) demonstrate homogeneous intermediate signal
and T2’W (B) images intensity within the ten-
dons on the Tl W image, which partially resolves on the gradient echo image. The involvement of multiple tendons and lack of tendon enlargement
or surrounding
fluid
also argue
against
true
pathology.
images. It is easily distinguished from dark subchondral bone, but it can be difficult to separate from joint fluid on these images (Fig 1). Cartilage is of moderately low signal intensity on FSE-IR and fat-saturated FSE-T2W images, resulting in striking contrast with the high signal intensity of joint fluid (Fig 1). Even so, subtle cartilage defects are difficult to identify on MR images because the articular cartilage is so thin in the wrist. Normal synoviurn is not visible on MR images. ligamenfs Wrist stability is maintained primarily through ligamentous support. The ligaments of the wrist are divided into intrinsic and extrinsic groups. Intrinsic Ligaments. The intrinsic carpal ligaments extend between the carpal bones and are important for maintaining wrist stability by limiting osseous motion. The scapholunate ligament (SLL) and lunotriquetral ligament (LTL) are clinically the most important and can be routinely demonstrated on high-resolution coronal MR images. The SLL is a C-shaped, band-like structure that joins the medial aspect of the proximal pole of the scaphoid to the lateral aspect of the lunate.18 Three distinct por-
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FIG 12. Accessory extensor digitorum
muscle. Axial Tl (A) and T2 (B) images brevis manus muscle [arrows) surrounding
sor tendon of the index finger (open neous signal intensity, which parallels
arrow). Note its relative that of skeletal muscle.
reveal an the extenhomoge-
tions have been described: dorsal, middle, and v01ar.~~ The dorsal and volar segments are the strongest and most important for maintaining stability at the scapholunate articulation.20 The middle portion is relatively thin, and asymptomatic perforations of this segment are common. 21 On high-resolution GRE coronal images, the volar portion of the SLL is trapezoidal in shape, and its signal intensity is typically higher than that of the middle and dorsal segments, presumably because of the looser connective tissue in this portion. The middle segment displays a triangular shape. The band-like dorsal segment is of low signal intensity owing to densely arranged collagen fibers. 22 Each portion of the ligament may attach to bone or cartilage, and the specific pattern of attachment varies from patient to patient.22 The LTL links the proximal, ulnar aspect of the lunate with the adjacent proximal radial aspect of the triquetrum. It is smaller than the SLL, measuring only 2 mm in thickness, and consequently was less consistently demonstrated with early MR techniques.23 However, it is routinely depicted on high-resolution GRE coronal
199
FIG 13. images zoid
Occult bone contusion. Axial Tl reveal abnormal, edema-like signal
(arrows)
compatible
with
a bone
(A)
and coronal intensity within
T2”W (B) the trape-
contusion.
images. In most cases it is a linear or delta-shaped band of homogenous low signal intensity.23 Intermediate signal intensity may extend partly or completely across the SLL or LTL in asymptomatic patients. 23,24Ligament tears or perforations can display a similar appearance on Tl proton density and some GRE sequences but should demonstrate high signal intensity that is equal to that of fluid on T2W or T2*W images. Extrinsic Ligaments. The extrinsic carpal ligaments course obliquely across the volar and dorsal surfaces of the wrist and attach the cat-pus to the forearm. The MR appearances of the extrinsic ligaments have been extensively described in the literature. 12,25-30These intracapsular, extra-synovial structures assist in maintaining wrist stability and appear as striated, band-like struc-
200
tures of alternating low and intermediate signal intensity on coronal GRE images. They are displayed in cross section on sagittal images.29 The primary volar ligaments include the radioscaphocapitate, radiolunotriquetral (also known as the long radiolunate), and short radiolunate ligaments.31 These are stronger and more important stabilizers than the extrinsic ligaments on the dorsum of the wrist. The radioscaphocapitate ligament extends from the radial styloid, across the waist of the scaphoid to attach to the capitate. The fibers that course from the most-distal aspect of the radial styloid to the tubercle of the scaphoid have been described as the radial collateral ligament.31 The radiolunotriquetral ligament is the largest and strongest ligament of the wrist.32 It also originates from the radial styloid process, just ulnar to the radioscaphocapitate ligament, and then follows a more horizontal course with attachments to the lunate and triquetrum. The short radiolunate ligament arises from the volar surface of the radius at the level of the lunate and extends to its volar surface.31 The major dorsal extrinsic ligament, the radiotriquen-al ligament (or dorsal radiocarpal ligament), is a thickening of the dorsal wrist capsule. It originates from the ulnar aspect of Lister’s tubercle and attaches to the dorsal surfaces of the scaphoid, lunate, and triquetrum.31~33 These structures are often difficult to identify, even with thin-section imaging. Because of their oblique orientation, they are virtually never seen in their entirety on one image. Three-dimensional GRE imaging has been advocated for depicting these structures via reformatted images in specialized planes.27>28We do not use this technique because of the extra time involved and because the status of the individual extrinsic ligaments is not of clinical importance to our orthopedic hand surgeon. Triangular Fibrocarthge Complex The triangular fibrocartilage complex is composed of several soft tissue structures along the ulnar aspect of the wrist: the triangular fibrocartilage, the volar and dorsal radioulnar ligaments, the meniscus homolog, the ulnocarpal ligaments, the ulnar collateral ligament, and the sheath of the extensor carpi ulnar-is (ECU) tendon.34,35 It is best seen on coronal images and has 3 major functions: (1) cushioning axial forces across the ulnar carpal region, (2) stabilizing the ulnar carpus, and (3) stabilizing the distal radioulnar joint (DRUJ).34 The triangular tibrocartilage (TFC) extends from a broad attachment along the ulnar margin of the distal radius to the ulnar styloid. The thickness of the TFC has
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FIG 14. Occult distal in more-diffuse edema
radial fracture. Coronal in the distal radius.
FIG 15. Occult scaphoid distal pole of the scaphoid
(A)
Tl
fracture. Coronal Tl W with associated edema.
and inversion
(A) Note
recovery
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demonstrate
a curvilinear
a non-displaced and coronal T2’W (8) images demonstrate also the small perforation within the triangular fibrocartilage
been found to be inversely proportional to the degree of ulnar variance.36 That is, the TFC tends to be thinner in patients with positive ulnar variance and thicker in those with negative ulnar variance. On coronal images the TFC appears as a bow-tie-shaped structure of relatively
Curr
(B) images
fracture
line (small
curvilinear (small
fracture
arrows)
with-
line at the
arrow).
low intensity with or without patchy areas of intermediate signal intensity. 35 The high signal intensity hyaline cartilage at its radial attachment should not be confused with a tear. The TFC often attaches to the ulnar styloid via two striated bands, one inserting at the base of the
201
FIG
16.
the hook
FIG
17.
Twenty-three-year-old
baseball
of the hamate
The corresponding
(arrow).
Twenty-nine-year-old
nal T2*W (B) images demonstrate pole of the scaphoid as evidenced patible
with
man with
player
with occult
triquetral
axial
hamate T2”W
fracture
fracture.
image
and
Tl W image
scaphoid
fracture
(A)
d emonstrates
the high-signal-intensity
complicated
abnormally fracture
by avascular
necrosis.
low signal
intensity
line at this site (curved
Coronal
Tl W
(A)
within arrow).
and
coro-
a small avulsion fracture involving the proximal triquetrium (curved arrows) as well as a fracture of the proximal by a slight cortical step-off (short arrow). The low signal intensity within the proximal pole on both imuges is com-
AVN.
styloid and the other near its tip (Fig 7). Loose areolar tissue between these bands produces intermediate signal intensity that also mimics pathology.35 As with the intrinsic ligaments, a true tear or perforation should be diagnosed only when the traversing signal is equal to that of fluid on T2W or T2*W images. The volar and dorsal radioulnar ligaments are bandlike condensations along the margins of the TFC that function to stabilize the DRUJ.37 These striated bands are consistently seen on coronal images along the most palmar and dorsal aspects of the TFC35 and can be differentiated from it by recognizing that they attach directly to the radius rather than to the articular cartilage. The dorsal ligament blends with the dorsal wrist capsule and sheath of the extensor carpi ulnaris tendon. The volar ligament blends with the volar ulnocarpal (ulnolunate and ulnotriquetral) ligaments that help stabilize the ulnar aspect of the wrist.38 These two ligaments are even less consistent-
202
Axial
(B) demonstrates
ly demonstrated on MR images than are other extrinsic ligaments, and they often appear as a single, intermediate signal intensity sheet of tissue extending from the volar radioulnar ligament to the volar surfaces of the lunate and triquetrum.35 The meniscus homolog is a longitudinally oriented thickening of the capsule extending from the ulnar styloid to the triquetrum. The prestyloid recess is located between the meniscus homolog and TFC and demonstrates a variable amount of volar extension (Fig 8).34 The meniscus homolog is not present in all patients and therefore may not always be seen, even on high-resolution images.35 The extensor carpi ulnaris tendon provides support along the ulnar aspect of the wrist and is best evaluated on axial images. The ulnar collateral ligament, which extends from the ulnar styloid to the triquetrum, is more of a thickening of the capsule than a discrete structure, and it has little mechanical strength.z5>39
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Tendons The tendons of the wrist are best depicted in the axial plane. The extensor tendons are stabilized along the dorsum of the wrist by the extensor retinaculum, a band-like thickening of the antibrachial fascia that courses from the distal forearm to the bases of the metacarpals. 4o Septa extending from the superficial to the deep layers of the fascia form 6 dorsal compartments that contain the extensor tendons. The first dorsal compartment, along the radial border of the distal radius, contains the abductor pollicis longus and extensor pollicis brevis tendons. The second dorsal compartment holds the extensor carpi radialis longus and brevis tendons and is separated from the extensor pollicis longus tendon in the third dorsal compartment by Lister’s tubercle. The extensor digitorum and extensor indicis tendons lie in the fourth compartment. The fifth dorsal compartment contains the extensor digiti minimi tendon, and the extensor carpi ulnaris tendon is found in the sixth compartment. Nine flexor tendons of the wrist lie within 3 common synovial sheaths that travel through the carpal tunnel.16 The flexor digitorum profundus tendons lie deep to those of the flexor digitorum superficialis. The flexor car-pi radialis tendon courses along the radial aspect of the tunnel and can be consistently identified in a shallow groove along the ulnar margin of the trapezium. The flexor car-pi ulnaris tendon lies along the superficial, volar aspect of the wrist and inserts on the pisiform, with some fibers continuing distally to insert on the hamate and fifth metacarpal. The ulnar vessels and nerve are seen just deep to this tendon.
Carpal Tunnel The carpal tunnel is the fibro-osseous space found along the concave volar aspects of the carpal bones.16 It contains the flexor tendons described above and the median nerve. The palmar aspect of the tunnel is bounded by the flexor retinaculum, a dense fibrous band that extends from the scaphoid to the pisiform proximally and from the tubercle of the trapezium to the hook of the hamate distally. The retinaculum normally demonstrates slight palmar bowing.41 There is normally very little fat within the carpal tunnel, but when it is present, it lies dorsal to the flexor tendons. Nerves The median nerve typically lies within the volar, radial aspect of the carpal tunnel just deep to the retinaculum, although its position and shape vary with wrist position
Curr Probl
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1998
FIG 18. saturated, mid-scaphoid abnormality row
edema
Ununited scaphoid fracture. Coronal Tl W (A) and coronal fast spin echo T2W (B) images reveal a fracture through with edema along the distal fracture throughout the proximal pole is consistent versus
ischemic
fatthe
margin. Signal with bone mar-
change.
(Fig 9):2 The nerve demonstrates slightly higher signal intensity than muscle or tendon on TlW images because of its fat content and, as a result, it is usually easy to identify among the low signal intensity tendons. A stippled appearance on axial images reflects the longitudinally oriented fascicles of high signal intensity neuronal fibers that are enclosed in the lower signal
203
intensity perineurium and epineurium.43 The median nerve is oval proximal to and within the carpal tunnel but slightly flattens at the level of pisiform. It normally maintains its size or becomes progressively smaller as it courses through the carpal tunneL41 The ulnar nerve and artery course through Guyon’s canal along the lateral aspect of the pisiform. The floor of the canal is formed by the flexor retinaculum and hypothenar musculature and its roof is formed by a fascial layer that is a distal extension of the antibrachial fascia.44 The ulnar artery lies lateral to the nerve and just superficial to the flexor retinaculum.45 Imaging
Pitfalls
Carpal
Alignment
The alignment of the carpal bones on sag&al images depends on wrist position (Fig 10). The lunate tends to volarflex and dorsiflex relative to the radius when the wrist is placed in radial and ulnar deviation, respectively.46 This highlights the need for careful positioning of the wrist in a neutral position. If needed, the carpal angles can be measured on sequential sagittal scans, analogous to a lateral view of the wrist. Tendons FIG coronal images oatible
19.
AVN
of the
lunate
(Kienbijck’s
disease).
Sagittal
204
(A),
TlW (B), and coronal fat-saturated, fast spin echo TZW (C) demonstrate diffusely abnormal signal within the lunate comwith AVN. Small foci of increased sianal intensitv on T2W imaae I
suggest
Tl W
areas
of revascularization.
Normal variations in the appearance of the wrist tendons may simulate pathology. Spuriously increased signal intensity may occur within tendons because of the magic angle effect. This is related to the orientation of the collagen bundles within the tendon and occurs on
Curr
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Diagn
Radiol,
November/December
1998
images obtained with a short TE (Tl, proton density, and most GRE sequences) when the tendon lies at an angle near 55 degrees to the main magnetic field.47 This increased signal disappears on long TE (T2W) images, which allows for differentiation from true tendon pathology (Fig 11). The magic angle effect may occur in any tendon, depending on the patient’s arm position, and is commonly seen in the extensor pollicis longus because of its oblique course. Increased signal is also commonly present in the extensor carpi ulnaris tendon, although its exact etiology is unknown.48 Another potential pitfall is related to the multiple tendinous slips of the abductor pollicis longus that may be mistaken for longitudinal tears. 48 In each case, these normal variants should be distinguished from true tendon pathology by the lack of tendon enlargement, surrounding fluid and/or peritendinous edema. Anomalous
Muscles
Anomalous muscles are relatively common in the hand and wrist, particularly the accessory palmaris longus muscle. 4g This muscle is identified along the volar soft tissues of the wrist, superficial to the flexor digitorum tendons and medial to the flexor carpi radialis tendon.50 Another anomalous muscle, the extensor digitorium manus brevis muscle, is found on the dorsum of the wrist along the ulnar side of the extensor indicis tendon (Fig 12).51 An anomalous muscle can present as a soft tissue mass, or it may compress the median or ulnar nerve, depending on its location.52 These demonstrate a
Curr
Probl
Diagn
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November/December
1998
FIG 20. Focal AVN. Coronal TlW (A) and fast spin echo inversion recovery (B) images demonstrate abnormal signal within the lunate that is shown to involve the dorsal half of the bone on the sagittal Tl W image (C)(arrow). The increased signal intensity patible with an earlier stage of the disease digitorum tendons.
on the FSE-IR image or revascularization.
is comF, Flexor
205
FIG 21. Capitate fracture with associated AVN. Coronal Tl W (A) and T2*W (B) rma g es d emonstrate mal capitate compatible with AVN and collapse of the proximal articular surface. Fluid is seen extending tion of the capitate
FIG 22. Ulnolunate gular fibrocartilage
on the T2*W
image
impaction syndrome. (curved arrow), and
signal
intensity
wrtnm
bone
tne proxr-
and central
por-
(arrowheads).
Coronal subchondral
positive ulnar Tl W (A) and T2*W (B) tma g es d emonstrate cystic changes in the adjacent lunate (small arrows).
homogeneous MR appearance and follow muscle intensity on all sequences, features that help to differentiate an anomalous muscle from other soft tissue masses.50
TFC and Ligaments The high signal intensity of the hyaline cartilage along the radial attachment of the TFC should not be misinterpreted as a tear or detachment (Fig 4, C and D).
206
abnormal
into the subchondral
variance,
a perforation
of the trian-
Similarly, the intermediate signal intensity of the loose areolar tissue between its two ulnar limbs should be distinguished from a tear, which will display fluid signal intensity on T2W images (Fig 7).48 Heterogeneous, intermediate signal intensity secondary to myxoid degeneration may be seen within the TFC as well as the scapholunate and lunotriquetral ligaments (Fig 4, C, Fig 7). This should not be diagnosed
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG 24. Stretched scapholunate ligament. Coronol T2*W demonstrates widening of the scapholunate interval (arrows) intact but stretched and attenuated scapholunate ligament.
FIG
23.
lntraosseous
images demonstrate scapholunate ligament along vidual
ganglion.
Axial
(A)
a dorsal ganglion cyst as well as an associated
and
coronal
(G) at the intraosseous
the radial aspect of the lunate (arrowhead). fasicles within the median nerve (arrow].
Note
(B)
T2*W
level of the component also
the indi-
as a tear unless the signal intensity is equal to fluid on T2W or GRE images. Similarly, the high signal intensity where portions of the scapholunate and lunotriquetral ligaments attach to articular cartilage rather than directly to bone should not be misinterpreted as tears (Fig 4, D and E, Fig 7).t1 Osseous
Pathology
Physeal
injuries
Injuries to the skeletally immature wrist may lead to abnormalities of the growth plate, metaphysis or epiph-
Curr
Probl
Diagn
Radiol,
November/December
1998
image with an
ysis of the distal radius and ulna. Trauma to the physis (growth plate) can result in the formation of an osseous or fibrous bridge across the physis or slowing of growth in a portion of the physis, both of which can result in growth disturbance. 53 Extension of the injury to the metaphysis may result in a bone contusion or vertically oriented fracture. This may lead to thickening of the growth plate initially, with persistent cartilagenous foci found later within the metaphysis. These different findings have been described in competitive gymnasts.54>55 Physeal injuries can sometimes be detected on conventional radiographs. 56 However, MRI will demonstrate occult fractures and contusions as well as the presence of a bone or fibrous bridge. GRE-T2*W images demonstrate the low-intensitv d osseous or fibrous bridge against the high-signal-intensity cartilage of the physis. GRE sequences can also confirm the cartilagenous nature of the post-traumatic metaphyseal lucencies.54>55 Occult Bone Injuries Radiographically occult bone injuries are common causes of wrist pain. In a patient with recent wrist trauma and negative radiographs, a radionuclide bone scan is recommended as the next step in many imaging algorithms. Although it is extremely sensitive for detecting osseous injuries, bone scintigraphy suffers from a lack of specificity, poor spatial resolution, exposure to ionizing radiation, long examination time (3 to 4 h), and the possibility of a false/negative scan in the acute setting (less than 48 h).57
207
FIG
(A)
Scapholunate and sag&al
scapholunate
ligament
T2”W
25.
ligament tear Tl W (B) images with
widening tear
(arrowhead). Note also the large (arrow). A DISI pattern is seen on lunate
(L). F, Flexor
with DlSl deformity. Coronal demonstrate disruption of the of the scapholunate interval of the triangular fibrocartilage
the sagittal
view
with
dorsal
tilt of the
tendons.
MRl is at least as sensitive as bone scintigraphy for detecting occult osseous injuries58 and offers the additional advantages of excellent spatial resolution with direct demonstration of associated soft tissue injuries, a lack of ionizing radiation, and a short examination time. The cost of MRI has been considered a disadvantage. However, because of its exquisite contrast and spatial resolution, even a limited imaging protocol is highly accurate for detecting osseous injuries.59 In cases of suspected occult osseous injury, we employ a limited “trauma screening” wrist protocol consisting of coronal Tl and FSE-IR sequences that can be offered at a substantially lower charge than a bone scan or standard MR examination. Bone contusions and fractures in the wrist produce typical signal abnormalities in the marrow. A contusion appears as an amorphous, geographic area of abnormal signal intensity. The associated hemorrhage and edema is of low signal intensity on TlW images and high signal intensity on T2W images (Fig 13).60 These changes are especially conspicuous on FSE-IR and fat-saturated FSE-T2W images. 61 An occult fracture is identified as a linear focus of signal abnormality within the marrow edema that is low signal intensity on TlW images and may be either of low or high signal intensity on any type of T2W image (Fig 14).
208
The scaphoid is the most commonly fractured carpal bone and is the second most common wrist fracture after injuries to the distal radius. 62 Early detection and appropriate treatment of a scaphoid fracture is critical because of the relatively high incidence of associated complications that include delayed fracture union or nonunion and avascular necrosis (AVN) of the proximal fragment.63 An average of 16% of scaphoid fractures are not seen on initial radiographs. 64 Accordingly, in most cases of suspected scaphoid fractures, if initial films are negative, the patient is placed in a splint and follow-up radiographs are obtained in 1 to 2 weeks. This results in additional costs related to the follow-up visit and time off of work, and in most series only 15% to 25% of these patients are found to have a proven fracture on follow-up radiographs.64 MRI is highly accurate in detecting and delineating fractures of the scaphoid63,64 and other ossesous structures of the wrist (Figs 15, 16).65 In most cases a frac-
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG 27. SLAC the scapholunate
wrist. Coronal T2*W image demonstrates disruption of ligament with proximal migration of the capitate and
loss of articular cartilage in the radiocarpal space also the attenuation of the triangular fibrocartilage loss of articular
FIG
26.
Scaphoid
fracture
with
associated
DISI
deformity.
Sag&al
Tl W images (A, B) demonstrate non-united scaphoid fracture (arrow). The adjacent sagittal image demonstrates volar translation and dorsal tilt of the lunate (L) compatible with the DISI pattern. F, Flexor tendons;
P, proximal
pole;
D, distal
pole.
ture line will be evident, but cases of diffuse edema without a fracture line have been reported in patients who were shown to have a true scaphoid fracture on
C&rr Probl
Diagn
Radiol,
November/December
1998
FIG
28.
cartilage
Kienbock’s
in the distal
disease
with
radioulnar
VP3
pattern.
(small arrows). (open arrow) joint
Note and
(arrowhead).
Sagitta(
TlW
image
demonstrates diffuse low signal intensity within the lunate (L) consistent with AVN. Note the dorsal displacement and volar tilt of the lunate and volar displacement of the capitate relative to the radius.
follow-up radiographs. 63 With healing, the marrow signal abnormality tends to fade and becomes isointense with adjacent marrow fat.@
209
gical planning. This has been accomplished with varying degrees of success by using radiographs, tomography, bone scan, and intraoperative inspection for punctate bleeding in the viable bone.67 Normal marrow signal intensity on TlW images is highly predictive of viability.68>69 Conversely, low signal intensity on TlW and T2W images is a specific sign of necrosis (Fig 17).68 The pattern of low signal intensity on T 1W images and high signal intensity on T2W images is less specific because it could be related to traumatic bone marrow edema or ischemic change (Fig 18).
FIG
29.
Triangular
fibrocartilage
perforation.
Coronal
demonstrates a small perforation in the triangular cent to its radial attachment (arrow).
FIG
30.
Partial
tear
of the triangular
image demonstrates increased extending into the undersurface
arrow)
without
evidence
fibrocartilage.
signal intensity of the triangular
of a full-thickness
T2*W
fibrocartilage
Coronal
equal to that fibrocartilage
image adia-
T2’W of fluid
(curved
tear.
AVN Because of the tenuous blood supply of the proximal pole of the scaphoid, AVN is a common fracture complication and is often an important contributory factor in the development of nonunion. Assessment of the viability of the proximal fragment is important for sur-
210
Kienbiick’s Disease The exact etiology of AVN of the lunate (Kienbock’s disease) is uncertain, but possible factors include repetitive trauma, acute fracture, lunate geometry, variations in lunate vascular&y, and ulnar minus variance (which results in increased shear forces on the lunate).70,71 This disorder affects men much more commonly than women. The patient typically describes wrist pain that worsens with activity and improves, at least temporarily, with rest. More than 95% of affected patients are involved in manual labor.72 Several anatomic features of the lunate make it especially vulnerable to the development of AVN. Its blood supply is extremely tenuous, with small nutrient arteries entering at only two sites along its dorsal and volar surfaces.73 Limited arterial anastomoses within the lunate result in much of its proximal and distal poles being fed by end arteries. Additionally, its central position in the carpus subjects it to high compressive forces that are even more pronounced when there is negative ulnar variance.r6 Kienbock’s disease follows a predictable sequence. Initially, the osseous changes are confined to the lunate. With progression, lunate fragmentation and collapse occur, ultimately leading to scapholunate dissociation, proximal migration of the capitate, and the development of diffuse degenerative changes.74 Treatment is based on the stage of the disease. Therefore, if the disease is detected at an earlier stage, therapy can then be aimed at preventing lunate collapse and subsequent degeneration and instability.69 Unfortunately, the disease is often clinically silent in its early stages, apparently because of a relative paucity of nerve endings along the lunate, and radiographic changes may not be detected until relatively late in the process, when the damage is irreversible.75>76 Four radiographic stages have been described. Stage I: Normal radiographs. Stage II: Increased density in the
Curr Probl
Diagn
Radiol,
November/December
1998
FIG 3 1. Injuries to the ulnar aspect of the triangular fibrocartilage and adjacent extensor carpi ulnaris tendon sheath. Coronal (A) and axial (6) T2*W images reveal disruption of the triangular fibrocartilage at its ulnar attachment (arrow) with associated extensor carpi ulnaris tendonopathy and probable tendon sheath disruption (arrowhead). E, ECU tendon; U, ulnar styloid.
lunate. Stage III: Lunate collapse, without (IIIA) or with (IIIB) fixed scaphoid rotation and scapholunate dissociation. Stage IV: Generalized carpal degeneration.74 MRI is the most-sensitive imaging modality for detecting osteonecrosis and is more specific than bone scintigraphy. Abnormal marrow signal intensity is present on MR images in stage I disease. Decreased signal intensity on TlW and T2W images is diagnostic (Fig 19).76-78 Increased signal intensity on T2W images suggests an earlier stage of the disease.78 Typically the entire lunate is involved; however, focal
Curr Probl
Diagn
Radio&
November/December
1998
FIG 32. Thirty-nine-year-old man with distal radial fracture, dorsal subluxation of the distal radioulnar joint, and tendonopathy or partial tears of the extensor carpi ulnaris tendon. Axial T2*W images demonstrate disruption of the volar radioulnar ligament (curved arrow) and associated subluxation of the distal radioulnar joint (D). Note also the subluxation and partial tear/tendonopathy of the extensor carpi ulnaris tendon at the level of the distal ulna [arrow) and proximal carpal row (open arrow), as well as fluid surrounding the extensor carpi radialis tendons (arrowheads) that is compatible with tenosynovitis.
AVN can occur (Fig 20). To avoid over-reading small, non-necrotic foci within the bone as AVN, some people believe that AVN should not be diagnosed unless at least one half of the bone is involved.76 Favorable MRI signs suggesting revascularization include diffuse or focal increased signal intensity on T2W images as well as restoration of normal marrow signal intensity overall. Patients with these signs tend to have more-favorable outcomes after surgery.78 AVN can rarely involve other carpal bones and may occur from prior trauma, steroid use, or on an idiopathic basis (Fig 21).7g
211
FIG rum
33. Flexor digitorum tendons in the carpal
FIG
34.
Twentyeight-year-old
donopathy the flexor
involving digitorum
FIG
Thirty-three-year-old
35.
tenosynovitis. tunnel (open
man
Axial
arrows)
with
wrist
the extensor carpi ulnaris tendons in B is compatible
man
with
distal
Tl W (A) and fast spin echo compatible with tenosynovitis.
pain
(arrow) with
radial
after
injury.
Axial
and extensor mild tenosynovitis.
fracture
and
T2*W (B) images demonstrate diffuse edema within the distal radius the abductor pollicis longus and extensor pollicis brevis tendons with
212
TlW
T2W (B) axial images demonstrate (Same patient as in Fig 49.)
(A)
and
T2*W
(B) images
digiti minimi (open arrow) Note also the enlarged
associated
tendonopathy
fluid
reveal
tendons. Slightly median nerve.
of the first
that is compatible with the patient’s peritendinous edema (arrows).
Curr
Probl
dorsal known
Diagn
surrounding
partial
tears
increased
compartment. fracture
Radiol,
the flexor
and/or
signal
Axial
digito-
severe
intensity
Tl W
ten-
around
(A)
and
as well as ill definition
November/December
1998
of
FIG 36. De Quervain’s tenosynovitis. saturated TlW axial (B) and coronal
Axial
TlW
(C)
images
image obtained
(A)
and
fat-
after
the
administration of intravenous gadolinium demonstrate thickening and striking enhancement of the tendon sheaths of the abductor pollicis longus and extensor pollicis brevis tendons (open arrows).
strate associated TFC pathology. MRI is advantageous as compared with other imaging techniques because it provides early evidence of the syndrome by demonstrating signal abnormality in the subchondral marrow of the lunate and/or head of the ulna before radiographic changes are apparent (Fig 22).80 MRI also allows for simultaneous, noninvasive evaluation of the TFC. lntraosseous
Ulnar impaction The ulnar impaction syndrome is the result of chronic abutment of the distal ulna on the lunate, causing cartilage loss, degenerative subchondral bone changes, and tears of the intervening TFC.*O There is a strong relationship between the ulnar impaction syndrome and ulna plus variance because of the increased forces transmitted across the ulnar aspect of the joint with that anatomic configuration. Positive ulnar variance occurs as an anatomic variant or may develop as a result of an impacted radial fracture. Ulna plus variance and changes of the ulnolunate impaction syndrome can be diagnosed on postero-anterior radiographs, but associated subchondral lucencies in the lunate and ulnar head are not evident radiographically until late in the process. Arthrography can demon-
Curr
Probl
Diagn
Radiol,
November/December
1998
Ganglia
Intraosseous ganglia are focal cystic lesions within subchondral bone that are composed of a dense fibrous wall and mucoid fluid. They may occur purely within the bone or result from the intraosseous extension of a soft tissue ganglion cyst. 81 Once thought to be rare, these were found to be responsible for chronic wrist pain in 4% of patients in a large series.82 MR imaging can demonstrate radiographically occult intraosseous ganglia. These appear as well-circumscribed foci of low signal intensity on TlW images and high signal intensity on T2W images of any kind (Fig 23). If other causes of wrist pain such as carpal instability, intraosseous ligament tear, or TFC pathology have been ruled out, a radionuclide bone scan can provide supportive evidence of a symptomatic ganglion if abnormal uptake is identified at the site of the cystic lesion.82
213
FIG T2*W tendon
37.
Extensor
(B) images with mild
presented
with
carpi
ulnaris
demonstrate associated
painful
tendon
subluxation.
subluxation tenosynovitis
clicking
in the wrist
Axial
Tl W
(A)
and
of the extensor carpi ulnaris (arrows) in this patient who after
trauma. FIG
Ligamentous
Pathology
Biomechanics The proximal carpal row functions as an intercalated segment between the distal radius and distal carpal row. l9 These segments are connected and stabilized by ligamentous structures. Without this ligamentous support, the geometry of the carpal bones would lead to a zigzag pattern of collapse during axial loading of the wrist. The scaphoid forms a bridge between the proximal and distal carpal rows and thereby plays an important role in carpal stability.19 The natural tendency of the lunate to dorsiflex under an axial load is countered by its attachment to the scaphoid (which tends to palmarflex) via the SLL. Similarly, the tendency of the triquetrum to dorsiflex is countered by its attachment to the lunate (and scapholunate unit) via the LTL.t9 Carpal instability is defined as a loss of the normal alignment of the carpal bones, and it occurs when there is disruption of these ligamentous
214
38.
injury carpal median proximal
Fifty-one-year-old
2 weeks previously. tunnel demonstrates
woman
with
persistent
wrist
pain
after
Axial T2*W image (A) just proximal to the increased signal intensity within an enlarged
nerve (curved arrow). An axial Tl W image at the level of the carpal tunnel (B) reveals signal abnormality within the tri-
quetrum (I’) compatible with contusion and/or occult ment of the median nerve (curved arrow), and bowing naculum,
compatible
with
post-traumatic
median
nerve
fracture, enlargeof the flexor retineuritis,
constraints.83 Ultimately, carpal instability can lead to carpal collapse and early degenerative changes.t9 Imaging A conventional radiograph should be the first imaging study performed in patients with suspected carpal instability. Stress views and/or video fluoroscopy may reveal an instability pattern that may not be present on routine images. 84 Ligamentous perforation or rupture can be identified with arthrography when abnormal communication of contrast is identified between compartments. However, the exact site of the perforation may be difficult to determine and the clinical significance of an
Curr
Probl
Diagn
Radiol,
November/December
1998
arthrographic abnormality is often uncertain because of the frequency of asymptomatic perforations.85 MRI is a useful adjunct to conventional radiographs because of its ability to directly display the intrinsic and extrinsic ligaments and to identify which segments of the ligaments are abnormal. The most reliable MRI sign of ligamentous disruption is a discrete discontinuity of the ligament with increased fluid intensity signal traversing the defect on T2W images. Other MR signs of ligament injury include being unable to identity the ligament on at least two contiguous images, significant distortion of ligamentous morphology, or an elongated ligament with widening of the intercarpal joint (Fig 24).86 Scapholunate Instability Instability of the scapholunate joint (rotary subluxation of the scaphoid, scapholunate dissociation) is the most-common type of carpal instability.19 The exact degree of injury to the SLL needed to result in instability is controversial. Some believe that a tear involving the dorsal segment of the ligament is enough to result in instability,l* whereas others contend that the entire ligament must be torn or that the palmar radiocarpal ligaments must be injured in addition to the SLL before instability occurs.87 A perforation of the central segment of the SLL doesn’t result in instability.t2 Scapholunate instability occurs when stretching or tear of the SLL dissociates the lunate from the scaphoid and frees the lunate to displace in a volar direction and tilt dorsally. The scaphoid tilts in a palmar direction (rotatory subluxation), and the scapholunate angle increases to greater than 60 degrees. These changes result in the dorsal intercalated segmental instability (DISI) pattern that can be detected on a lateral radiograph or sagittal MR images (Fig 25). Unstable scaphoid fractures can result in a similar appearance because the distal fracture fragment tilts in a palmar direction after it “dissociates” from the proximal fragment and lunate which tilt dorsally, even though the SLL remains intact (Fig 26).19 If left untreated, scapholunate dissociation can lead to the development of the scapholunate advanced collapse pattern (SLAC wrist). In this pattern, the capitate migrates proximally between the scaphoid and lunate with the development of rapidly progressive degenerative changes, most often involving the lunate-capitate and radiocarpal spaces (Fig 27).8” Variable accuracy rates have been reported in the literature for detecting SLL tears with MR imaging. In
Curr Probl
Diagn
Radiol,
November/December
1998
Fig
39. PD/TH.
“Y
images
Bowing
I
demonstrate
ratio.
The
bowing
, 11tunnel. Coronal an ununited scaphoid
ganglion cyst eroding into the trapezoid or tendons in the carpal tunnel.
ratio
is calculated
by dividing
Tl W (A) and axial T2*W (B) fracture (black arrows] and a (white
arrows),
deep
to the flex-
215
FIG 41. Prominent demonstrates a large carpal
vessel vessel
in the carpal tunnel. (v) abutting the flexor
Axial T2’W image tendons deep in the
tunnel.
the two largest series that evaluated SLL tears, sensitivity, specificity, and accuracy ranged from 50% to 90%, 90% to lOO%, and 77% to 90%, respectively, when arthrographic and/or surgical findings were used as the standard of reference.13,s6 As with arthrography, the MR findings must also be viewed with the understanding that not all SLL perforations produce symptoms and that degenerative perforations most often involve the thin, central portion of this ligament. Therefore identification of involvement of the dorsal or volar segments on coronal images may prove to be more predictive of a significant lesion, but this has not been documented in the literature.
FIG
42.
Axial strate
Tl W (A) and fast spin echo
also
the severed the palmar
focal
after
flexor
retinaculum
release.
of the flexor
tendons
which
also
demon-
fluid compatible with tenosynovitis. Focal high sigthe enlarged median nerve (arrowhead) is compati-
nerve
injury.
Instability
Disruption of the LTL is the second-most-common ligamentous cause of carpal instability.19 This allows the triquetrum to tilt dorsally while the lunate, which is still attached to the scaphoid via the SLL, tilts in a volar direction.88 This results in the volar intercalated segmental instability (VISI) pattern in which the scapholunate angle narrows to less than 30 degrees (Fig 28). There is a strong association between tears of the triangular fibrocartilage and LTL tears.19 In general, the diagnosis of LTL tears with MR imaging has proved to be more difficult than for the SLL, probably because of its smaller size. In the two series mentioned previously, the sensitivity, specificity, and accuracy of MRI imaging for detecting LTL tears ranged from 50% to 56%, 45% to lOO%, and 49% to 90% respectively.13J6
216
ends
man,
inversion recovery (6) images demonof the flexor retinaculum (curved arrows). Note
displacement
strate peritendinous nal intensity within ble with
Lonotriquetral
Twenty-six-year-old
Extrinsic
I igaments
The normal MR appearances of the extrinsic carpal ligaments have been extensively described; however, the ability of MRI to diagnose tears of the extrinsic ligaments, and the clinical significance of these injuries, is not well established. As a result, we do not spend much time analyzing the extrinsic ligaments when interpreting MR studies of the wrist. Pathology of the TFC A number of conditions can result in ulnar sided wrist pain including TFC and/or LTL injury, triquetral avulsion fracture, pisotriquetral arthritis, subluxation or tendinitis of the extensor carpi ulnaris tendon, ulnar artery thrombosis, and ulnar neuropathy in Guyon’s
Curr Probl
Diagn
Radiol,
November/December
1998
FIG
44.
Twenty-four-year-old
gery with incomplete image demonstrates level of the hamate. compatible
FIG
43.
Forty-five-year-old
(A)
Axial TlW demonstrate
and absence
ment (curved (arrowheads).
arrow) Note
in a palmar
direction.
woman,
status
after
carpal
tunnel
Diagn
status
after
carpal
tunnel
median
nerve
surT2*W at the nerve
neuropathy.
release.
T2*W (B) images at the level of the pisiform (P) of the flexor retinaculum near its scaphoid attachas well as the residual portion of the retinaculum the enlarged median nerve (M) which is displaced
canal. Additionally, pain resulting from a radial sided disorder may be referred to this region.8g Palmer separated lesions of the TFC into degenerative and traumatic categories, and then created subdivisions based on the location of the lesion-specifically, whether it involved the radial or ulnar margin of the TFC.gO The location of a tear has therapeutic implications because of the vascular supply of the TFC.gl The peripheral 15% to 25% of the cartilage, along its ulnar margin, is well vascularized, and tears in this region may heal with nonoperative therapy. The remaining portions of the TFC (central and radial margins) are essentially avascular. As a result, perforations in these regions are usually debrided, although good results have been reported after operative reattachment of tears and/or avulsions involving the radial margin of the disk.92 MRI is highly accurate in diagnosing TFC injuries.13,86s9,93,g4 Tears or perforations in the central and radial portions of the disk are especially well demon-
Curr Probl
with
woman,
release of the flexor retinaculum. Axial intact flexor retinaculum (curved arrows) Note also the enlargement of the median
Radiol,
November/December
1998
FIG 45. Twenty-nine-year-old with fibrosis around the median absence of the flexor retinaculum
man, status after carpal tunnel release nerve. Axial Tl W image demonstrates at the level of the pisiform (P) with low
signal intensity scarring in the palmar subcutaneous The fibrosis extends deeper (black arrows) around nerve
fat (white an enlarged
arrow). median
(M).
strated (Figs 1.5, 22, 25, 29). Those near the ulnar styloid are less-accurately diagnosed because of the intermediate signal intensity normally present in this portion of the TFC and because post-traumatic synovitis or synovial proliferation in the prestyloid recess can mimic a tear.8g,95 MRI is also able to demonstrate a partial tear or irregularity along the undersurface of the TFC that would be missed at arthroscopy when using standard radiocarpal portals (Fig 30).89 It is important to report the exact location of the tear in the TFC. Tears in its central portion may not account for the patient’s symptoms because the incidence of degenerative, often asymptomatic perfora-
217
Traumatic tears of the TFC are often associated with injuries of adjacent structures. MRI is able to demonstrate these injuries, which include disruption of the ECU tendon sheath and partial or complete tear of the LTL (Fig 31). to1 The depiction of associated injuries of the ulnolunate and ulnotriquetral ligaments is less reliable.94 The disruption of the volar or dorsal radioulnar ligaments is associated with the instability of the DRUJ. MR can demonstrate subluxation and/or dislocation of the DRUJ in the axial plane of imaging,lo2 but it also provides excellent depiction of the radioulnar ligaments, TFC, and other important associated structures (Fig 32). Traumatic disruption of the ECU tendon sheath can result in subluxation of the tendon at the level of the ulnar head and related tenosynovitis. The tendon generally subluxes or dislocates over the styloid process in an ulnar (medial direction) rather than lying in the normal groove on the dorsum of the ulna. The subluxed tendon and signs of associated tenosynovitis are best seen on axial MR images at the level of the distal ulna.to3>lo4 “Dynamic” MRI is performed by imaging the wrist while it is moved from extreme radial to ulnar abduction with a mechanical device. This has been used to detect cases of ulnocarpal impaction not detectable on static images, including cases of impaction related to instability of the ulnar attachments of the TFC.to5 However, this technique is not a part of routine clinical imaging. Tendon FIG 46. Fifty-year-old Tl W [A) and T2*W the hook of the (curved arrow).
man with history of ulnar nerve palsy. Axial (6) images reveal a ganglion cyst (C) adjacent to
hamate,
displacing
the
ulnar
neurovascular
bundle
tions of the central portion of the TFC increases with age. More than 50% of patients over 60 years of age will demonstrate this type of perforation.96 Increased signal intensity can be seen within the TFC on MRI in up to 50% of asymptomatic subjects.97,98 This is probably due in large part to the degenerative changes found in the TFC with advancing age, similar to the men&al degeneration observed in the knee.98 Kang et al found that degenerative changes within the TFC demonstrate intermediate to high signal intensity on TlW images but are of lower signal intensity on T2W images. Conversely, acute tears and perforations demonstrate high signal intensity, similar to fluid, extending through the substance of the TFC on T2W images.99,‘00
218
Pathology
The tendons of the wrist and hand are commonly affected by pathology ranging from tenosynovitis to degeneration to tears. Common etiologies include inflammatory arthritis and chronic repetitive trauma from overuse. Tendons demonstrate low signal intensity on all MR sequences with the exception of the magic angle effect described previously. Tendons may show slightly higher signal intensity near osseous insertions. The tendons of the wrist are best evaluated on axial images. A small amount of fluid in a tendon sheath can be seen in one or more of the dorsal compartments in normal subjects.lo6 Distention of the sheath with fluid completely surrounding the tendon is diagnostic of tenosynovitis, which may be sterile or purulent (Fig 33). Stenosing tenosynovitis is diagnosed when septated and/or loculated fluid is identified within the sheath. With chronic tenosynovitis, the signal intensity of the surrounding material may be more hypointense because of the development of fibrosis. lo4
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Tendon degeneration or partial tears result in enlargement of the affected tendon, and increased signal intensity is often identified within its substance on short echo time (TE) images (Fig 34).lo3 A partial tear represents incomplete disruption of the tendon’s fibers and may appear as a thickened or attenuated tendon or as a discrete focus of increased signal intensity within the tendon on Tl, T2, or GRE images. Absence of a tendon within its sheath on axial images is diagnostic of complete rupture, and MRI can be used to preoperatively assess the degree of separation between the ends of the disrupted tendon. DeQuervain’s
Syndrome
Tenosynovitis of the abductor pollicis longus and extensor pollicis brevis tendons in the first dorsal compartment (DeQuervain’s syndrome) is often idiopathic but is also associated with pregnancy, repetitive lowgrade injury, and direct trauma (Fig 35). It is more common in females and typically manifests with swelling and tenderness over the radial styloid.lo4 Clinical diagnosis is usually straightforward, but occasionally the findings are subtle and the syndrome may be indistinguishable from a scaphoid fracture, flexor carpi radialis tenosynovitis, or degenerative arthritis of the first carpometacarpal joint.to7 Thickening of the tendons and peritendinous edema are the most-reliable MRI findings (Fig 36).lo8
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Probl
Diagn
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November/December
1998
FIG Tl W
47.
(A)
Schwannoma and
of the deep
fast spin echo
a rounded mass (H). Homogeneous
inversion
branch recovery
of the ulnar
nerve.
(B) images
Coronal
demonstrate
(M) along the ulnar aspect of the hook of the hamate high signal intensity on the inversion recovery image
suggests a cyst. However, a fat-saturated, axial Tl W image obtained after the intravenous administration of Gd-DTPA (C) demonstrates relatively homogeneous enhancement compatible with a solid mass. Biopsy revealed
this
to be a schwannoma
of the deep
branch
of the ulnar
nerve.
ECU Tendon The ECU tendon, in the sixth dorsal compartment, is the second-most-common extensor tendon involved with tenosynovitis. This often occurs as a result of repetitive subluxation of the ECU tendon after disruption of its sheath (Fig 37). lo4 Because increased signal
219
FIG
48.
Neural
fibrolipoma
fast spin echo inversion enlargement and tortuosity enlarged, low-signal-intensity trating high-signal-intensity
of the median recovery (B) of the median neuronal
nerve.
Axial
Tl W (A) and
images demonstrate nerve (arrows). In A, fasicles
surrounded
marked note the
by the infil-
fat.
intensity within the ECU tendon may occur in asymptomatic patients, the diagnosis of tendon degeneration or partial tear should be reserved for cases where MRI shows enlargement of the tendon and/or definite peritendinous edema and/or fluid. Ofher Tendons Tendon pathology is also commonly seen in the extensor car-pi radialis, flexor carpi radialis, and flexor car-pi ulnaris tendons. Tenosynovitis of the flexor digitorum tendons is a common cause of carpal tunnel syndrome. lo4 Nerve
Pathology
Compressive
Neuropathies
Carpal Tunnel Syndrome. Carpal tunnel syndrome (CTS) results from compression of the medial nerve within the carpal tunnel. It is the most-common peripheral compressive neuropathy. Affected patients typically present with pain and paresthesias in thumb, index finger, long finger, and radial half of the ring finger. Symptoms are usually worse at night.lo9 The etiology of CTS may be multifactorial. Causes include osseous abnormalties (fracture, callus formation, carpal malalignment), soft tissue changes that narrow the tunnel (mass, hematoma, tenosynovitis, anomalous muscle), and systemic processes (pregnancy, amyloidosis, etc).r lo Space-occupying lesions are more commonly found in patients, with unilateral symptoms.rl’ Some
220
patients suffer from dynamic CTS, which is a cumulative trauma disorder related to repetitive, usually workrelated, microtrauma. Symptoms in these patients typically abate with rest. lo9 The diagnosis is usually made through a combination of clinical findings and nerve conduction studies. MRI is not used as a primary diagnostic modality in this setting, but it has been advocated to detect any underlying causative factors and as a useful adjunct when nerve conduction studies are equivocal.l12 MRI findings in patients with CTS are best seen on axial images and include swelling of the median nerve (best assessed at the level of the pisiform) (Fig 38), flattening of the median nerve, and excessive pahnar bowing of the flexor retinaculuml10 (best assessed at the level of the hamate). The degree of bowing is expressed as a “bowing ratio” (Fig 39). To calculate this ratio, a line is drawn from the triquetrum to the hook of the hamate on an axial image (length = TH). The distance from this line to the flexor retinaculum (palmar displacement = PD) is divided by the length TH.41Ratios in normal subjects range from 0% to 15% (mean =
Curr Probl
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November/December
1998
FIG 49. Dorsal T2*W (C) images scaphoid (S) and appearance, and
ganglion cyst. Sagittal Tl W (A), T2*W (B) and axial reveal a lobulated, septated mass (C) just dorsal to the scapholunate location are
ligament. classic for
Its signal a dorsal
intensity, ganglion
overall cyst. I,
Lunate.
FIG 50. Volar high-signal-intensity the wrist
5.8%) and from 14% to 26% (mean = 18.1%) in patients with CTS. 1lo Increased signal intensity within the median nerve on T2W images has also been described in patients with CTS, but this finding is subjective.“’ MR can also demonstrate any contributory flexor tenosynovitis or space-occupying mass within the carpal tunnel (Figs 40 and 41). In patients with activi-
Curr
Probl Diagn
Radiol,
November/December
1998
just deep
ganglion cyst. Axial T2*W ganglion cyst (C) along to the flexor
carpi
radialis
image demonstrates small the volar, radial aspect of tendon
(curved
arrow).
ty-related symptoms (dynamic CTS), MR imaging before and after exercise has been found to accentuate abnormal MRI findings. 1I3 When conservative treatment fails, release of the flexor retinaculum via an open or endoscopic technique is usually performed in an attempt to increase the volume of the carpal tunnel. Common postoperative MRI findings include an increase in the overall volume of the carpal tunnel with palmar displacement of the flexor tendons, increased fat content in the tunnel or along its palmar aspect, and the development of hypointense scar tissue, typically along the ulnar aspect of the carpal tunnel. 1l4 MRI findings compatible with complete release of the flexor retinaculum include identification of a sur-
221
FIG 52. Giant cell tumor T2W image demonstrates thenar musculature Note the multiple ible with
FIG 5 1. Pisotriquetral arthritis and associated ganglion cyst. Tl W (A) and axial T2*W (B) images demonstrate narrowing pisotriquentral degenerative
Sagittal of the
joint with a small osteophyte (arrow) compatible with arthritis. Note also the associated ganglion cyst or syn-
ovial outpouching aspect of the wrist
arising from the pisotriquetral (C). P, Pisiform; T, triquetrum.
joint,
along
Coronal mass
fast spin echo (arrows) in the
with extension into the distal wrist (curved areas of low signal intensity within the mass,
urrows). compat-
hemosiderin.
Postoperative failures may be attributed to a number of causes, the most common of which is incomplete release of the flexor retinacu1um.l l5 MRI findings suggestive of an anatomic basis for recurrent symptoms include identification of an intact portion of the flexor retinaculum (Fig 44), the development of low signal intensity fibrotic scarring around the median nerve (Fig 45), and proximal swelling of the nerve.l15 MR imaging may also reveal a persistent or recurrent mass lesion within the carpal tunnel or the development of a median nerve neuroma. Ulnar Tunnel Syndrome. The ulnar nerve may become compressed along the course of Guyon’s canal. Etiologies include carpal ganglion cysts or other masses, fracture of the hamate, or repetitive occupational trauma to this region.lo7 The course and status of the nerve as well as any adjacent masses can be assessed on axial images (Fig 46).‘16>r17
the ulnar
gical defect along the entire course of the retinaculum, palmar displacement of the flexor tendons through severed margins of the retinaculum, and absence of the retinaculum (Figs 42 and 43).
222
of the tendon sheath. a large, heterogeneous
Neural
Tumors
Nerve Sheath Tumors. Benign nerve sheath tumors, (schwannoma and neurofibroma) occur in the hand and wrist, with schwannomas having a predilection for involving the ulnar nerve. 1l8 These usually appear
Curr Probl
Diagn
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November/December
1998
FIG 53. Soft tissue hemangioma. Axial TlW (A) and fast spin echo T2W (B) images demonstrate CI lobular mass in the volar soft tissues of the forearm at the level of the distal radioulnar joint. Note the scattered areas
of fat within
the lesion
demonstrating
Tl W image and the homogeneous mass on the T2W image. Punctate, ible with
phleboliths
(open
high
signal
intensity
on the
high signal intensity throughout the low-signal-intensity foci are compat-
arrows).
as a fusiform mass related to a neurovascular bundle that is isointense or slightly hyperintense to muscle on TlW images and of high signal intensity on T2W variable degrees of images. They demonstrate enhancement after contrast administration (Fig 47).11s Although their MR imaging appearance is often non-specific, two MR findings have been described that may help in diagnosing these lesions. The fast, designated the “split fat” sign, describes the peripheral rim of fat often seen surrounding the lesion that is thought to relate to the fat that normally surrounds the neurovascular bundle, the site of origin of these lesions.l18 The “target sign,” described in neurofibro-
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG
(A)
54.
Rheumatoid
arthritis.
Posteroanterior
radiograph
demonstrates diffuse osteoporosis without definite Tl W (B) and T2’W (C) images demonstrate synovial small erosions of the third, fourth, and fifth metacarpals
of the wrist erosion. Axial pannus (P) and (3, 4, 5).
223
FIG
55.
Rheumatoid
arthritis.
PA radiograph
of the wrist
(A) demon
strates small erosions of the capitate (arrowheads). Axial Tl W (6) and inversion recovery (C) images demonstrate apparent tenosynovitis of the extensor digitorum tendons (curved arrows). ed Tl W image obtained after the intravenous
However, a fat-saturatadministration of Gd-
DTPA (D) reveals markedly enhancing pannus around the tendons as well as in the distal radioulnar joint (small arrows]. Note also minimally enhancing brevis image
cent enhancing
mas, refers to central low signal intensity and peripheral high signal intensity on T2W images, which probably correspond to central fibrosis and peripheral myxomatous tissues, respectively.l19 It is impossible to differentiate benign from malignant nerve sheath tumors with MR imaging, but signs suggestive of malignancy include large size (>5 cm), rapid growth, ill-defined borders, and signal heterogeneity.’ l8
224
pannus
between
the extensor
tendon (long arrow). Sagittal (E) demonstrates small erosion pannus
(open
carpi
fat-saturated of the ulnar
radialis
longus
and
Tl W post-contrast head (u) with adia-
arrow).
Neural Fibrolipoma. The benign neural fibrolipoma (also known as fibrolipomatous hamartoma of nerve) is a lesion that most often arises in and causes marked enlargement of the median nerve. Initially, the lesion may be asymptomatic, but patients may go on to develop signs and symptoms of nerve compression.120 In 66% of cases there is associated macrodactyly
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG 56. Rheumatoid arthritis. Axial T2*W image demonstrates pannus in the distal radioulnar joint (asterisk). Additional pannus displaces the extensor carpi ulnaris tendon (Ej. Note also the tenosynovitis involving the first dorsal compartment (arrow).
FIG
55
continued
(macrodystrophia lipomatosa).lls Pathologi-tally this lesion results from infiltration of the nerve by fibrous and fatty tissue. The lesion extends along the expected course of the median nerve and demonstrates a distinctive MRI appearance. It is seen as a serpiginous mass composed of tubular low-signal-intensity structures (probably corresponding to nerve fascicles surrounded by epineural and perineural fibrosis) within a background of high signal intensity fat (Fig 49).120 The differential diagnosis includes an intraneural lipoma, traumatic neuroma, and vascular malformation. 120 Masses The most common mass involving the wrist is the ganglion cyst,121 a fibrous walled structure containing thick, mutinous fluid. These can arise from tendon sheath or synovial tissue from any site. Approximately 60% to 70% are found along the dorsum of the wrist at the level of the scapholunate joint (Fig 49). A small synovial pedicle frequently extends through the dorsal fibers of the scapholunate ligament. Erosion of the ganglion cyst into the radial aspect of the lunate is common (Fig 23). Twenty percent of ganglia arise in the volar soft tissues between the flexor carpi radialis and abductor pollicis longus tendons (Fig 50).122
Cur
Probl
Diagn
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November/December
1998
Although dorsal lesions can be diagnosed with a targeted ultrasound examination,122>123 the ability to demonstrate deeper lesions and other osseous or soft tissue pathology is a distinct advantage of MRI (Fig 5 1).124 A ganglion cyst is a well-circumscribed, low-signalintensity mass on TlW images that demonstrates homogeneous high signal intensity, often with low-signalintensity septations, on T2W images because of its fluid content. It may display a more-heterogeneous signal if complicated by hemorrhage or infection. Gd-DTPA administration is helpful to differentiate a ganglion cyst from other solid masses that demonstrate similar signal characteristics, such as nerve sheath tumors (Fig 47). A ganglion cyst should not demonstrate central enhancement on post-gadolinium images, although enhancement of internal septae may be identified.125 The second-most-common soft tissue mass of the hand and wrist in most series is a giant cell tumor of the tendon sheath.t21 This is a localized, extraarticular form of pigmented villonodular synovitis (PVNS), a hyperplastic synovial process of unknown etiology. The characteristic MR finding of areas of low signal intensity on both TlW and T2W images is related to hemorrhage and resulting hemosiderin deposition within the lesion (Fig 52).126 Benign lipomas are recognized by their characteristic MR signal intensity that parallels fat on all sequences. Most are well circumscribed, but these can appear infiltrative, especially if compressed between tissue planes or if they arise within a muscle.126
225
The MR appearance of a soft tissue hemangioma is also relatively specific. These are usually isointense to muscle on TlW images, often containing some areas of high-signal-intensity fat. On T2W images, they appear as a lobulated mass, often displaying circular or serpentine areas of extremely high signal intensity corresponding to vascular channels and spaces (Fig 53).125 Associated phleboliths appear as punctate low-intensity foci. 126 These typically demonstrate prominent enhancement after the administration of intravenous Gd-DTPA.lr8 Synovial Rheumatoid
Pathology Arthrifis
Rheumatoid arthritis commonly affects the wrist. Detection of early disease is important to optimize therapy and limit the progression of joint destruction. It can be difficult to clinically differentiate proliferative synovitis (pannus) from a joint effusion in these patients,127J28 and radiographs are often normal in the early stages. MRI is able to directly demonstrate inflammed synovium. Pannus typically demonstrates low to intermediate signal intensity on TlW images and increased signal intensity on T2W images (Fig 54).127,12g>130Because these signal characteristics are similar to fluid, the intravenous administration of Gd-DTPA has proved useful for distinguishing between pannus and joint fluid.127-131 Gd-enhanced, fat-saturated TlW images provide superb contrast between the intensely enhancing synovial tissue and the low-intensity joint fluid and suppressed fat.132 Using this technique, MRI is able to demonstrate pannus and bony erosions earlier than is possible with conventional radiographs (Fig 55).133,134 In these early stages, areas of localized enhancement are more commonly seen, while diffuse synovial enhancement is characteristic of more advanced disease.135 Rheumatoid arthritis involves the extensor tendons of the wrist in 50% to 60% of patients, and clinical assessment of the degree of tendon involvement is often inaccurate. lo6 Involvement with pannus is usually manifest on MRI by tendon enlargement and inhomogeneous signal intensity (Fig 56). Fluid in the surrounding sheath is best seen on T2W images, whereas pannus within the sheath or tendon substance is best delineated on post-gadolinium images (Fig 55).lo6 Absence of the tendon within the sheath is consistent with a complete tear, but extensive infiltration of pannus within an intact tendon can mimic a rupture.lo6 MR can also be used to follow the progression or
226
regression of the disease. In a small group of patients who underwent serial MRI scans, those in remission demonstrated decreasing synovial proliferation and bone marrow edema, as well as no new erosions.136 Despite these features, MR is not currently used to diagnose or follow patients with rheumatoid arthritis in most centers. In our practice the two most-common indications for scanning these patients are (1) chronic wrist pain in a patient with negative radiographs, and no history of rheumatoid arthritis who is found to have the typical findings of pannus and erosions on MRI; and (2) a palpable mass in which MR is used to differentiate pannus from tenosynovitis. Summary MR imaging of the wrist has the unique capability of simultaneously demonstrating bone and soft tissue structures. Its exquisite sensitivity for detecting bone marrow edema makes it an ideal screening tool for diagnosing radiographically occult osseous injuries and areas of AVN. This, together with its ability to provide a comprehensive, non-invasive assessment of the ligaments, tendons, nerves, and components of the TFC make MRI a very powerful tool for evaluating patients with wrist pain of uncertain etiology. Its exact role in the work-up of these patients has not been entirely established, but with further advances in technology and the radiologist’s understanding of wrist anatomy and pathology, MRI is assuming a more central role in this clinical setting. REFERENCES 1. Larsen CF, Brondum V, Wienholtz G, Abrahamsen J, Beyer J. An algorithm for acute wrist trauma. J Hand Surg 1993;18B:207-12. 2. Aaron JO. A practical guide to diagnostic imaging of the upper extremity. Hand Clin 1993;9:347-58. 3. Chidgey LK. Chronic wrist pain. Orthop Clin North Am 1992;23:49-59. 4. Young VL, Higgs PE. Evaluation of the patient presenting with a painful wrist. Clin Plast Surg 1996;23:361. 5. Gilula LA, Yin Y. Imaging of the wrist and hand. Philadelphia: WB Saunders. 6. Kneeland JB. Technical considerations for MR imaging of the hand and wrist. Magn Reson Imaging Clin N Am 1995;3:191-6. 7. Stoller DW. The wrist. Semin Roentgen01 1995;30:265-76. 8. Constable RT, Gore JC. The loss of small objects in variable TE imaging: implications for FSE, RARE and EPI. Magn Reson Med 1992;28:9-24. 9. Anderson MW, Raghavan N, Seidenwurm DJ, Greenspan A, Drake C. Evaluation of meniscal tears: fast spin echo versus conventional spin echo magnetic resonance imaging. Acad Radio1 1995;2:209-14. 10. Elster AD. Gradient echo imaging: techniques and
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E. Keats, M.D. Editor-in-Chief
189
Mark
Anderson,
MD,
ing at the University of California, Davis, Medical Center and a fellowship in MRI at the University of California, San Francisco, Medical Center. He is an associate professor of radiology at the University of Virginia Health Sciences Center in Charlottesville, Virginia.
medical degree from the University of Nebraska College of Medicine. She did her residency training at the University of Nebraska Medical Center. Dr. Kaplan is a professor or radiology and orthopedics at the University of Virginia Health Sciences Center in Charlottesville, Virginia, and is also codirector of the Section of Musculoskeletal Imaging. Robert G. Dussault, MD, received his BA degree from the Jean de Brebeuf College, Montreal, Que. . bet, Canada, and his medical Lb degree from the University of Sherbrooke, Sherbrooke, Quebec, Canada. Dr. Dussault is a professor of radiology and orthopedics at the University of Virginia Health Sciences Center in Charlottesville, Virginia, and is codirector of the Section of Musculoskeletal Imaging. Gregory G. Degnan, MD, received his BA degree from Virginia Wesleyan College in Norfolk, Virginia, and his medical degree from Eastern Virginia Medical School in Norfolk, Virginia. He did his residency training at the naval hospital in Portsmouth, Virginia, and a fellowship in hand and microvascular surgery at Thomas Jefferson Medical College in Philadelphia, Pennsylvania. Dr. Degnan is an assistant professor of surgery at the Uniformed Services University of Health Sciences, Bethesda, Maryland, and is an assistant professor of orthopedic surgery at the University of Virginia Health Sciences Center in Charlottesville, Virginia.
190
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1998
Magnetic
Resonance
Imaging
Mark W. Anderson,
MD
Phoebe
A. Kaplan,
MD
Robert G. Dussault,
MD
Gregory
G. Degnan,
Wrist abnormalities are often complex and difficult to diagnose.Clinical assessmentcan be extremely challenging, and as a result, diagnostic imaging usually plays a central role in the evaluation of patients with wrist pain. Conventional radiography, radionuclide bone scan, conventional and computed tomography, and arthrographyhave been most often emphasizedin imaging alogrithms for the work-up of patients with wrist pain, with magnetic resonanceimaging (MRI) relegatedto a secondaryrole.lT5This is likely due to a number of factors. The anatomy of the wrist is complex, and the structures of interest are small. Early MR scanslacked the resolutionrequiredto demonstratethe necessarydetail. Even with the technologic advancesavailable today, a lack of sufficient attention to technical details can result in a non-diagnosticscan.Additionally, the radiologist’s understandingof wrist anatomy has had to evolve along with the technology,and many MR findings once consideredpathologic have been shown to representeither normal variants or clinically insignificant findings in asymptomatic individuals. Despite thesechallenges,MRI has clear advantages over other techniques;it is the only imaging examination that simultaneouslydemonstratesboth osseousand soft tissue structures.Maximizing the diagnosticutility of a wrist MR examinationdependson 3 factors:(1) the ability to producehigh-resolutionimages,(2) the developmentof a systematicapproachto image analysis,and (3) a thoroughknowledgeof normal wrist anatomyand the pathologic entities that commonly affect it. The first sectionof this review is a step-by-stepguide describinghow to set up and acquirea high-resolution study.This is followed by a discussionof normal wrist anatomyin the contextof our approachto image analysis. Finally, we will review common types of wrist pathology and offer our thoughtsregardingthe role of MRI in thework-up of a patientwith wrist pain. Our purposeis to providea useful andpracticalguidefor the performanceandinterpretationof MR studiesof the wrist. Curr Probl
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of the Wrist
MD
MRI Technique General
Considerafions
To achieve the spatial resolution necessaryto demonstrate the small structuresof interest, a small field of view (8 to 12 cm), thin slice thickness(1 to 3 mm), and a high imaging matrix (196 to 512) are used.Because each of these factors tends to decreasethe signal-tonoise ratio and overall image quality, a surface coil must be used.6 Numerouscoils areavailablefor wrist imaging. These include dedicatedwrist coils, a flexible (wrap-around) coil, anorbit coil, small circular coils (usuallyin a paired configurationalongthe volar and dorsal surfacesof the wrist), and-in some cases-a standardextremity coil. But not all coils arecapableof generatingthe signal-tonoise ratio and homogeneouspenetrationrequired for optimal imaging, and therefore direct comparison of images from different coils is helpful when selecting equipment.Whichevercoil is used,it shouldbe centered 1 finger-breadthdistal to the ulnar head. Patient Positioning It is of prime importanceto assurethat the patient is in a comfortableposition to minimize motion-relatedartifacts that degradeimage quality. This is most often accomplishedby scanningthe patient in a supineposition with the wrist held at the side. However, if the patient is large,this may not be physically possible.In that case,the patient is placed in a proneposition with the arm held over the head.Paddingplaced at pressure points is essentialfor comfort in this position. Because of the wide rangeof motion at the wrist, careshouldbe takento place the wrist in a neutralposition by aligning the long axesof the radiusand metacarpalswhile minimizing ulnar/radial and dorsal/volarangulation.7Once the patient is in a comfortableposition and satisfactory wrist positioning has been attained,passiverestraints such as sandbags,tape,or foam rubber shouldbe used for maximal immobilization of the wrist. 191
FIG 1. Occult triquetral fracture. Coronal fast spin echo inversion recovery (A) and coronal T2*W (6) images demonstrate high-signal-intensity edema within the triquetrum (arrow) compatible with bone contusion. Note the poor demonstration of marrow edema on the gradient echo image. Note also the low-signal intensity-cartilage contrasted with joint fluid on the inversion recovery image and the similar signal intensities of articular cartilage
TABLE
and
joint
fluid
1. Standard
Imaging
Plane
Coronal Coronal Coronal Axial Axial Sagittal
on the gradient
imaging
Pulse
image
(small
arrows).
protocol
Sequence Tl GRE-T2* FSE-IR Tl GRE-T2* Tl
echo
TR (MSec)
TE (MSec)
450 480 3915 450 600 550
12 18 29 12 18 12
TR, Repetition
time; TE, echo time; TI, inversion
Imaging
Protocol
time; NEX, number
Flip angle 90 30 180 90 30 90 of excitations;
Our basic wrist MRI protocol includes Tl-weighted (TlW), gradient echo T2*-weighted (GRE-T2*W), and fast spin echo inversion recovery (FSE-IR) sequences in the coronal plane. Axial TlW and GRE-T2*W images are also acquired, followed by a sagittal TlW sequence. In cases of suspected mass, infection, or inflammatory arthritis, fat-saturated TlW images are obtained in the coronal and axial planes after the administration of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). Other parameters are shown in Table 1. Pulse Sequences Spin Echo. TlW images are useful for delineating anatomic planes, marrow architecture, fat content in masses, and subacute hemorrhage. The value of T2W imaging is related in large part to the increased signal
192
(degrees)
TI (MSec)
Slice Thickness
150 -
(mm)
3 2 3 3 3 3
Matrix 384x 384x 434x512 384x 384x 384x
NEX
FOV (cm)
1 1 1 1 1 1
10
512 512 512 512 512
10 10 10 10 10
FOV, field of view.
intensity of fluid on these scans, which often highlights pathologic processes. However, we do not include a conventional T2W sequence in our standard protocol because of the suboptimal image quality caused by long acquisition times that result in patient discomfort and motion artifacts. Fast Spin Echo. The fast spin echo (FSE) (also known as turbo spin echo) technique allows for much more rapid acquisition of T2W images because multiple echoes are obtained from each 90-degree pulse, as opposed to a single echo in conventional T2W imaging. This provides several options. Compared with a conventional T2W sequence, the same number of images of equal resolution can be acquired with an FSE sequence in a fraction of the time. Alternatively, images of higher resolution or with an improved signal-tonoise ratio can be obtained by increasing the imaging matrix or number of signal averages, respectively, without increasing the overall imaging time.6
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Despite these advantages, we do not use FSE imaging in the wrist because it also has certain drawbacks. Blurring along tissue margins is common on FSE images, especially with proton density or Tl W sequences. This is most pronounced in tissues with short T2 values,s such as the mensici in the knee, and has resulted in decreased sensitivity in detecting meniscal tears.9 Given the similar histologic structure and MR appearance of the triangular fibrocartilage and intrinsic ligaments, tears of these structures could theoretically be missed as well. The FSE technique is also very gradient intensive, as are the small fields of view and thin slices used in wrist imaging. This refers to the amount of power required by the magnetic gradients, and since this is limited, some type of trade-off is often required with FSE imaging, such as increasing the field of view or slice thickness.6 A final drawback of FSE imaging is the high signal intensity of fat on FSE T2W images. As a result, soft tissue and especially marrow pathology may be obscured because of the similar signal intensity of fat and fluid on these images. This can be overcome by applying a frequency-selective fat-saturation pulse, thereby making any bright signal from fluid or edema very conspicuous against the dark background of suppressed fat. Any heterogeneity in the magnetic field, however, can result in patchy fat saturation that may mimic pathology when none is present. Inversion Recovery. Traditionally, conventional inversion recovery (STIR) sequences suffered from long acquisition times, a limited number of slices, and a poor signal-to-noise ratio. However, these drawbacks have been almost completely overcome with the development of an FSE-IR technique. FSE-IR images are extremely sensitive for detecting soft tissue and marrow pathology (Fig 1). We use this sequence in the coronal plane to assess for bone contusions and occult fractures as well as any fluid collections. Fluid may also be evident within ligament tears or perforations, but the spatial resolution obtained with this sequence is worse than with GRE. Gradient Echo. There are a number of different GRE sequences, but all rely on the use of a gradient reversal to produce the echo rather than the 180-degree pulse used with spin echo sequences. lo (Because of this difference, T2W images obtained with a GRE sequence are designated T2* .) GRE imaging can be performed by using a 2dimensional multislice or a 3-dimensional “volume” technique. The latter provides extremely thin sections
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FIG 2. Axial Tl W image at the level of the scaphoid (SC) and pisiform (P) showing proper orientation of coronal (C) and sagiftal (S) scanning planes.
FIG 3. Coronal Tl W image demonstrating the distal radial ulnar joint (small arrows), radiocarpal joint (R), and midcarpal joint (M). Note also the low-signal-intensity trabeculae coursing through the high-signalintensity marrow fat. TABLE Coronal
Axial
Sagittal
2. Anatomy
of interest
based
on imaging
plane
Osseous architecture Scapholunate ligament Lunotriquetral ligament Triangular fibrocartilage Volar and dorsal radioulnar ligaments Extrinsic ligaments Tendons Median nerve/carpal tunnel Ulnar nerve/Guyon’s canal Distal radioulnar joint Pisotriquetral joint Carpal alignment Pisotriquetral joint Extrinsic ligaments (in cross section)
193
FIG
4.
Normal
coronal
anatomy.
Sequential
radiotriquetral ligament; DRU, dorsal radioulnar cus homolog; P, pisiform; PS, prestyloid recess; ment; S, scaphoid; SLL, scapholunate ligament;
coronal
images
from
volar
(A)
to dorsal
(G).
C, Capitate;
DRUJ,
distal
radioulnar
joint;
DRT, dorsal
ligament; F, flexor tendons: L, lunate; LTL, lunotriquetral ligament; MN, median nerve; MH, menisRCL, radial collateral ligament; RLT, radiolunotriquetral ligament; RSC, radioscaphocapitate ligaTM, trapezium; TD, trapezoid; TFC, triangular fibrocartilage; T, triquetrum; VRU, volar radioulnar
ligament.
(less than 1 mm) and nearly isotropic resolution (equal pixel dimensions in all directions) so that reformatted images can be generated in virtually any plane without a loss of resolution.’ l Because this often requires relatively lengthy imaging times, we prefer the 2-dimensional technique, inasmuch as it is also capable of providing thin
194
slices and exquisite depiction of small structures. Ligaments and articular cartilage are especially well demonstrated with these sequences. We obtain T2*W images in the coronal plane to evaluate the intrinsic and extrinsic ligaments, triangular fibrocartilage, and articular cartilage. Axial T2*W images are useful for evaluat-
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1998
(FIG 4,
continued)
ing tendons, the distal radioulnar joint, the carpal tunnel, and Guyon’s canal. Potential drawbacks of GRE imaging include relatively poor contrast resolution in other soft tissues, increased signal within ligaments and tendons because of the magic angle effect (discussed below), and poor depiction of marrow edema (with high field-strength units) because of susceptibility effects at the interface between cancellous bone and marrow fat (Fig 1). Gd-DTPA. We administer intravenous Gd-DTPA in cases of suspected mass (to separate cystic from solid
Curr Probl
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lesions), infection (to identify soft tissue abscesses), or inflammatory arthritis (to better differentiate synovium and pannus from joint fluid). We do not use Gd-DTPA for other routine clinical indications. Enhancement is most conspicuous on TlW images combined with frequency-selective fat-saturation. The use of inn-a-articular gadolinium in the wrist has been described, but it increases both the time and expense of the examination. Although the depiction of intra-articular structures and ligamentous pathology is superb with this technique,12 the added value to conventional MRI of the wrist has been found to be marginal, and its routine use would not justify the added cost and time.13 Imaging Planes. Our standard imaging protocol includes all three conventional planes: coronal, axial, and sagittal. It is important to prescribe the coronal and sagittal images from an axial slice at the level of the pisiform to assure that these images are acquired in true orthogonal planes. Coronal images are obtained parallel to a line joining the volar surfaces of the pisiform and scaphoid bones, and sagittal images are aligned perpendicular to that axis (Fig 2). Coronal images are best for evaluating osseous architecture, the triangular fibrocartilage complex, and the intrinsic and extrinsic ligaments of the wrist. The tendons of the wrist, the carpal tunnel, Guyon’s canal, and the distal radioulnar joint are best visualized in the axial plane. Some centers do not obtain sagittal images, but we find that they are useful for analyzing carpal alignment, the pisotriquetral joint, and the extrinsic ligaments in cross section and for further evaluating abnormalities seen in other planes (Table 2).
195
FIG 5. Normal axial anatomy. Axial T2*W images at ihe level of the distal radioulnar level of the hamate (C, D). C, Capitate; DRUJ, distal radioulnar joint; extensor tendons: extensor carpi radialis longus; . . . digit1 mmlmi; 9, extensor carpi H, hamate; LT, Lister’s tubercle; UNV,
ulnar
Normal
neurovascular
Anatomy
4, extensor
carpi
radialis
brevis;
5, extensor
longus;
6, extensor
digitorum;
7, extensor
indicis;
8, extensor
ulnaris (ECU); FR, flexor retinaculum; F, flexor digitorum tendons: FCR, flexor carpi radialis; KU, flexor carpi MN, median nerve; P, pisiform; RA, radial artery; S, scaphoid; TM, trapezium; TD, trapezoid; T, triquetrum;
ulnaris; U, ulna;
bundle.
(see Figs 3 through
6)
Osseous The head of the distal ulna articulates with the sigmoid notch of the radius, forming the distal radioulnar joint (Fig 3), a pivot joint that allows for a wide range of pronation and supination. A thin layer of articular cartilage is usually seen along the surface of the ulnar head. The distal articular surface of the radius is normally positioned at the same level as the convex surface of the ulnar head on coronal images. Ulna plus or ulna minus variance refers to a more distal or proximal position of the ulna relative to the radius.14 Under norma1 conditions, the radius can shorten 1 to 3 mm with respect to the ulna depending on arm position.15 Lister’s tubercle is a small osseous prominence along the dorsal margin of the distal radius.
196
pollicis
joint (A), pisiform (6) and T2*W and Tl W images at the 1, abductor pollicis longus; 2, extensor pollicis brevis; 3,
The radiocarpal compartment lies between the distal radius and the triangular fibrocartilage proximally and the proximal carpal row distally, which is made up of the scaphoid, lunate, triquetrum, and pisiform (from lateral to medial). The lunate is tightly bound to the scaphoid and triquetrum by interosseous ligaments along their proximal aspects. Both the scaphoid and lunate have tenuous blood supplies, placing them at higher risk for avascular necrosis.16 The triquetrum articulates with the pisiform, a sesamoid of the flexor carpi ulnaris tendon. In at least 40% of wrists, a communication exists between the radiocarpal and pisotriquetral joints.5>17 The pre-styloid recess is a small synovial extension of the radiocarpal compartment along the volar tip of the ulnar styloid. Articular cartilage along the distal radius can be seen to wrap around its ulnar margin at the attachment of the triangular fibrocartilage.
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1998
FIG 6. Normal sagittal anatomy. Sagittal TlW images at the level of the scaphoid (A), lunate (B), and triquetrum (C). C, Capitate; DRT, dorsal radiotriquetral ligament; L, lunate; RLT, radiolunotriquetral ligament; RSC, radioscaphocapitate ligament; S, scaphoid; TFC, triangular fibrocartilage; T, triquetrum; U, ulna.
The mid-carpal compartment extends between the proximal carpal row and distal carpal row, which is composed of the trapezium, trapezoid, capitate, and hamate. This compartment also communicates with the carpal metacarpal joint spaces, usually via the space between the trapezium and trapezoid.5 The capitate is the largest carpal bone, and with the lunate it forms a strong central column that is integral for flexion and extension. Because of marrow fat, the bones normally demonstrate homogeneous high signal intensity on TlW images (with the exception of low signal intensity trabeculae and bone islands [Fig 31) and low signal intensity on FSE-IR images. On GRE-T2”W images, marrow signal intensity depends on the concentration of trabeculae. In areas of abundant trabeculae, which include the carpal bones and distal radius and ulna, marrow signal intensity is quite low because of susceptibility effects at the bone-fat interfaces. Cortical margins are of low signal intensity on all pulse sequences.
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197
FIG 9. Axial Tl W image shows the median nerve (arrows) between the flexor digitorum tendons at a deeper level than
interposed is normally
seen.
FIG 7. Coronal T2*W image shows both limbs of the triangular cartilage (T) attaching to the ulnar styloid with high-signal-intensity sue between them. Note also the normal scapholunate (small and
lunotriquetral
(arrowhead)
intensity cartilage and displaying their substance, a normal variant.
FIG 8. between (arrow].
Coronal T2*W the triangular
ligaments intermediate
image demonstrates fibrocartilage (7’)
attaching signal
to
high-signal-
intensity
the pre-styloid and meniscus
fibrotisarrow) within
recess (P) homolog
Carti/age/Synovium Thin layers of articular cartilage are normally visible on coronal images along the ulnar head and distal radius
198
FIG lunate
10.
Carpal
related
the capitate
alignment. to positioning
(C) and
lunate
Sagittal
Tl W image
of the wrist (I) remain
in slight colinear.
reveals dorsi
dorsal flexion.
F, Flexor
tilt of the Note
that
tendons.
(including along its ulnar margin at the attachment of the triangular fibrocartilage) and around most surfaces of the carpal bones. Normal cartilage is bright on GRE-T2*W
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1998
FIG 11. Magic angle effect. Axial TlW (A) demonstrate homogeneous intermediate signal
and T2’W (B) images intensity within the ten-
dons on the Tl W image, which partially resolves on the gradient echo image. The involvement of multiple tendons and lack of tendon enlargement
or surrounding
fluid
also argue
against
true
pathology.
images. It is easily distinguished from dark subchondral bone, but it can be difficult to separate from joint fluid on these images (Fig 1). Cartilage is of moderately low signal intensity on FSE-IR and fat-saturated FSE-T2W images, resulting in striking contrast with the high signal intensity of joint fluid (Fig 1). Even so, subtle cartilage defects are difficult to identify on MR images because the articular cartilage is so thin in the wrist. Normal synoviurn is not visible on MR images. ligamenfs Wrist stability is maintained primarily through ligamentous support. The ligaments of the wrist are divided into intrinsic and extrinsic groups. Intrinsic Ligaments. The intrinsic carpal ligaments extend between the carpal bones and are important for maintaining wrist stability by limiting osseous motion. The scapholunate ligament (SLL) and lunotriquetral ligament (LTL) are clinically the most important and can be routinely demonstrated on high-resolution coronal MR images. The SLL is a C-shaped, band-like structure that joins the medial aspect of the proximal pole of the scaphoid to the lateral aspect of the lunate.18 Three distinct por-
Curr Probl
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1998
FIG 12. Accessory extensor digitorum
muscle. Axial Tl (A) and T2 (B) images brevis manus muscle [arrows) surrounding
sor tendon of the index finger (open neous signal intensity, which parallels
arrow). Note its relative that of skeletal muscle.
reveal an the extenhomoge-
tions have been described: dorsal, middle, and v01ar.~~ The dorsal and volar segments are the strongest and most important for maintaining stability at the scapholunate articulation.20 The middle portion is relatively thin, and asymptomatic perforations of this segment are common. 21 On high-resolution GRE coronal images, the volar portion of the SLL is trapezoidal in shape, and its signal intensity is typically higher than that of the middle and dorsal segments, presumably because of the looser connective tissue in this portion. The middle segment displays a triangular shape. The band-like dorsal segment is of low signal intensity owing to densely arranged collagen fibers. 22 Each portion of the ligament may attach to bone or cartilage, and the specific pattern of attachment varies from patient to patient.22 The LTL links the proximal, ulnar aspect of the lunate with the adjacent proximal radial aspect of the triquetrum. It is smaller than the SLL, measuring only 2 mm in thickness, and consequently was less consistently demonstrated with early MR techniques.23 However, it is routinely depicted on high-resolution GRE coronal
199
FIG 13. images zoid
Occult bone contusion. Axial Tl reveal abnormal, edema-like signal
(arrows)
compatible
with
a bone
(A)
and coronal intensity within
T2”W (B) the trape-
contusion.
images. In most cases it is a linear or delta-shaped band of homogenous low signal intensity.23 Intermediate signal intensity may extend partly or completely across the SLL or LTL in asymptomatic patients. 23,24Ligament tears or perforations can display a similar appearance on Tl proton density and some GRE sequences but should demonstrate high signal intensity that is equal to that of fluid on T2W or T2*W images. Extrinsic Ligaments. The extrinsic carpal ligaments course obliquely across the volar and dorsal surfaces of the wrist and attach the cat-pus to the forearm. The MR appearances of the extrinsic ligaments have been extensively described in the literature. 12,25-30These intracapsular, extra-synovial structures assist in maintaining wrist stability and appear as striated, band-like struc-
200
tures of alternating low and intermediate signal intensity on coronal GRE images. They are displayed in cross section on sagittal images.29 The primary volar ligaments include the radioscaphocapitate, radiolunotriquetral (also known as the long radiolunate), and short radiolunate ligaments.31 These are stronger and more important stabilizers than the extrinsic ligaments on the dorsum of the wrist. The radioscaphocapitate ligament extends from the radial styloid, across the waist of the scaphoid to attach to the capitate. The fibers that course from the most-distal aspect of the radial styloid to the tubercle of the scaphoid have been described as the radial collateral ligament.31 The radiolunotriquetral ligament is the largest and strongest ligament of the wrist.32 It also originates from the radial styloid process, just ulnar to the radioscaphocapitate ligament, and then follows a more horizontal course with attachments to the lunate and triquetrum. The short radiolunate ligament arises from the volar surface of the radius at the level of the lunate and extends to its volar surface.31 The major dorsal extrinsic ligament, the radiotriquen-al ligament (or dorsal radiocarpal ligament), is a thickening of the dorsal wrist capsule. It originates from the ulnar aspect of Lister’s tubercle and attaches to the dorsal surfaces of the scaphoid, lunate, and triquetrum.31~33 These structures are often difficult to identify, even with thin-section imaging. Because of their oblique orientation, they are virtually never seen in their entirety on one image. Three-dimensional GRE imaging has been advocated for depicting these structures via reformatted images in specialized planes.27>28We do not use this technique because of the extra time involved and because the status of the individual extrinsic ligaments is not of clinical importance to our orthopedic hand surgeon. Triangular Fibrocarthge Complex The triangular fibrocartilage complex is composed of several soft tissue structures along the ulnar aspect of the wrist: the triangular fibrocartilage, the volar and dorsal radioulnar ligaments, the meniscus homolog, the ulnocarpal ligaments, the ulnar collateral ligament, and the sheath of the extensor carpi ulnar-is (ECU) tendon.34,35 It is best seen on coronal images and has 3 major functions: (1) cushioning axial forces across the ulnar carpal region, (2) stabilizing the ulnar carpus, and (3) stabilizing the distal radioulnar joint (DRUJ).34 The triangular tibrocartilage (TFC) extends from a broad attachment along the ulnar margin of the distal radius to the ulnar styloid. The thickness of the TFC has
Curr
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November/December
1998
FIG 14. Occult distal in more-diffuse edema
radial fracture. Coronal in the distal radius.
FIG 15. Occult scaphoid distal pole of the scaphoid
(A)
Tl
fracture. Coronal Tl W with associated edema.
and inversion
(A) Note
recovery
Probl
Diagn
Radiol,
November/December
1998
demonstrate
a curvilinear
a non-displaced and coronal T2’W (8) images demonstrate also the small perforation within the triangular fibrocartilage
been found to be inversely proportional to the degree of ulnar variance.36 That is, the TFC tends to be thinner in patients with positive ulnar variance and thicker in those with negative ulnar variance. On coronal images the TFC appears as a bow-tie-shaped structure of relatively
Curr
(B) images
fracture
line (small
curvilinear (small
fracture
arrows)
with-
line at the
arrow).
low intensity with or without patchy areas of intermediate signal intensity. 35 The high signal intensity hyaline cartilage at its radial attachment should not be confused with a tear. The TFC often attaches to the ulnar styloid via two striated bands, one inserting at the base of the
201
FIG
16.
the hook
FIG
17.
Twenty-three-year-old
baseball
of the hamate
The corresponding
(arrow).
Twenty-nine-year-old
nal T2*W (B) images demonstrate pole of the scaphoid as evidenced patible
with
man with
player
with occult
triquetral
axial
hamate T2”W
fracture
fracture.
image
and
Tl W image
scaphoid
fracture
(A)
d emonstrates
the high-signal-intensity
complicated
abnormally fracture
by avascular
necrosis.
low signal
intensity
line at this site (curved
Coronal
Tl W
(A)
within arrow).
and
coro-
a small avulsion fracture involving the proximal triquetrium (curved arrows) as well as a fracture of the proximal by a slight cortical step-off (short arrow). The low signal intensity within the proximal pole on both imuges is com-
AVN.
styloid and the other near its tip (Fig 7). Loose areolar tissue between these bands produces intermediate signal intensity that also mimics pathology.35 As with the intrinsic ligaments, a true tear or perforation should be diagnosed only when the traversing signal is equal to that of fluid on T2W or T2*W images. The volar and dorsal radioulnar ligaments are bandlike condensations along the margins of the TFC that function to stabilize the DRUJ.37 These striated bands are consistently seen on coronal images along the most palmar and dorsal aspects of the TFC35 and can be differentiated from it by recognizing that they attach directly to the radius rather than to the articular cartilage. The dorsal ligament blends with the dorsal wrist capsule and sheath of the extensor carpi ulnaris tendon. The volar ligament blends with the volar ulnocarpal (ulnolunate and ulnotriquetral) ligaments that help stabilize the ulnar aspect of the wrist.38 These two ligaments are even less consistent-
202
Axial
(B) demonstrates
ly demonstrated on MR images than are other extrinsic ligaments, and they often appear as a single, intermediate signal intensity sheet of tissue extending from the volar radioulnar ligament to the volar surfaces of the lunate and triquetrum.35 The meniscus homolog is a longitudinally oriented thickening of the capsule extending from the ulnar styloid to the triquetrum. The prestyloid recess is located between the meniscus homolog and TFC and demonstrates a variable amount of volar extension (Fig 8).34 The meniscus homolog is not present in all patients and therefore may not always be seen, even on high-resolution images.35 The extensor carpi ulnaris tendon provides support along the ulnar aspect of the wrist and is best evaluated on axial images. The ulnar collateral ligament, which extends from the ulnar styloid to the triquetrum, is more of a thickening of the capsule than a discrete structure, and it has little mechanical strength.z5>39
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Tendons The tendons of the wrist are best depicted in the axial plane. The extensor tendons are stabilized along the dorsum of the wrist by the extensor retinaculum, a band-like thickening of the antibrachial fascia that courses from the distal forearm to the bases of the metacarpals. 4o Septa extending from the superficial to the deep layers of the fascia form 6 dorsal compartments that contain the extensor tendons. The first dorsal compartment, along the radial border of the distal radius, contains the abductor pollicis longus and extensor pollicis brevis tendons. The second dorsal compartment holds the extensor carpi radialis longus and brevis tendons and is separated from the extensor pollicis longus tendon in the third dorsal compartment by Lister’s tubercle. The extensor digitorum and extensor indicis tendons lie in the fourth compartment. The fifth dorsal compartment contains the extensor digiti minimi tendon, and the extensor carpi ulnaris tendon is found in the sixth compartment. Nine flexor tendons of the wrist lie within 3 common synovial sheaths that travel through the carpal tunnel.16 The flexor digitorum profundus tendons lie deep to those of the flexor digitorum superficialis. The flexor car-pi radialis tendon courses along the radial aspect of the tunnel and can be consistently identified in a shallow groove along the ulnar margin of the trapezium. The flexor car-pi ulnaris tendon lies along the superficial, volar aspect of the wrist and inserts on the pisiform, with some fibers continuing distally to insert on the hamate and fifth metacarpal. The ulnar vessels and nerve are seen just deep to this tendon.
Carpal Tunnel The carpal tunnel is the fibro-osseous space found along the concave volar aspects of the carpal bones.16 It contains the flexor tendons described above and the median nerve. The palmar aspect of the tunnel is bounded by the flexor retinaculum, a dense fibrous band that extends from the scaphoid to the pisiform proximally and from the tubercle of the trapezium to the hook of the hamate distally. The retinaculum normally demonstrates slight palmar bowing.41 There is normally very little fat within the carpal tunnel, but when it is present, it lies dorsal to the flexor tendons. Nerves The median nerve typically lies within the volar, radial aspect of the carpal tunnel just deep to the retinaculum, although its position and shape vary with wrist position
Curr Probl
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1998
FIG 18. saturated, mid-scaphoid abnormality row
edema
Ununited scaphoid fracture. Coronal Tl W (A) and coronal fast spin echo T2W (B) images reveal a fracture through with edema along the distal fracture throughout the proximal pole is consistent versus
ischemic
fatthe
margin. Signal with bone mar-
change.
(Fig 9):2 The nerve demonstrates slightly higher signal intensity than muscle or tendon on TlW images because of its fat content and, as a result, it is usually easy to identify among the low signal intensity tendons. A stippled appearance on axial images reflects the longitudinally oriented fascicles of high signal intensity neuronal fibers that are enclosed in the lower signal
203
intensity perineurium and epineurium.43 The median nerve is oval proximal to and within the carpal tunnel but slightly flattens at the level of pisiform. It normally maintains its size or becomes progressively smaller as it courses through the carpal tunneL41 The ulnar nerve and artery course through Guyon’s canal along the lateral aspect of the pisiform. The floor of the canal is formed by the flexor retinaculum and hypothenar musculature and its roof is formed by a fascial layer that is a distal extension of the antibrachial fascia.44 The ulnar artery lies lateral to the nerve and just superficial to the flexor retinaculum.45 Imaging
Pitfalls
Carpal
Alignment
The alignment of the carpal bones on sag&al images depends on wrist position (Fig 10). The lunate tends to volarflex and dorsiflex relative to the radius when the wrist is placed in radial and ulnar deviation, respectively.46 This highlights the need for careful positioning of the wrist in a neutral position. If needed, the carpal angles can be measured on sequential sagittal scans, analogous to a lateral view of the wrist. Tendons FIG coronal images oatible
19.
AVN
of the
lunate
(Kienbijck’s
disease).
Sagittal
204
(A),
TlW (B), and coronal fat-saturated, fast spin echo TZW (C) demonstrate diffusely abnormal signal within the lunate comwith AVN. Small foci of increased sianal intensitv on T2W imaae I
suggest
Tl W
areas
of revascularization.
Normal variations in the appearance of the wrist tendons may simulate pathology. Spuriously increased signal intensity may occur within tendons because of the magic angle effect. This is related to the orientation of the collagen bundles within the tendon and occurs on
Curr
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November/December
1998
images obtained with a short TE (Tl, proton density, and most GRE sequences) when the tendon lies at an angle near 55 degrees to the main magnetic field.47 This increased signal disappears on long TE (T2W) images, which allows for differentiation from true tendon pathology (Fig 11). The magic angle effect may occur in any tendon, depending on the patient’s arm position, and is commonly seen in the extensor pollicis longus because of its oblique course. Increased signal is also commonly present in the extensor carpi ulnaris tendon, although its exact etiology is unknown.48 Another potential pitfall is related to the multiple tendinous slips of the abductor pollicis longus that may be mistaken for longitudinal tears. 48 In each case, these normal variants should be distinguished from true tendon pathology by the lack of tendon enlargement, surrounding fluid and/or peritendinous edema. Anomalous
Muscles
Anomalous muscles are relatively common in the hand and wrist, particularly the accessory palmaris longus muscle. 4g This muscle is identified along the volar soft tissues of the wrist, superficial to the flexor digitorum tendons and medial to the flexor carpi radialis tendon.50 Another anomalous muscle, the extensor digitorium manus brevis muscle, is found on the dorsum of the wrist along the ulnar side of the extensor indicis tendon (Fig 12).51 An anomalous muscle can present as a soft tissue mass, or it may compress the median or ulnar nerve, depending on its location.52 These demonstrate a
Curr
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Diagn
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November/December
1998
FIG 20. Focal AVN. Coronal TlW (A) and fast spin echo inversion recovery (B) images demonstrate abnormal signal within the lunate that is shown to involve the dorsal half of the bone on the sagittal Tl W image (C)(arrow). The increased signal intensity patible with an earlier stage of the disease digitorum tendons.
on the FSE-IR image or revascularization.
is comF, Flexor
205
FIG 21. Capitate fracture with associated AVN. Coronal Tl W (A) and T2*W (B) rma g es d emonstrate mal capitate compatible with AVN and collapse of the proximal articular surface. Fluid is seen extending tion of the capitate
FIG 22. Ulnolunate gular fibrocartilage
on the T2*W
image
impaction syndrome. (curved arrow), and
signal
intensity
wrtnm
bone
tne proxr-
and central
por-
(arrowheads).
Coronal subchondral
positive ulnar Tl W (A) and T2*W (B) tma g es d emonstrate cystic changes in the adjacent lunate (small arrows).
homogeneous MR appearance and follow muscle intensity on all sequences, features that help to differentiate an anomalous muscle from other soft tissue masses.50
TFC and Ligaments The high signal intensity of the hyaline cartilage along the radial attachment of the TFC should not be misinterpreted as a tear or detachment (Fig 4, C and D).
206
abnormal
into the subchondral
variance,
a perforation
of the trian-
Similarly, the intermediate signal intensity of the loose areolar tissue between its two ulnar limbs should be distinguished from a tear, which will display fluid signal intensity on T2W images (Fig 7).48 Heterogeneous, intermediate signal intensity secondary to myxoid degeneration may be seen within the TFC as well as the scapholunate and lunotriquetral ligaments (Fig 4, C, Fig 7). This should not be diagnosed
Curr
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Diagn
Radiol,
November/December
1998
FIG 24. Stretched scapholunate ligament. Coronol T2*W demonstrates widening of the scapholunate interval (arrows) intact but stretched and attenuated scapholunate ligament.
FIG
23.
lntraosseous
images demonstrate scapholunate ligament along vidual
ganglion.
Axial
(A)
a dorsal ganglion cyst as well as an associated
and
coronal
(G) at the intraosseous
the radial aspect of the lunate (arrowhead). fasicles within the median nerve (arrow].
Note
(B)
T2*W
level of the component also
the indi-
as a tear unless the signal intensity is equal to fluid on T2W or GRE images. Similarly, the high signal intensity where portions of the scapholunate and lunotriquetral ligaments attach to articular cartilage rather than directly to bone should not be misinterpreted as tears (Fig 4, D and E, Fig 7).t1 Osseous
Pathology
Physeal
injuries
Injuries to the skeletally immature wrist may lead to abnormalities of the growth plate, metaphysis or epiph-
Curr
Probl
Diagn
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November/December
1998
image with an
ysis of the distal radius and ulna. Trauma to the physis (growth plate) can result in the formation of an osseous or fibrous bridge across the physis or slowing of growth in a portion of the physis, both of which can result in growth disturbance. 53 Extension of the injury to the metaphysis may result in a bone contusion or vertically oriented fracture. This may lead to thickening of the growth plate initially, with persistent cartilagenous foci found later within the metaphysis. These different findings have been described in competitive gymnasts.54>55 Physeal injuries can sometimes be detected on conventional radiographs. 56 However, MRI will demonstrate occult fractures and contusions as well as the presence of a bone or fibrous bridge. GRE-T2*W images demonstrate the low-intensitv d osseous or fibrous bridge against the high-signal-intensity cartilage of the physis. GRE sequences can also confirm the cartilagenous nature of the post-traumatic metaphyseal lucencies.54>55 Occult Bone Injuries Radiographically occult bone injuries are common causes of wrist pain. In a patient with recent wrist trauma and negative radiographs, a radionuclide bone scan is recommended as the next step in many imaging algorithms. Although it is extremely sensitive for detecting osseous injuries, bone scintigraphy suffers from a lack of specificity, poor spatial resolution, exposure to ionizing radiation, long examination time (3 to 4 h), and the possibility of a false/negative scan in the acute setting (less than 48 h).57
207
FIG
(A)
Scapholunate and sag&al
scapholunate
ligament
T2”W
25.
ligament tear Tl W (B) images with
widening tear
(arrowhead). Note also the large (arrow). A DISI pattern is seen on lunate
(L). F, Flexor
with DlSl deformity. Coronal demonstrate disruption of the of the scapholunate interval of the triangular fibrocartilage
the sagittal
view
with
dorsal
tilt of the
tendons.
MRl is at least as sensitive as bone scintigraphy for detecting occult osseous injuries58 and offers the additional advantages of excellent spatial resolution with direct demonstration of associated soft tissue injuries, a lack of ionizing radiation, and a short examination time. The cost of MRI has been considered a disadvantage. However, because of its exquisite contrast and spatial resolution, even a limited imaging protocol is highly accurate for detecting osseous injuries.59 In cases of suspected occult osseous injury, we employ a limited “trauma screening” wrist protocol consisting of coronal Tl and FSE-IR sequences that can be offered at a substantially lower charge than a bone scan or standard MR examination. Bone contusions and fractures in the wrist produce typical signal abnormalities in the marrow. A contusion appears as an amorphous, geographic area of abnormal signal intensity. The associated hemorrhage and edema is of low signal intensity on TlW images and high signal intensity on T2W images (Fig 13).60 These changes are especially conspicuous on FSE-IR and fat-saturated FSE-T2W images. 61 An occult fracture is identified as a linear focus of signal abnormality within the marrow edema that is low signal intensity on TlW images and may be either of low or high signal intensity on any type of T2W image (Fig 14).
208
The scaphoid is the most commonly fractured carpal bone and is the second most common wrist fracture after injuries to the distal radius. 62 Early detection and appropriate treatment of a scaphoid fracture is critical because of the relatively high incidence of associated complications that include delayed fracture union or nonunion and avascular necrosis (AVN) of the proximal fragment.63 An average of 16% of scaphoid fractures are not seen on initial radiographs. 64 Accordingly, in most cases of suspected scaphoid fractures, if initial films are negative, the patient is placed in a splint and follow-up radiographs are obtained in 1 to 2 weeks. This results in additional costs related to the follow-up visit and time off of work, and in most series only 15% to 25% of these patients are found to have a proven fracture on follow-up radiographs.64 MRI is highly accurate in detecting and delineating fractures of the scaphoid63,64 and other ossesous structures of the wrist (Figs 15, 16).65 In most cases a frac-
Curr
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November/December
1998
FIG 27. SLAC the scapholunate
wrist. Coronal T2*W image demonstrates disruption of ligament with proximal migration of the capitate and
loss of articular cartilage in the radiocarpal space also the attenuation of the triangular fibrocartilage loss of articular
FIG
26.
Scaphoid
fracture
with
associated
DISI
deformity.
Sag&al
Tl W images (A, B) demonstrate non-united scaphoid fracture (arrow). The adjacent sagittal image demonstrates volar translation and dorsal tilt of the lunate (L) compatible with the DISI pattern. F, Flexor tendons;
P, proximal
pole;
D, distal
pole.
ture line will be evident, but cases of diffuse edema without a fracture line have been reported in patients who were shown to have a true scaphoid fracture on
C&rr Probl
Diagn
Radiol,
November/December
1998
FIG
28.
cartilage
Kienbock’s
in the distal
disease
with
radioulnar
VP3
pattern.
(small arrows). (open arrow) joint
Note and
(arrowhead).
Sagitta(
TlW
image
demonstrates diffuse low signal intensity within the lunate (L) consistent with AVN. Note the dorsal displacement and volar tilt of the lunate and volar displacement of the capitate relative to the radius.
follow-up radiographs. 63 With healing, the marrow signal abnormality tends to fade and becomes isointense with adjacent marrow fat.@
209
gical planning. This has been accomplished with varying degrees of success by using radiographs, tomography, bone scan, and intraoperative inspection for punctate bleeding in the viable bone.67 Normal marrow signal intensity on TlW images is highly predictive of viability.68>69 Conversely, low signal intensity on TlW and T2W images is a specific sign of necrosis (Fig 17).68 The pattern of low signal intensity on T 1W images and high signal intensity on T2W images is less specific because it could be related to traumatic bone marrow edema or ischemic change (Fig 18).
FIG
29.
Triangular
fibrocartilage
perforation.
Coronal
demonstrates a small perforation in the triangular cent to its radial attachment (arrow).
FIG
30.
Partial
tear
of the triangular
image demonstrates increased extending into the undersurface
arrow)
without
evidence
fibrocartilage.
signal intensity of the triangular
of a full-thickness
T2*W
fibrocartilage
Coronal
equal to that fibrocartilage
image adia-
T2’W of fluid
(curved
tear.
AVN Because of the tenuous blood supply of the proximal pole of the scaphoid, AVN is a common fracture complication and is often an important contributory factor in the development of nonunion. Assessment of the viability of the proximal fragment is important for sur-
210
Kienbiick’s Disease The exact etiology of AVN of the lunate (Kienbock’s disease) is uncertain, but possible factors include repetitive trauma, acute fracture, lunate geometry, variations in lunate vascular&y, and ulnar minus variance (which results in increased shear forces on the lunate).70,71 This disorder affects men much more commonly than women. The patient typically describes wrist pain that worsens with activity and improves, at least temporarily, with rest. More than 95% of affected patients are involved in manual labor.72 Several anatomic features of the lunate make it especially vulnerable to the development of AVN. Its blood supply is extremely tenuous, with small nutrient arteries entering at only two sites along its dorsal and volar surfaces.73 Limited arterial anastomoses within the lunate result in much of its proximal and distal poles being fed by end arteries. Additionally, its central position in the carpus subjects it to high compressive forces that are even more pronounced when there is negative ulnar variance.r6 Kienbock’s disease follows a predictable sequence. Initially, the osseous changes are confined to the lunate. With progression, lunate fragmentation and collapse occur, ultimately leading to scapholunate dissociation, proximal migration of the capitate, and the development of diffuse degenerative changes.74 Treatment is based on the stage of the disease. Therefore, if the disease is detected at an earlier stage, therapy can then be aimed at preventing lunate collapse and subsequent degeneration and instability.69 Unfortunately, the disease is often clinically silent in its early stages, apparently because of a relative paucity of nerve endings along the lunate, and radiographic changes may not be detected until relatively late in the process, when the damage is irreversible.75>76 Four radiographic stages have been described. Stage I: Normal radiographs. Stage II: Increased density in the
Curr Probl
Diagn
Radiol,
November/December
1998
FIG 3 1. Injuries to the ulnar aspect of the triangular fibrocartilage and adjacent extensor carpi ulnaris tendon sheath. Coronal (A) and axial (6) T2*W images reveal disruption of the triangular fibrocartilage at its ulnar attachment (arrow) with associated extensor carpi ulnaris tendonopathy and probable tendon sheath disruption (arrowhead). E, ECU tendon; U, ulnar styloid.
lunate. Stage III: Lunate collapse, without (IIIA) or with (IIIB) fixed scaphoid rotation and scapholunate dissociation. Stage IV: Generalized carpal degeneration.74 MRI is the most-sensitive imaging modality for detecting osteonecrosis and is more specific than bone scintigraphy. Abnormal marrow signal intensity is present on MR images in stage I disease. Decreased signal intensity on TlW and T2W images is diagnostic (Fig 19).76-78 Increased signal intensity on T2W images suggests an earlier stage of the disease.78 Typically the entire lunate is involved; however, focal
Curr Probl
Diagn
Radio&
November/December
1998
FIG 32. Thirty-nine-year-old man with distal radial fracture, dorsal subluxation of the distal radioulnar joint, and tendonopathy or partial tears of the extensor carpi ulnaris tendon. Axial T2*W images demonstrate disruption of the volar radioulnar ligament (curved arrow) and associated subluxation of the distal radioulnar joint (D). Note also the subluxation and partial tear/tendonopathy of the extensor carpi ulnaris tendon at the level of the distal ulna [arrow) and proximal carpal row (open arrow), as well as fluid surrounding the extensor carpi radialis tendons (arrowheads) that is compatible with tenosynovitis.
AVN can occur (Fig 20). To avoid over-reading small, non-necrotic foci within the bone as AVN, some people believe that AVN should not be diagnosed unless at least one half of the bone is involved.76 Favorable MRI signs suggesting revascularization include diffuse or focal increased signal intensity on T2W images as well as restoration of normal marrow signal intensity overall. Patients with these signs tend to have more-favorable outcomes after surgery.78 AVN can rarely involve other carpal bones and may occur from prior trauma, steroid use, or on an idiopathic basis (Fig 21).7g
211
FIG rum
33. Flexor digitorum tendons in the carpal
FIG
34.
Twentyeight-year-old
donopathy the flexor
involving digitorum
FIG
Thirty-three-year-old
35.
tenosynovitis. tunnel (open
man
Axial
arrows)
with
wrist
the extensor carpi ulnaris tendons in B is compatible
man
with
distal
Tl W (A) and fast spin echo compatible with tenosynovitis.
pain
(arrow) with
radial
after
injury.
Axial
and extensor mild tenosynovitis.
fracture
and
T2*W (B) images demonstrate diffuse edema within the distal radius the abductor pollicis longus and extensor pollicis brevis tendons with
212
TlW
T2W (B) axial images demonstrate (Same patient as in Fig 49.)
(A)
and
T2*W
(B) images
digiti minimi (open arrow) Note also the enlarged
associated
tendonopathy
fluid
reveal
tendons. Slightly median nerve.
of the first
that is compatible with the patient’s peritendinous edema (arrows).
Curr
Probl
dorsal known
Diagn
surrounding
partial
tears
increased
compartment. fracture
Radiol,
the flexor
and/or
signal
Axial
digito-
severe
intensity
Tl W
ten-
around
(A)
and
as well as ill definition
November/December
1998
of
FIG 36. De Quervain’s tenosynovitis. saturated TlW axial (B) and coronal
Axial
TlW
(C)
images
image obtained
(A)
and
fat-
after
the
administration of intravenous gadolinium demonstrate thickening and striking enhancement of the tendon sheaths of the abductor pollicis longus and extensor pollicis brevis tendons (open arrows).
strate associated TFC pathology. MRI is advantageous as compared with other imaging techniques because it provides early evidence of the syndrome by demonstrating signal abnormality in the subchondral marrow of the lunate and/or head of the ulna before radiographic changes are apparent (Fig 22).80 MRI also allows for simultaneous, noninvasive evaluation of the TFC. lntraosseous
Ulnar impaction The ulnar impaction syndrome is the result of chronic abutment of the distal ulna on the lunate, causing cartilage loss, degenerative subchondral bone changes, and tears of the intervening TFC.*O There is a strong relationship between the ulnar impaction syndrome and ulna plus variance because of the increased forces transmitted across the ulnar aspect of the joint with that anatomic configuration. Positive ulnar variance occurs as an anatomic variant or may develop as a result of an impacted radial fracture. Ulna plus variance and changes of the ulnolunate impaction syndrome can be diagnosed on postero-anterior radiographs, but associated subchondral lucencies in the lunate and ulnar head are not evident radiographically until late in the process. Arthrography can demon-
Curr
Probl
Diagn
Radiol,
November/December
1998
Ganglia
Intraosseous ganglia are focal cystic lesions within subchondral bone that are composed of a dense fibrous wall and mucoid fluid. They may occur purely within the bone or result from the intraosseous extension of a soft tissue ganglion cyst. 81 Once thought to be rare, these were found to be responsible for chronic wrist pain in 4% of patients in a large series.82 MR imaging can demonstrate radiographically occult intraosseous ganglia. These appear as well-circumscribed foci of low signal intensity on TlW images and high signal intensity on T2W images of any kind (Fig 23). If other causes of wrist pain such as carpal instability, intraosseous ligament tear, or TFC pathology have been ruled out, a radionuclide bone scan can provide supportive evidence of a symptomatic ganglion if abnormal uptake is identified at the site of the cystic lesion.82
213
FIG T2*W tendon
37.
Extensor
(B) images with mild
presented
with
carpi
ulnaris
demonstrate associated
painful
tendon
subluxation.
subluxation tenosynovitis
clicking
in the wrist
Axial
Tl W
(A)
and
of the extensor carpi ulnaris (arrows) in this patient who after
trauma. FIG
Ligamentous
Pathology
Biomechanics The proximal carpal row functions as an intercalated segment between the distal radius and distal carpal row. l9 These segments are connected and stabilized by ligamentous structures. Without this ligamentous support, the geometry of the carpal bones would lead to a zigzag pattern of collapse during axial loading of the wrist. The scaphoid forms a bridge between the proximal and distal carpal rows and thereby plays an important role in carpal stability.19 The natural tendency of the lunate to dorsiflex under an axial load is countered by its attachment to the scaphoid (which tends to palmarflex) via the SLL. Similarly, the tendency of the triquetrum to dorsiflex is countered by its attachment to the lunate (and scapholunate unit) via the LTL.t9 Carpal instability is defined as a loss of the normal alignment of the carpal bones, and it occurs when there is disruption of these ligamentous
214
38.
injury carpal median proximal
Fifty-one-year-old
2 weeks previously. tunnel demonstrates
woman
with
persistent
wrist
pain
after
Axial T2*W image (A) just proximal to the increased signal intensity within an enlarged
nerve (curved arrow). An axial Tl W image at the level of the carpal tunnel (B) reveals signal abnormality within the tri-
quetrum (I’) compatible with contusion and/or occult ment of the median nerve (curved arrow), and bowing naculum,
compatible
with
post-traumatic
median
nerve
fracture, enlargeof the flexor retineuritis,
constraints.83 Ultimately, carpal instability can lead to carpal collapse and early degenerative changes.t9 Imaging A conventional radiograph should be the first imaging study performed in patients with suspected carpal instability. Stress views and/or video fluoroscopy may reveal an instability pattern that may not be present on routine images. 84 Ligamentous perforation or rupture can be identified with arthrography when abnormal communication of contrast is identified between compartments. However, the exact site of the perforation may be difficult to determine and the clinical significance of an
Curr
Probl
Diagn
Radiol,
November/December
1998
arthrographic abnormality is often uncertain because of the frequency of asymptomatic perforations.85 MRI is a useful adjunct to conventional radiographs because of its ability to directly display the intrinsic and extrinsic ligaments and to identify which segments of the ligaments are abnormal. The most reliable MRI sign of ligamentous disruption is a discrete discontinuity of the ligament with increased fluid intensity signal traversing the defect on T2W images. Other MR signs of ligament injury include being unable to identity the ligament on at least two contiguous images, significant distortion of ligamentous morphology, or an elongated ligament with widening of the intercarpal joint (Fig 24).86 Scapholunate Instability Instability of the scapholunate joint (rotary subluxation of the scaphoid, scapholunate dissociation) is the most-common type of carpal instability.19 The exact degree of injury to the SLL needed to result in instability is controversial. Some believe that a tear involving the dorsal segment of the ligament is enough to result in instability,l* whereas others contend that the entire ligament must be torn or that the palmar radiocarpal ligaments must be injured in addition to the SLL before instability occurs.87 A perforation of the central segment of the SLL doesn’t result in instability.t2 Scapholunate instability occurs when stretching or tear of the SLL dissociates the lunate from the scaphoid and frees the lunate to displace in a volar direction and tilt dorsally. The scaphoid tilts in a palmar direction (rotatory subluxation), and the scapholunate angle increases to greater than 60 degrees. These changes result in the dorsal intercalated segmental instability (DISI) pattern that can be detected on a lateral radiograph or sagittal MR images (Fig 25). Unstable scaphoid fractures can result in a similar appearance because the distal fracture fragment tilts in a palmar direction after it “dissociates” from the proximal fragment and lunate which tilt dorsally, even though the SLL remains intact (Fig 26).19 If left untreated, scapholunate dissociation can lead to the development of the scapholunate advanced collapse pattern (SLAC wrist). In this pattern, the capitate migrates proximally between the scaphoid and lunate with the development of rapidly progressive degenerative changes, most often involving the lunate-capitate and radiocarpal spaces (Fig 27).8” Variable accuracy rates have been reported in the literature for detecting SLL tears with MR imaging. In
Curr Probl
Diagn
Radiol,
November/December
1998
Fig
39. PD/TH.
“Y
images
Bowing
I
demonstrate
ratio.
The
bowing
, 11tunnel. Coronal an ununited scaphoid
ganglion cyst eroding into the trapezoid or tendons in the carpal tunnel.
ratio
is calculated
by dividing
Tl W (A) and axial T2*W (B) fracture (black arrows] and a (white
arrows),
deep
to the flex-
215
FIG 41. Prominent demonstrates a large carpal
vessel vessel
in the carpal tunnel. (v) abutting the flexor
Axial T2’W image tendons deep in the
tunnel.
the two largest series that evaluated SLL tears, sensitivity, specificity, and accuracy ranged from 50% to 90%, 90% to lOO%, and 77% to 90%, respectively, when arthrographic and/or surgical findings were used as the standard of reference.13,s6 As with arthrography, the MR findings must also be viewed with the understanding that not all SLL perforations produce symptoms and that degenerative perforations most often involve the thin, central portion of this ligament. Therefore identification of involvement of the dorsal or volar segments on coronal images may prove to be more predictive of a significant lesion, but this has not been documented in the literature.
FIG
42.
Axial strate
Tl W (A) and fast spin echo
also
the severed the palmar
focal
after
flexor
retinaculum
release.
of the flexor
tendons
which
also
demon-
fluid compatible with tenosynovitis. Focal high sigthe enlarged median nerve (arrowhead) is compati-
nerve
injury.
Instability
Disruption of the LTL is the second-most-common ligamentous cause of carpal instability.19 This allows the triquetrum to tilt dorsally while the lunate, which is still attached to the scaphoid via the SLL, tilts in a volar direction.88 This results in the volar intercalated segmental instability (VISI) pattern in which the scapholunate angle narrows to less than 30 degrees (Fig 28). There is a strong association between tears of the triangular fibrocartilage and LTL tears.19 In general, the diagnosis of LTL tears with MR imaging has proved to be more difficult than for the SLL, probably because of its smaller size. In the two series mentioned previously, the sensitivity, specificity, and accuracy of MRI imaging for detecting LTL tears ranged from 50% to 56%, 45% to lOO%, and 49% to 90% respectively.13J6
216
ends
man,
inversion recovery (6) images demonof the flexor retinaculum (curved arrows). Note
displacement
strate peritendinous nal intensity within ble with
Lonotriquetral
Twenty-six-year-old
Extrinsic
I igaments
The normal MR appearances of the extrinsic carpal ligaments have been extensively described; however, the ability of MRI to diagnose tears of the extrinsic ligaments, and the clinical significance of these injuries, is not well established. As a result, we do not spend much time analyzing the extrinsic ligaments when interpreting MR studies of the wrist. Pathology of the TFC A number of conditions can result in ulnar sided wrist pain including TFC and/or LTL injury, triquetral avulsion fracture, pisotriquetral arthritis, subluxation or tendinitis of the extensor carpi ulnaris tendon, ulnar artery thrombosis, and ulnar neuropathy in Guyon’s
Curr Probl
Diagn
Radiol,
November/December
1998
FIG
44.
Twenty-four-year-old
gery with incomplete image demonstrates level of the hamate. compatible
FIG
43.
Forty-five-year-old
(A)
Axial TlW demonstrate
and absence
ment (curved (arrowheads).
arrow) Note
in a palmar
direction.
woman,
status
after
carpal
tunnel
Diagn
status
after
carpal
tunnel
median
nerve
surT2*W at the nerve
neuropathy.
release.
T2*W (B) images at the level of the pisiform (P) of the flexor retinaculum near its scaphoid attachas well as the residual portion of the retinaculum the enlarged median nerve (M) which is displaced
canal. Additionally, pain resulting from a radial sided disorder may be referred to this region.8g Palmer separated lesions of the TFC into degenerative and traumatic categories, and then created subdivisions based on the location of the lesion-specifically, whether it involved the radial or ulnar margin of the TFC.gO The location of a tear has therapeutic implications because of the vascular supply of the TFC.gl The peripheral 15% to 25% of the cartilage, along its ulnar margin, is well vascularized, and tears in this region may heal with nonoperative therapy. The remaining portions of the TFC (central and radial margins) are essentially avascular. As a result, perforations in these regions are usually debrided, although good results have been reported after operative reattachment of tears and/or avulsions involving the radial margin of the disk.92 MRI is highly accurate in diagnosing TFC injuries.13,86s9,93,g4 Tears or perforations in the central and radial portions of the disk are especially well demon-
Curr Probl
with
woman,
release of the flexor retinaculum. Axial intact flexor retinaculum (curved arrows) Note also the enlargement of the median
Radiol,
November/December
1998
FIG 45. Twenty-nine-year-old with fibrosis around the median absence of the flexor retinaculum
man, status after carpal tunnel release nerve. Axial Tl W image demonstrates at the level of the pisiform (P) with low
signal intensity scarring in the palmar subcutaneous The fibrosis extends deeper (black arrows) around nerve
fat (white an enlarged
arrow). median
(M).
strated (Figs 1.5, 22, 25, 29). Those near the ulnar styloid are less-accurately diagnosed because of the intermediate signal intensity normally present in this portion of the TFC and because post-traumatic synovitis or synovial proliferation in the prestyloid recess can mimic a tear.8g,95 MRI is also able to demonstrate a partial tear or irregularity along the undersurface of the TFC that would be missed at arthroscopy when using standard radiocarpal portals (Fig 30).89 It is important to report the exact location of the tear in the TFC. Tears in its central portion may not account for the patient’s symptoms because the incidence of degenerative, often asymptomatic perfora-
217
Traumatic tears of the TFC are often associated with injuries of adjacent structures. MRI is able to demonstrate these injuries, which include disruption of the ECU tendon sheath and partial or complete tear of the LTL (Fig 31). to1 The depiction of associated injuries of the ulnolunate and ulnotriquetral ligaments is less reliable.94 The disruption of the volar or dorsal radioulnar ligaments is associated with the instability of the DRUJ. MR can demonstrate subluxation and/or dislocation of the DRUJ in the axial plane of imaging,lo2 but it also provides excellent depiction of the radioulnar ligaments, TFC, and other important associated structures (Fig 32). Traumatic disruption of the ECU tendon sheath can result in subluxation of the tendon at the level of the ulnar head and related tenosynovitis. The tendon generally subluxes or dislocates over the styloid process in an ulnar (medial direction) rather than lying in the normal groove on the dorsum of the ulna. The subluxed tendon and signs of associated tenosynovitis are best seen on axial MR images at the level of the distal ulna.to3>lo4 “Dynamic” MRI is performed by imaging the wrist while it is moved from extreme radial to ulnar abduction with a mechanical device. This has been used to detect cases of ulnocarpal impaction not detectable on static images, including cases of impaction related to instability of the ulnar attachments of the TFC.to5 However, this technique is not a part of routine clinical imaging. Tendon FIG 46. Fifty-year-old Tl W [A) and T2*W the hook of the (curved arrow).
man with history of ulnar nerve palsy. Axial (6) images reveal a ganglion cyst (C) adjacent to
hamate,
displacing
the
ulnar
neurovascular
bundle
tions of the central portion of the TFC increases with age. More than 50% of patients over 60 years of age will demonstrate this type of perforation.96 Increased signal intensity can be seen within the TFC on MRI in up to 50% of asymptomatic subjects.97,98 This is probably due in large part to the degenerative changes found in the TFC with advancing age, similar to the men&al degeneration observed in the knee.98 Kang et al found that degenerative changes within the TFC demonstrate intermediate to high signal intensity on TlW images but are of lower signal intensity on T2W images. Conversely, acute tears and perforations demonstrate high signal intensity, similar to fluid, extending through the substance of the TFC on T2W images.99,‘00
218
Pathology
The tendons of the wrist and hand are commonly affected by pathology ranging from tenosynovitis to degeneration to tears. Common etiologies include inflammatory arthritis and chronic repetitive trauma from overuse. Tendons demonstrate low signal intensity on all MR sequences with the exception of the magic angle effect described previously. Tendons may show slightly higher signal intensity near osseous insertions. The tendons of the wrist are best evaluated on axial images. A small amount of fluid in a tendon sheath can be seen in one or more of the dorsal compartments in normal subjects.lo6 Distention of the sheath with fluid completely surrounding the tendon is diagnostic of tenosynovitis, which may be sterile or purulent (Fig 33). Stenosing tenosynovitis is diagnosed when septated and/or loculated fluid is identified within the sheath. With chronic tenosynovitis, the signal intensity of the surrounding material may be more hypointense because of the development of fibrosis. lo4
Curr
Probl
Diagn
Radiol,
November/December
1998
Tendon degeneration or partial tears result in enlargement of the affected tendon, and increased signal intensity is often identified within its substance on short echo time (TE) images (Fig 34).lo3 A partial tear represents incomplete disruption of the tendon’s fibers and may appear as a thickened or attenuated tendon or as a discrete focus of increased signal intensity within the tendon on Tl, T2, or GRE images. Absence of a tendon within its sheath on axial images is diagnostic of complete rupture, and MRI can be used to preoperatively assess the degree of separation between the ends of the disrupted tendon. DeQuervain’s
Syndrome
Tenosynovitis of the abductor pollicis longus and extensor pollicis brevis tendons in the first dorsal compartment (DeQuervain’s syndrome) is often idiopathic but is also associated with pregnancy, repetitive lowgrade injury, and direct trauma (Fig 35). It is more common in females and typically manifests with swelling and tenderness over the radial styloid.lo4 Clinical diagnosis is usually straightforward, but occasionally the findings are subtle and the syndrome may be indistinguishable from a scaphoid fracture, flexor carpi radialis tenosynovitis, or degenerative arthritis of the first carpometacarpal joint.to7 Thickening of the tendons and peritendinous edema are the most-reliable MRI findings (Fig 36).lo8
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG Tl W
47.
(A)
Schwannoma and
of the deep
fast spin echo
a rounded mass (H). Homogeneous
inversion
branch recovery
of the ulnar
nerve.
(B) images
Coronal
demonstrate
(M) along the ulnar aspect of the hook of the hamate high signal intensity on the inversion recovery image
suggests a cyst. However, a fat-saturated, axial Tl W image obtained after the intravenous administration of Gd-DTPA (C) demonstrates relatively homogeneous enhancement compatible with a solid mass. Biopsy revealed
this
to be a schwannoma
of the deep
branch
of the ulnar
nerve.
ECU Tendon The ECU tendon, in the sixth dorsal compartment, is the second-most-common extensor tendon involved with tenosynovitis. This often occurs as a result of repetitive subluxation of the ECU tendon after disruption of its sheath (Fig 37). lo4 Because increased signal
219
FIG
48.
Neural
fibrolipoma
fast spin echo inversion enlargement and tortuosity enlarged, low-signal-intensity trating high-signal-intensity
of the median recovery (B) of the median neuronal
nerve.
Axial
Tl W (A) and
images demonstrate nerve (arrows). In A, fasicles
surrounded
marked note the
by the infil-
fat.
intensity within the ECU tendon may occur in asymptomatic patients, the diagnosis of tendon degeneration or partial tear should be reserved for cases where MRI shows enlargement of the tendon and/or definite peritendinous edema and/or fluid. Ofher Tendons Tendon pathology is also commonly seen in the extensor car-pi radialis, flexor carpi radialis, and flexor car-pi ulnaris tendons. Tenosynovitis of the flexor digitorum tendons is a common cause of carpal tunnel syndrome. lo4 Nerve
Pathology
Compressive
Neuropathies
Carpal Tunnel Syndrome. Carpal tunnel syndrome (CTS) results from compression of the medial nerve within the carpal tunnel. It is the most-common peripheral compressive neuropathy. Affected patients typically present with pain and paresthesias in thumb, index finger, long finger, and radial half of the ring finger. Symptoms are usually worse at night.lo9 The etiology of CTS may be multifactorial. Causes include osseous abnormalties (fracture, callus formation, carpal malalignment), soft tissue changes that narrow the tunnel (mass, hematoma, tenosynovitis, anomalous muscle), and systemic processes (pregnancy, amyloidosis, etc).r lo Space-occupying lesions are more commonly found in patients, with unilateral symptoms.rl’ Some
220
patients suffer from dynamic CTS, which is a cumulative trauma disorder related to repetitive, usually workrelated, microtrauma. Symptoms in these patients typically abate with rest. lo9 The diagnosis is usually made through a combination of clinical findings and nerve conduction studies. MRI is not used as a primary diagnostic modality in this setting, but it has been advocated to detect any underlying causative factors and as a useful adjunct when nerve conduction studies are equivocal.l12 MRI findings in patients with CTS are best seen on axial images and include swelling of the median nerve (best assessed at the level of the pisiform) (Fig 38), flattening of the median nerve, and excessive pahnar bowing of the flexor retinaculuml10 (best assessed at the level of the hamate). The degree of bowing is expressed as a “bowing ratio” (Fig 39). To calculate this ratio, a line is drawn from the triquetrum to the hook of the hamate on an axial image (length = TH). The distance from this line to the flexor retinaculum (palmar displacement = PD) is divided by the length TH.41Ratios in normal subjects range from 0% to 15% (mean =
Curr Probl
Diagn
Radiol,
November/December
1998
FIG 49. Dorsal T2*W (C) images scaphoid (S) and appearance, and
ganglion cyst. Sagittal Tl W (A), T2*W (B) and axial reveal a lobulated, septated mass (C) just dorsal to the scapholunate location are
ligament. classic for
Its signal a dorsal
intensity, ganglion
overall cyst. I,
Lunate.
FIG 50. Volar high-signal-intensity the wrist
5.8%) and from 14% to 26% (mean = 18.1%) in patients with CTS. 1lo Increased signal intensity within the median nerve on T2W images has also been described in patients with CTS, but this finding is subjective.“’ MR can also demonstrate any contributory flexor tenosynovitis or space-occupying mass within the carpal tunnel (Figs 40 and 41). In patients with activi-
Curr
Probl Diagn
Radiol,
November/December
1998
just deep
ganglion cyst. Axial T2*W ganglion cyst (C) along to the flexor
carpi
radialis
image demonstrates small the volar, radial aspect of tendon
(curved
arrow).
ty-related symptoms (dynamic CTS), MR imaging before and after exercise has been found to accentuate abnormal MRI findings. 1I3 When conservative treatment fails, release of the flexor retinaculum via an open or endoscopic technique is usually performed in an attempt to increase the volume of the carpal tunnel. Common postoperative MRI findings include an increase in the overall volume of the carpal tunnel with palmar displacement of the flexor tendons, increased fat content in the tunnel or along its palmar aspect, and the development of hypointense scar tissue, typically along the ulnar aspect of the carpal tunnel. 1l4 MRI findings compatible with complete release of the flexor retinaculum include identification of a sur-
221
FIG 52. Giant cell tumor T2W image demonstrates thenar musculature Note the multiple ible with
FIG 5 1. Pisotriquetral arthritis and associated ganglion cyst. Tl W (A) and axial T2*W (B) images demonstrate narrowing pisotriquentral degenerative
Sagittal of the
joint with a small osteophyte (arrow) compatible with arthritis. Note also the associated ganglion cyst or syn-
ovial outpouching aspect of the wrist
arising from the pisotriquetral (C). P, Pisiform; T, triquetrum.
joint,
along
Coronal mass
fast spin echo (arrows) in the
with extension into the distal wrist (curved areas of low signal intensity within the mass,
urrows). compat-
hemosiderin.
Postoperative failures may be attributed to a number of causes, the most common of which is incomplete release of the flexor retinacu1um.l l5 MRI findings suggestive of an anatomic basis for recurrent symptoms include identification of an intact portion of the flexor retinaculum (Fig 44), the development of low signal intensity fibrotic scarring around the median nerve (Fig 45), and proximal swelling of the nerve.l15 MR imaging may also reveal a persistent or recurrent mass lesion within the carpal tunnel or the development of a median nerve neuroma. Ulnar Tunnel Syndrome. The ulnar nerve may become compressed along the course of Guyon’s canal. Etiologies include carpal ganglion cysts or other masses, fracture of the hamate, or repetitive occupational trauma to this region.lo7 The course and status of the nerve as well as any adjacent masses can be assessed on axial images (Fig 46).‘16>r17
the ulnar
gical defect along the entire course of the retinaculum, palmar displacement of the flexor tendons through severed margins of the retinaculum, and absence of the retinaculum (Figs 42 and 43).
222
of the tendon sheath. a large, heterogeneous
Neural
Tumors
Nerve Sheath Tumors. Benign nerve sheath tumors, (schwannoma and neurofibroma) occur in the hand and wrist, with schwannomas having a predilection for involving the ulnar nerve. 1l8 These usually appear
Curr Probl
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1998
FIG 53. Soft tissue hemangioma. Axial TlW (A) and fast spin echo T2W (B) images demonstrate CI lobular mass in the volar soft tissues of the forearm at the level of the distal radioulnar joint. Note the scattered areas
of fat within
the lesion
demonstrating
Tl W image and the homogeneous mass on the T2W image. Punctate, ible with
phleboliths
(open
high
signal
intensity
on the
high signal intensity throughout the low-signal-intensity foci are compat-
arrows).
as a fusiform mass related to a neurovascular bundle that is isointense or slightly hyperintense to muscle on TlW images and of high signal intensity on T2W variable degrees of images. They demonstrate enhancement after contrast administration (Fig 47).11s Although their MR imaging appearance is often non-specific, two MR findings have been described that may help in diagnosing these lesions. The fast, designated the “split fat” sign, describes the peripheral rim of fat often seen surrounding the lesion that is thought to relate to the fat that normally surrounds the neurovascular bundle, the site of origin of these lesions.l18 The “target sign,” described in neurofibro-
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG
(A)
54.
Rheumatoid
arthritis.
Posteroanterior
radiograph
demonstrates diffuse osteoporosis without definite Tl W (B) and T2’W (C) images demonstrate synovial small erosions of the third, fourth, and fifth metacarpals
of the wrist erosion. Axial pannus (P) and (3, 4, 5).
223
FIG
55.
Rheumatoid
arthritis.
PA radiograph
of the wrist
(A) demon
strates small erosions of the capitate (arrowheads). Axial Tl W (6) and inversion recovery (C) images demonstrate apparent tenosynovitis of the extensor digitorum tendons (curved arrows). ed Tl W image obtained after the intravenous
However, a fat-saturatadministration of Gd-
DTPA (D) reveals markedly enhancing pannus around the tendons as well as in the distal radioulnar joint (small arrows]. Note also minimally enhancing brevis image
cent enhancing
mas, refers to central low signal intensity and peripheral high signal intensity on T2W images, which probably correspond to central fibrosis and peripheral myxomatous tissues, respectively.l19 It is impossible to differentiate benign from malignant nerve sheath tumors with MR imaging, but signs suggestive of malignancy include large size (>5 cm), rapid growth, ill-defined borders, and signal heterogeneity.’ l8
224
pannus
between
the extensor
tendon (long arrow). Sagittal (E) demonstrates small erosion pannus
(open
carpi
fat-saturated of the ulnar
radialis
longus
and
Tl W post-contrast head (u) with adia-
arrow).
Neural Fibrolipoma. The benign neural fibrolipoma (also known as fibrolipomatous hamartoma of nerve) is a lesion that most often arises in and causes marked enlargement of the median nerve. Initially, the lesion may be asymptomatic, but patients may go on to develop signs and symptoms of nerve compression.120 In 66% of cases there is associated macrodactyly
Curr
Probl
Diagn
Radiol,
November/December
1998
FIG 56. Rheumatoid arthritis. Axial T2*W image demonstrates pannus in the distal radioulnar joint (asterisk). Additional pannus displaces the extensor carpi ulnaris tendon (Ej. Note also the tenosynovitis involving the first dorsal compartment (arrow).
FIG
55
continued
(macrodystrophia lipomatosa).lls Pathologi-tally this lesion results from infiltration of the nerve by fibrous and fatty tissue. The lesion extends along the expected course of the median nerve and demonstrates a distinctive MRI appearance. It is seen as a serpiginous mass composed of tubular low-signal-intensity structures (probably corresponding to nerve fascicles surrounded by epineural and perineural fibrosis) within a background of high signal intensity fat (Fig 49).120 The differential diagnosis includes an intraneural lipoma, traumatic neuroma, and vascular malformation. 120 Masses The most common mass involving the wrist is the ganglion cyst,121 a fibrous walled structure containing thick, mutinous fluid. These can arise from tendon sheath or synovial tissue from any site. Approximately 60% to 70% are found along the dorsum of the wrist at the level of the scapholunate joint (Fig 49). A small synovial pedicle frequently extends through the dorsal fibers of the scapholunate ligament. Erosion of the ganglion cyst into the radial aspect of the lunate is common (Fig 23). Twenty percent of ganglia arise in the volar soft tissues between the flexor carpi radialis and abductor pollicis longus tendons (Fig 50).122
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Probl
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1998
Although dorsal lesions can be diagnosed with a targeted ultrasound examination,122>123 the ability to demonstrate deeper lesions and other osseous or soft tissue pathology is a distinct advantage of MRI (Fig 5 1).124 A ganglion cyst is a well-circumscribed, low-signalintensity mass on TlW images that demonstrates homogeneous high signal intensity, often with low-signalintensity septations, on T2W images because of its fluid content. It may display a more-heterogeneous signal if complicated by hemorrhage or infection. Gd-DTPA administration is helpful to differentiate a ganglion cyst from other solid masses that demonstrate similar signal characteristics, such as nerve sheath tumors (Fig 47). A ganglion cyst should not demonstrate central enhancement on post-gadolinium images, although enhancement of internal septae may be identified.125 The second-most-common soft tissue mass of the hand and wrist in most series is a giant cell tumor of the tendon sheath.t21 This is a localized, extraarticular form of pigmented villonodular synovitis (PVNS), a hyperplastic synovial process of unknown etiology. The characteristic MR finding of areas of low signal intensity on both TlW and T2W images is related to hemorrhage and resulting hemosiderin deposition within the lesion (Fig 52).126 Benign lipomas are recognized by their characteristic MR signal intensity that parallels fat on all sequences. Most are well circumscribed, but these can appear infiltrative, especially if compressed between tissue planes or if they arise within a muscle.126
225
The MR appearance of a soft tissue hemangioma is also relatively specific. These are usually isointense to muscle on TlW images, often containing some areas of high-signal-intensity fat. On T2W images, they appear as a lobulated mass, often displaying circular or serpentine areas of extremely high signal intensity corresponding to vascular channels and spaces (Fig 53).125 Associated phleboliths appear as punctate low-intensity foci. 126 These typically demonstrate prominent enhancement after the administration of intravenous Gd-DTPA.lr8 Synovial Rheumatoid
Pathology Arthrifis
Rheumatoid arthritis commonly affects the wrist. Detection of early disease is important to optimize therapy and limit the progression of joint destruction. It can be difficult to clinically differentiate proliferative synovitis (pannus) from a joint effusion in these patients,127J28 and radiographs are often normal in the early stages. MRI is able to directly demonstrate inflammed synovium. Pannus typically demonstrates low to intermediate signal intensity on TlW images and increased signal intensity on T2W images (Fig 54).127,12g>130Because these signal characteristics are similar to fluid, the intravenous administration of Gd-DTPA has proved useful for distinguishing between pannus and joint fluid.127-131 Gd-enhanced, fat-saturated TlW images provide superb contrast between the intensely enhancing synovial tissue and the low-intensity joint fluid and suppressed fat.132 Using this technique, MRI is able to demonstrate pannus and bony erosions earlier than is possible with conventional radiographs (Fig 55).133,134 In these early stages, areas of localized enhancement are more commonly seen, while diffuse synovial enhancement is characteristic of more advanced disease.135 Rheumatoid arthritis involves the extensor tendons of the wrist in 50% to 60% of patients, and clinical assessment of the degree of tendon involvement is often inaccurate. lo6 Involvement with pannus is usually manifest on MRI by tendon enlargement and inhomogeneous signal intensity (Fig 56). Fluid in the surrounding sheath is best seen on T2W images, whereas pannus within the sheath or tendon substance is best delineated on post-gadolinium images (Fig 55).lo6 Absence of the tendon within the sheath is consistent with a complete tear, but extensive infiltration of pannus within an intact tendon can mimic a rupture.lo6 MR can also be used to follow the progression or
226
regression of the disease. In a small group of patients who underwent serial MRI scans, those in remission demonstrated decreasing synovial proliferation and bone marrow edema, as well as no new erosions.136 Despite these features, MR is not currently used to diagnose or follow patients with rheumatoid arthritis in most centers. In our practice the two most-common indications for scanning these patients are (1) chronic wrist pain in a patient with negative radiographs, and no history of rheumatoid arthritis who is found to have the typical findings of pannus and erosions on MRI; and (2) a palpable mass in which MR is used to differentiate pannus from tenosynovitis. Summary MR imaging of the wrist has the unique capability of simultaneously demonstrating bone and soft tissue structures. Its exquisite sensitivity for detecting bone marrow edema makes it an ideal screening tool for diagnosing radiographically occult osseous injuries and areas of AVN. This, together with its ability to provide a comprehensive, non-invasive assessment of the ligaments, tendons, nerves, and components of the TFC make MRI a very powerful tool for evaluating patients with wrist pain of uncertain etiology. Its exact role in the work-up of these patients has not been entirely established, but with further advances in technology and the radiologist’s understanding of wrist anatomy and pathology, MRI is assuming a more central role in this clinical setting. REFERENCES 1. Larsen CF, Brondum V, Wienholtz G, Abrahamsen J, Beyer J. An algorithm for acute wrist trauma. J Hand Surg 1993;18B:207-12. 2. Aaron JO. A practical guide to diagnostic imaging of the upper extremity. Hand Clin 1993;9:347-58. 3. Chidgey LK. Chronic wrist pain. Orthop Clin North Am 1992;23:49-59. 4. Young VL, Higgs PE. Evaluation of the patient presenting with a painful wrist. Clin Plast Surg 1996;23:361. 5. Gilula LA, Yin Y. Imaging of the wrist and hand. Philadelphia: WB Saunders. 6. Kneeland JB. Technical considerations for MR imaging of the hand and wrist. Magn Reson Imaging Clin N Am 1995;3:191-6. 7. Stoller DW. The wrist. Semin Roentgen01 1995;30:265-76. 8. Constable RT, Gore JC. The loss of small objects in variable TE imaging: implications for FSE, RARE and EPI. Magn Reson Med 1992;28:9-24. 9. Anderson MW, Raghavan N, Seidenwurm DJ, Greenspan A, Drake C. Evaluation of meniscal tears: fast spin echo versus conventional spin echo magnetic resonance imaging. Acad Radio1 1995;2:209-14. 10. Elster AD. Gradient echo imaging: techniques and
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