- Email: [email protected]
Pitfalls in plain film diagnosis of cervical spine injuries: False positive interpretation
Surg Neurol 1986;25:381-92
381
Pitfalls in Plain Film Diagnosis of Cervical Spine Injuries: False Positive Interpretation K w a n g S. K i r n , M . D . , L e e F. R o g e r s , M . D . , a n d V i c t o r R e g e n b o g e n ,
M.D.
Department of Radiology, Northwestern University Medical School, and Northwestern Memorial Hospital, Chicago, Illinois
Kim KS, Rogers LF, Regenbogen V. Pitfalls in plain film diagnosis of cervical spinal injuries: false positive interpretation. Surg Neurol 1986;25:381-92.
Of 412 patients who were referred and admitted with acute cervical spine injury, 58 (14%) were subsequently found to have no fracture or dislocation when evaluated at our institution. These patients had no abnormal neurological findings or severe persistent pain in the neck. Their referral was based on false positive interpretations of radiographs of the cervical spine. The radiographs in these cases are analyzed, and conditions that had led to misinterpretation are described. The radiographic differential features from true acute traumatic injury are discussed. KEY WORDS: Cervical spine; Acute trauma; Radiographic diagnosis; False positive interpretation
The accurate detection of fractures of the cervical spine is essential in the management of acutely traumatized patients. Pitfalls in the diagnosis o f plain film of cervical spine injuries that lead to false negative interpretation have been well documented [2,12,16,22]. Equally troubling; however, is the occurrence of false positive diagnosis of cervical spine injuries because of misinterpretation of cervical radiographs. O f cases referred to the Midwest Spinal Cord Injury Unit of the Northwestern Memorial Hospital, a regional referral center, 14% were found to have had a false positive interpretation o f the radiographs o f the cervical spine as the basis for their referral. These patients had no abnormal neurological findings or severe persistent pain in the neck. It is the purpose of this report to evaluate and characterize the radiographic features that may be misinterpreted as acute traumatic cervical spine injuries.
Address reprint requests to: K.S. Kim, M.D., Department of Radiology, Northwestern Memorial Hospital, Superior Street and Fairbanks Court, Chicago, Illinois 60611.
© 1986 by Elsevier Science Publishing Co., Inc.
Materials and Methods Four hundred twelve patients with acute cervical spine injuries, excluding those from gunshot wounds, were admitted to the Midwest Spinal Cord Injury Unit of the Northwestern Memorial Hospital between January 1982 and September 1984. The vast majority of these cases were referred from outlying community hospitals. Fiftyeight patients (14%) who were referred and admitted with the diagnosis o f fracture or dislocation, or both, based on outside cervical films, were subsequently found to have no fracture or dislocation when evaluated at our institution. These patients had no abnormal neurological findings or severe persistent pain in the neck. It is this group of patients that is the subject of this report. All patients were evaluated with our routine cervical sp!ne series (anteroposterior, lateral, both oblique and open mouth Views) as well as flexion and extension lateral views. Polytomography was obtained in most cases (87.9%) and computed tomography (CT) in some (8.6%). The medical records and outside radiographs were reviewed in all cases. Subluxation was graded arbitrarily from 1 to 4 based on 2-ram increments. Atlantoaxial subluxations were graded from 1 to 4 based on 2-ram increments beyond the 3-ram normal limit.
Results The following conditions have led to false positive diagnosis of acute traumatic fracture or dislocation of the cervical spine.
Preexisting Degenerative Disease Twenty-three patients (39.6%) with degenerative joint disease were wrongly thought to have suffered an acute traumatic injury.
Subluxation. Subluxation accounted for 13 of cases. The patients' age and sex, the direction and of subluxation, the level involved, and the level sociated disk space narrowing are listed in Table
these grade of as1.
0090-3019/86/$3.50
Table
1. Cases w i t h Degenerative Subluxation
Number
Age (yr)
Sex
Level
1 2 3 4 5 6 7 8 9 10 11 12
65 74 79 60 75 96 85 66 42 46 74 60
F F F F M M F F M F F M
13
73
M
C5-6 C4-5 C3-4 C6-7 C-7-T-I C4-5 C-7-T-I C5-6 C3-4 C5-6 C3-4 C3-4 C4-5 C5-6 C2-3 C3-4 C4-5
Direction of subluxation
Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Retrolisthesis Retrolisthesis Retrolisthesis Retrolisthesis Anterolisthesis Anterolisthesis Retrolisthesis Anterolisthesis Retrolisthesis Retrolisthesis
Grade of subluxation
2 3 2 1 2 2 3 1 1 1 1 1 2
Disk space narrowing
C6-7 C5-6, C4-5, C5-6 C4-5, C5-6, C4-5, C5-6 C3-4 C5-6 C3-4, C5-6,
C6-7 C5-6 C5-6, C6-7 C6-7 C5-6, C6-7
C4-5, C5-6 C6-7
l
l 2 2
C3-4, C4-5, C5-6
Abbreviations: F, female; M, male. A
F i g u r e 1. A 74-year-old woman. (A) Lateral view of the cervical spine, showing degenerative anterolisthesis at C4-5, which was misinterpreted as a traumatic subluxation. There is a spur with a hooklike appearance (arrow) at the posterior aspect of the C5 facet. The disk spaces at the C5-6 and C6-7 levels are narrowed. (B) Lateral polytomogram of the facets showing the spur (arrow) from the posterior aspect of the C5 facet. The facet joint space is widened at the levd of anterolisthest~ but the joint surfaces remain parallel to each other.
B
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
383
A
In the cases with anterolisthesis, the forward slippage occurred from C2-3 to C - 7 - T - 1 levels. The amount of slippage varied from 1 to 6 mm. Every case o f anterolisthesis was associated with narrowing of the intervertebral disk spaces below or above the level of the slippage. The intervertebral disk space at the level of slippage was preserved in all cases (Figures 1-3). Various degrees of facet joint degeneration at the level of slippage were present in seven of nine cases. These degenerative changes were manifested by narrowing or widening of the joint space, sclerosis, spur formation, and a ribbonlike attenuation of the facets. The joint surfaces remained parallel to each other. These changes in the facet joints were best demonstrated by lateral polytomography (Figures 1-3). In the cases with retrolisthesis, the slippage occurred from C3-4 to C5-6 level. The degree of offset measured from 1 to 4 mm. The disk space was narrowed at the level of retrolisthesis in all cases. Degenerative changes such as end-plate irregularity, sclerosis, and spur formation were seen at the level of the retrolisthesis in all cases (Figures 3 and 4). In two cases, the presence of posterior osteophytes made evaluation of retrolisthesis difficult as it was not clear whether the posterior offset was a real finding,
Figure 2. An 85-year-old woman was referred with the diagnosis of a traumatic subluxation at C-7-T-1. (A) Midline lateral polytomogram, showing degeneratit~e anterolisthesis of C-7-T-1. The disk spaces above this level are narrowed, but the disk space at this level is maintained. (B) Lateral polytomogram of the facets showing thinning of the C-7 facet. The joint space at C-7-T-I is widened.
Platyspondylia. Degenerative flattening of the vertebral body (platyspondylia) was misdiagnosed as a compression fracture in three cases. The deformity was seen at either the C-5 or C-6 level, or both. Associated intervertebral disk space narrowing and degenerative spurring were present in all cases (Figure 5A and B). In one case, there was an associated vacuum p h e n o m e n o n in the disk spaces, and another case demonstrated ossification in the anterior longitudinal ligament at the C5-6 level. UncovertebraIJoint Degeneration. A horizontal lucent line seen in the lateral view over the vertebral body produced by uncovertebral joint degeneration was mistakenly diagnosed as a linear fracture in two cases. This lucency was seen over C-3 in one case and C-4 in the other case. Both cases demonstrated marked degenerative changes at multiple levels. The corresponding un-
Surg Neural 1986;25:381-92
Figure 3. A 60-year-old man was referred with the diagnosis of a tranmatic subluxation at C4-5. (A) Lateral view of the cervical spine, showing degenerative anterolisthesis at C3-4 and C4-5 and degenerative retrolisthesis at CS-6. The disk spaces at CS-6 and Cb-7 are navroued. The disk spaces at C3-4 and C4-5, the levels of anterolisthesis, are normal. (B) Lateralpolytomogram of the facets, showing arthrotic changes at ~3-4 and C4-5 with spurs at the posterior aspects of the facets. The facet joint at 0-6, the level of retrolisfhesis, is normal.
Kim et al
cinate processes were hypertrophic viewed in the frontal projection.
and sclerotic
when
Ossification. Degenerative ossification in the anterior longitudinal ligament was misdiagnosed as a chip fracture in 5 cases. The ossification was seen in the lower cervical region (C4-5, C5-6, and Cb-7) in all cases. Associated degenerative lipping or flattening deformity was present at the anterior superior or anterior inferior corner of the vertebral bodies in all cases (Figure 6A and B).
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
385
A
Figure 4. A 67-year-old man was referred with the diagnosis of a traumatic retrolisthesis of C4-5. (A) Midline lateral polytomogram, showing degenerative retrolisthesis at C3-4 and C4-5. The disk spaces at C3-4, C4-5, and C5-6 are narrowed with end-plate irregularity and osteophytes. There is a mild degree of degenerative anterolisthesis at C2-3, the disk space of which is normal. (B) Lateral polytomogram at the facets showing the absence of arthrotic changes at the level of retrolisthesis, C3-4 and C4-5. There are arthrotic spurJ at the level of anterolisthesis, C2-3.
Preexisting Congenital Anomalies Ten patients (17.2%) with congenital malformations were misdiagnosed.
Block Vertebrae. Block vertebrae with subluxation was misdiagnosed as acute traumatic subluxation in eight cases. The patients' age and sex, the level of block vertebrae, the level, direction, and grade of subluxation, and the other associated features are listed in Table 2. In six patients with block vertebrae at the level from C3-4 to C6-7, anterolisthesis was noted at the adjacent higher level in five (Figure 7), and at a distant higher level in one. T h e r e was no facet arthrosis demonstrated radiographically in these cases, unlike in cases with spon-
dyloarthrotic anterolisthesis. In two patients with atlantooccipital fusion and block vertebrae at C2-3, atlantoaxial laxity was present in both (Figure 8A). In one of these, retrolisthesis was present at C4-5 and the disk space was maintained at this level (Figure 8A and B). This also was unlike the pattern seen in patients with spondylotic retrolisthesis.
Asymmetry of the Atlantoaxial Facets at the Base of the Odontoid. One case of anomalous development of the base of the odontoid with asymmetry of the atlantoaxial
386
Surg Neurol 1986 ;25: 381-92
Kim et al
Figure 5. (A) ~7-year-old man: (B) 50;year-rid woman, with degenerative flattening of the C-5 and C-6 bodies, mistaken for compression fractures. Note associated osteophytes, disk space narrowing, and ossification in the anterior longitudinal ligaments.
A
facets (Figure 9) was misinterpreted as being due to acute trauma.
Os Odontoideum. O n e case of os odontoideum was misinterpreted as an acute fracture. Physiologic Pseudosubluxation (pseudoanterolisthesis) in children and young adults was mistakenly interpreted as an acute subluxation in eight cases. The patients' age and sex and the level of pseudosubluxation are given in Table 3. The atlas-dens interval measured within 5 m m in flexion. The anterior subluxation of C-2 over C-3 did not exceed 4 m m in any case. The spinolaminar line was
normal. The anterior subluxation of C-3 over C-4 measured 2 a m .
Prominent Uncinate Processes Pseudo-offset of the posterior vertebral body line at C2-3 due to prominent uncinate processes of C-3 was seen in three instances. The uncinate processes may normally extend posterior to the posterior cortex of the vertebral body (Figures 10 and 11). Thus, when a line is drawn from the posterior aspect of the C-2 body to the p r o m i n e n t uncinate processes of C-3, a pseudo-offset of the posterior line of the vertebral body may result. Furthermore, because the uncinate processes are located at the lateral margins of the vertebral body, even a modest degree of rotation of the cervical spine may result in the uncinate processes projecting posterior to the posterior vertebral body line (Figure 12A). The spinolaminar line was normal in these cases (Figures 11 and 12A).
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
387
A
Mach Effect Pseudofracture of the odontoid produced by the Mach effect from overlapping shadows of the posterior arch of C-1 and the occiput was seen in two cases.
Normal Anatomic Variants N o r m a l anatomic variants were misinterpreted as acute cervical injuries in six cases: 1. N o r m a l wedging of the C-5 body in a 31-year-old woman. 2. N o r m a l backward displacement of the spinolaminar line at C-2 in a 61-year-old man. 3. Superior end-plate irregularity of the C-6 body due to a Schmorl's node in a 28-year-old man. 4. Slight increase of C6-7 disk space, misinterpreted as an extension injury in a 19-year-old woman. T h e r e was no abnormal widening of the anterior disk space in extension. 5. Pseudospread of the atlas was misdiagnosed as Jefferson's fracture in two patients. A 12-month-old child had lateral offsets on the two sides totaling 3 m m with an associated congenital vertical cleft in the anterior arch. Another case, a 16-year-old boy, had a lateral offset on both sides totaling 2 mm. A C T scan ruled out a Jefferson's fracture in these cases.
Figure 6. (A) 40-year-old woman; (B) 33-year-old man, with degenerative ossification in the anterior longitudinal ligament at the lower cervical spine, misinterpreted as an avulsion fracture. Note spondylotic spurs and flattening deformity of the adjacent anterior tvrner of the vertebral body.
Artifactual Lucent Line A superimposed artifactual lucent line simulated fracture over the C-4 body on the oblique view in one case and over the C-6 facets in the lateral view in another case.
Occult In four cases, the cause of the false positive interpretation could not be identified when the films of the cervical spine from outside our institution were reviewed.
Discussion The potential seriousness of missing an acute injury of the cervical spine creates a climate of high suspicion when cervical spine radiographs are viewed. In this situation, unfamiliarity with the various conditions that may mimic acute traumatic injury may lead to falsely positive diagnosis of an acute injury of the cervical spine.
388
Surg N e u r o l 1986;25:381-92
Kim et al
T a b l e 2. Cases of Block Vertebrae w i t h Subluxation Age
Level of block
Level of
Direction of
Grade of
vertebrae
subluxation
subluxation
subluxation
C5-6
C4-5
Anterolisthesis
l
M M
C4-5 C6-7
C3-4 C 5-6
Anterolisthesis Anterolisthesis
1 2
25 15 30 25
M F F M
C4-5 C3-4 C 5-6 A danto-occipital
C3-4 C2-3 C2-3 C 1-2
Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis
l 1 l 2
29
F
C2-3 Atlanto-occipital C2-3
C4-5 C 1-2
Retrolisthesis Anterolisthesis
2 2
Number
(yr)
Sex
l
36
F
2 3
13 15
4 5 6 7
8
Other features
Degenerative spurs at C5, C6, and C7 bodies Degenerative spur at C6 body, widened interspinous space at C5-6
Degenerative spur at C5 body
Abbreviations: F, female; M, male.
Figure 7. A 15-year-old boy with block vertebrae at C6-7 and foru,ard subluxation of C-5 on C-6, The subluxation was mistakenly thought to be due to acute trauma. Note a spur (arrow) from the anterior and superior aspect of C-6 body, buttressing the subluxed vertebra/ body above, The interspinous space between C-5 and C-6 is widened.
The consequence o f this misdiagnosis in our study included an average hospital stay of 3 days and the unnecessary application of traction devices. An awareness o f these false positive diagnostic pitfalls is important in evaluation o f suspected acute cervical spine injury. Preexisting degenerative disease was the most comm o n condition (39.6%) to be misinterpreted as an acute traumatic subluxation or fracture of the cervical spine. Degenerative subluxation accounted for 13 of 23 cases. In degenerative disease, motion is limited at the level o f the narrowed disk space. The facet joints above or below this level are subject to increased stress and develop arthrotic changes and stretching o f the ligaments and capsular structures. This leads to forward subluxation (anterolisthesis) of the vertebra in relation to the one below [18,21]. The disk space at the level o f anterolisthesis is usually preserved. Differential features from a traumatic subluxation are the absence o f fracture, the presence o f disk space narrowing above or below, facet arthrosis, and other degenerative changes such as spur formation o f the vertebral bodies and vacuum disk p h e n o m e n o n (Figures 1-3). Figure 8 (opposite, top). 25-year-old man with atlanto-occipital fusion and block vertebrae at C2-3. (A) Plain film of lateral cervical spine showing that atlantoaxial distance (between the arrowheads) is abnormally widened. There is retrolisthesis of C-4 on C-5. (B) Polytomogram showing a bony spur (arrow) from the posterior and superior aspect of C-5 body, buttressing the subluxed C-4 body. This is strong evidence against a traumatic origin of the subluxation.
Figure 9 (opposite, bottom). 23-year-old man. (A) Open mouth view. (B) Polytomogram of the atlantoaxial region, showing anomalous development of the base of the odontoid, misinterpreted as traumatic deformity of the odontoid. Note asymmetr~ of the atlantoaxial facets.
390
Surg Neurol 1986;25:381-92
Kim et al
Table 3. Cases woh Pseudosubluxation in Children and Young Adults Age Number 1
2 3 4 5 6 7 8
(yr)
Sex
3 mo
F
C 1-2
M M F F M M M
C2-3 C1-2 C1-2 C2-3 C2-3 C2-3 C2-3 C3-4
4 12 4 9 14 26 19
Level of pseudosubluxation
Abbreviations: F. female; M, male.
At the level of the disk space narrowing, backward subluxation (retrolisthesis) may develop in the upper vertebra in relation to the one below. This is due to the fact that as the height of the intervertebral disk diminishes, the upper vertebral body glides backward on the body below due to the posterior-inferior tilt of the facet joint surfaces [21]. Spondylotic retrolisthesis is most commonly seen in the midcervical region and is to be differentiated from traumatic extension injury. In spondylotic retrolisthesis, disk space narrowing, end-plate irregularity, sclerosis, and spur formation were always seen at the level of the slippage (Figure 4). In acute traumatic extension injury, the disk space is widened anteriorly in extension. An avulsion fragment and associated soft tissue swelling may be present. Retrolisthesis is also associated with hyperflexion tear-drop fracture. Fractures in the body and posterior elements, widening of the facet joint spaces, and prevertebral soft
Figure 10. Photograph of C-3 viewed from above. The uncinate processes
(arrows) project more posteriorly than the posterior aspect of the vertebral body in the midline.
Figure 11. Uncinate processes (arrow) of C-3 project posteriorly to the posterior vertebral bod~' h'ne (black line). This was mistakenly interpreted as offset of the posterior vertebral body line. Note normal spinolaminar line.
tissue swelling may be present in traumatic hyperflexion injury. Degenerative flattening of the vertebral body (platyspondylia) [20,21] was misinterpreted as a compression fracture in three cases. The features that may serve to differentiate from an acute traumatic compression fracture include the presence of osteophyte formation, disk space narrowing, and other degenerative changes such as vacuum phenomenon or ossification in the anterior longitudinal ligament (Figure 5). Uncovertebral joint degeneration may produce a horizontal lucent line on the lateral view of the cervical spine, which may be confused with a fracture [9,10,13]. In these cases, advanced degenerative changes such as osteophytes and disk space narrowing are always present. Hypertrophic and sclerotic uncinate processes may be identified at the corresponding level in the frontal projection. Furthermore, an isolated transverse fracture line in the vertebral body that is seen only on the lateral view is not known to occur. Degenerative ossification in the anterior longitudinal ligament may be confused with an avulsion fracture from
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
391
B
A
the anterior aspect of the vertebral body [ 13,21]. Spondylotic spurs or a flattening deformity of the anterior corner of the adjacent vertebral body are always present in degenerative ossification (Figure 6). The absence of soft tissue swelling or anterior widening of the disk space further serves to differentiate this from an avulsion injury. A preexisting congenital anomaly was the second most common condition (17.2%) that was confused with acute injuries. Congenital block vertebrae with subluxation accounted for 8 of 10 cases. Congenital block vertebrae are one of the most c o m m o n anomalies of the cervical spine [5]. In most cases, block vertebrae cause excessive stress at the level above or below, or both, although in some the added stress is at a more distant level. The manifestations of this stress are early spondylosis and subluxation (Figures 7 and 8) [5,18,19]. In contrast to the cases of degenerative spondyloarthrotic slippage, there was no facet arthrosis or intervertebral disk space narrowing demonstrated radiographically in this group. Spondylotic spurring was present, however, in cases with a high grade of subtuxation. In two of our cases, a subluxed vertebral body was buttressed by a spur from the vertebral body below (Figures 7 and 8B). This finding,
Figure 12. (A) One of the uncinate processes ¢black arrow~ projects posteriorly to the posterior t~ertebral body line with the cerl,ica/ spine rotated. This was mistakenly interpreted as offset of the posterior vertebral body line. Note the other uncinate process (white arrow) projects anteriorly to the posterior vertebral body line. The spinolaminar line is normal. (B) Midline lateral polytomogram showing normal posterior l,ertebral body line. Note a spur from the superior and posterior aspect of the C-4 bodv projecting posterior to the posterior vertebral body line.
if present, is strong evidence against an acute traumatic origin of the subluxation. Atlanto-occipital fusion is the most commonly recognized anomaly of the craniocervical junction [11]. Congenital fusion of C2~3 occurs in 7 0 % of patients with atlanto-occipital fusion [17]. In these patients, atlantoaxial laxity is likely to develop because greater demands are placed on this open joint when the joints above and below are fused [11]. The atlantoaxial joint space measured 6 - 7 m m in our two patients with atlanto-occipital fusion and block vertebrae at C2-3 (Figure 8A). Anomalous development o f the base of the odontoid [13,15,18] may offer difficulties in interpretation because the normal anatomic landmarks are obscured. An awareness of this rare condition is important if this anomaly is to be distinguished from an acute fracture. Recognition of asymmetry of atlantoaxial facets supports the diagnosis of congenital malformation (Figure 9). The os odontoideum is generally considered to be a developmental abnormality; however, there are opinions that it may be acquired as a result of an old ununited
392
Surg N e u r o l 1986;25:381-92
fracture of the dens. The os odontoideum should be easily differentiated from acute fractures of the dens. The os is rounded and does not match up with the body of the dens as is true in an odontoid fracture. Additionally, shortening of the sagittal diameter of the ring of the atlas or overdevelopment or absence of the anterior arch of the atlas may be present with os odontoideum [21]. Physiologic subluxation of the upper cervical spine in children and young adults was the third most common condition (13.8%) that was misdiagnosed as an acute traumatic subluxation. This condition has been well described in the literature [1,3,10,24]. The atlanto-odontold interval may measure up to 5 mm in a normal child up to age 15 and an occasional normal child is seen with a value even greater than this. Forward slip of up to 5 mm of C-2 on C-3 when the head or neck is flexed is a well-known normal finding in children up to the age of 10 years. Pseudosubluxation also occurs between C3 and C-4. Occasionally, pseudosubluxation is seen in young adults. Pseudo-offset of the posterior vertebral line at C2-3 may be seen stemming from prominent uncinate processes of C-3. This has not been previously described. The uncinate process may normally project posterior to the cortex of the vertebral body (Figures 10 and 11), and appear as a dense bone at the superior and posterior aspect of the body in the lateral view (Figures 11 and 12A). If a line is drawn from the posterior aspect of the C-2 body to the prominent uncinate process of C-3, the mistaken diagnosis of an offset posterior vertebral body line may result, especially when some rotation of the spine is present. It must be remembered that the uncinate processes are not components of the posterior vertebral body line. Occasionally a spur from the posterior and superior aspect of the C-3 and C-4 body may be seen projecting posterior to the posterior vertebral body line. Such a spur appears as a dense bone and should not be a component of the posterior vertebral body line (Fig. 12B). Other causes of falsely positive interpretation of cervical spine injury in our study include pseudofracture of the dens caused by Mach effect [4], normal wedge deformity of a vertebral body [ 15,21], normal backward displacement of the spinolaminar line at C-2 [14], and pseudospread of the atlas [8,23]. These have all been well described in the literature. References 1. Bailey DK. The normal cervical spine in infants and children. Radiology 1952;59:712-9.
Kim et al
2. Binet EF, Moro JJ, Marangola JP, Hodge CJ. Cervical spine tomography in trauma. Spine 1977;2:163-72. 3. Cattell HS, Filtzer DL. Pseudosubluxation and other normal variations in the cervical spine in children. A study of one hundred sixty children. J Bone Joint Surg 1965;47:1295-309. 4. Daffner RH. Pseudofracture of the dens: Math bands. AJR 1977;128:607-12. 5. de Graft R. Congenital block vertebrae C2-C3 in patients with cervical myelopathy. Acta Neurochir (Wien) 1982;6 l : 111-26. 6. Fielding JW. Os odontoideum: an acquired lesion. J Bone Joint Surg (Am) 1974;56(A):187-90. 7. Frieberger RH, Wilson PD, Nicholas JA. Acquired absence of the odontoid process. J Bone Joint Surg (Am) 1965;47(A): 1231-6. 8. GehweilerJA, Daffner RH, Roberts L. Malformations of the atlas vertebra simulating the Jefferson fracture. AJNR 1983 ;4:187-90. 9. Goldberg RP, Vine HS, Sacks BA, Ellison HP. The cervical split: a pseudofracture. Skeletal Radiol 1982;7:267-72. 10. Harrison RB, Keats TE, Winn HR, Riddervoid HO, Pope TL. Pseudosubluxation of the axis in young adults. J Can Assoc Radiol 1980;31:176-7. 11. Hensinger RN. Atlanto-occipital fusion. In: The Cervical Spine Research Society, ed. The cervical spine. Philadelphia: JB Lippincott, 1983:161-4. 12. Kassel EE, Cooper PW, Rubenstein JD. Radiology of spinal trauma: practical experience in a trauma unit. J Can Assoc Radiol 1983;34:189-203. 13. Katten KR. No trauma of the cervical spine. In: Katten KR, ed. "Trauma" and "no-trauma" of the cervical spine. Springfield, Ill: Charles C Thomas, 1975:242-75. 14. Katten KR. Backward "displacement" of the spinolaminar line at C-2: A normal variation. AJR 1977;129:289-90. 15. Keats TE. An atlas of normal roentgen variants that may simulate disease. Chicago: Year Book Medical Publishers, 1984:159-219. 16. Maravilla KR, Cooper PR, Sklar RH. The influence of thin-section tomography on the treatment of cervical spine injuries. Radiology 1978;127:131-9. 17. McRae DL. Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 1953;40:335-54. 18. McRae DL. The significance of abnormalities of the cervical spine. AJR 1960;84:3-25. 19. Nagib MG, Maxwell RE, Chou SN. Identification and management of the high risk patients with Klippel-Fell syndrome. J Neurosurgery 1984;61:523-30. 20. Payne EE, Spillane JD. The cervical spine. An anatomico-pathological study of 70 specimens (using a special technique) with particular reference to the problem of cervical spondylosis. Brain 1957;80:571-96. 21. Penning L. Obtaining and interpreting plain films in cervical spine injury. In: The Cervical Spine Research Society, ed. The cervical spine. Philadelphia: JB Lippincott, 1983:62-95. 22. Streitwiesen DR, Knopp R, Wales LR, Tonnemacher K. Accuracy of standard radiographic views in detecting cervical spine fractures. Ann Emerg Med 1983;12:538-42. 23. Suss RA, Zimmerman RD, Leeds NE. Pseudospread of the atlas: false sign of Jefferson fracture in young children. AJNR 1983; 4:183-6. 24. Townsend EH, Rowe ML. Mobility of the upper cervical spine in health and disease. Pediatrics 1952;10:567-72.
381
Pitfalls in Plain Film Diagnosis of Cervical Spine Injuries: False Positive Interpretation K w a n g S. K i r n , M . D . , L e e F. R o g e r s , M . D . , a n d V i c t o r R e g e n b o g e n ,
M.D.
Department of Radiology, Northwestern University Medical School, and Northwestern Memorial Hospital, Chicago, Illinois
Kim KS, Rogers LF, Regenbogen V. Pitfalls in plain film diagnosis of cervical spinal injuries: false positive interpretation. Surg Neurol 1986;25:381-92.
Of 412 patients who were referred and admitted with acute cervical spine injury, 58 (14%) were subsequently found to have no fracture or dislocation when evaluated at our institution. These patients had no abnormal neurological findings or severe persistent pain in the neck. Their referral was based on false positive interpretations of radiographs of the cervical spine. The radiographs in these cases are analyzed, and conditions that had led to misinterpretation are described. The radiographic differential features from true acute traumatic injury are discussed. KEY WORDS: Cervical spine; Acute trauma; Radiographic diagnosis; False positive interpretation
The accurate detection of fractures of the cervical spine is essential in the management of acutely traumatized patients. Pitfalls in the diagnosis o f plain film of cervical spine injuries that lead to false negative interpretation have been well documented [2,12,16,22]. Equally troubling; however, is the occurrence of false positive diagnosis of cervical spine injuries because of misinterpretation of cervical radiographs. O f cases referred to the Midwest Spinal Cord Injury Unit of the Northwestern Memorial Hospital, a regional referral center, 14% were found to have had a false positive interpretation o f the radiographs o f the cervical spine as the basis for their referral. These patients had no abnormal neurological findings or severe persistent pain in the neck. It is the purpose of this report to evaluate and characterize the radiographic features that may be misinterpreted as acute traumatic cervical spine injuries.
Address reprint requests to: K.S. Kim, M.D., Department of Radiology, Northwestern Memorial Hospital, Superior Street and Fairbanks Court, Chicago, Illinois 60611.
© 1986 by Elsevier Science Publishing Co., Inc.
Materials and Methods Four hundred twelve patients with acute cervical spine injuries, excluding those from gunshot wounds, were admitted to the Midwest Spinal Cord Injury Unit of the Northwestern Memorial Hospital between January 1982 and September 1984. The vast majority of these cases were referred from outlying community hospitals. Fiftyeight patients (14%) who were referred and admitted with the diagnosis o f fracture or dislocation, or both, based on outside cervical films, were subsequently found to have no fracture or dislocation when evaluated at our institution. These patients had no abnormal neurological findings or severe persistent pain in the neck. It is this group of patients that is the subject of this report. All patients were evaluated with our routine cervical sp!ne series (anteroposterior, lateral, both oblique and open mouth Views) as well as flexion and extension lateral views. Polytomography was obtained in most cases (87.9%) and computed tomography (CT) in some (8.6%). The medical records and outside radiographs were reviewed in all cases. Subluxation was graded arbitrarily from 1 to 4 based on 2-ram increments. Atlantoaxial subluxations were graded from 1 to 4 based on 2-ram increments beyond the 3-ram normal limit.
Results The following conditions have led to false positive diagnosis of acute traumatic fracture or dislocation of the cervical spine.
Preexisting Degenerative Disease Twenty-three patients (39.6%) with degenerative joint disease were wrongly thought to have suffered an acute traumatic injury.
Subluxation. Subluxation accounted for 13 of cases. The patients' age and sex, the direction and of subluxation, the level involved, and the level sociated disk space narrowing are listed in Table
these grade of as1.
0090-3019/86/$3.50
Table
1. Cases w i t h Degenerative Subluxation
Number
Age (yr)
Sex
Level
1 2 3 4 5 6 7 8 9 10 11 12
65 74 79 60 75 96 85 66 42 46 74 60
F F F F M M F F M F F M
13
73
M
C5-6 C4-5 C3-4 C6-7 C-7-T-I C4-5 C-7-T-I C5-6 C3-4 C5-6 C3-4 C3-4 C4-5 C5-6 C2-3 C3-4 C4-5
Direction of subluxation
Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis Retrolisthesis Retrolisthesis Retrolisthesis Retrolisthesis Anterolisthesis Anterolisthesis Retrolisthesis Anterolisthesis Retrolisthesis Retrolisthesis
Grade of subluxation
2 3 2 1 2 2 3 1 1 1 1 1 2
Disk space narrowing
C6-7 C5-6, C4-5, C5-6 C4-5, C5-6, C4-5, C5-6 C3-4 C5-6 C3-4, C5-6,
C6-7 C5-6 C5-6, C6-7 C6-7 C5-6, C6-7
C4-5, C5-6 C6-7
l
l 2 2
C3-4, C4-5, C5-6
Abbreviations: F, female; M, male. A
F i g u r e 1. A 74-year-old woman. (A) Lateral view of the cervical spine, showing degenerative anterolisthesis at C4-5, which was misinterpreted as a traumatic subluxation. There is a spur with a hooklike appearance (arrow) at the posterior aspect of the C5 facet. The disk spaces at the C5-6 and C6-7 levels are narrowed. (B) Lateral polytomogram of the facets showing the spur (arrow) from the posterior aspect of the C5 facet. The facet joint space is widened at the levd of anterolisthest~ but the joint surfaces remain parallel to each other.
B
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
383
A
In the cases with anterolisthesis, the forward slippage occurred from C2-3 to C - 7 - T - 1 levels. The amount of slippage varied from 1 to 6 mm. Every case o f anterolisthesis was associated with narrowing of the intervertebral disk spaces below or above the level of the slippage. The intervertebral disk space at the level of slippage was preserved in all cases (Figures 1-3). Various degrees of facet joint degeneration at the level of slippage were present in seven of nine cases. These degenerative changes were manifested by narrowing or widening of the joint space, sclerosis, spur formation, and a ribbonlike attenuation of the facets. The joint surfaces remained parallel to each other. These changes in the facet joints were best demonstrated by lateral polytomography (Figures 1-3). In the cases with retrolisthesis, the slippage occurred from C3-4 to C5-6 level. The degree of offset measured from 1 to 4 mm. The disk space was narrowed at the level of retrolisthesis in all cases. Degenerative changes such as end-plate irregularity, sclerosis, and spur formation were seen at the level of the retrolisthesis in all cases (Figures 3 and 4). In two cases, the presence of posterior osteophytes made evaluation of retrolisthesis difficult as it was not clear whether the posterior offset was a real finding,
Figure 2. An 85-year-old woman was referred with the diagnosis of a traumatic subluxation at C-7-T-1. (A) Midline lateral polytomogram, showing degeneratit~e anterolisthesis of C-7-T-1. The disk spaces above this level are narrowed, but the disk space at this level is maintained. (B) Lateral polytomogram of the facets showing thinning of the C-7 facet. The joint space at C-7-T-I is widened.
Platyspondylia. Degenerative flattening of the vertebral body (platyspondylia) was misdiagnosed as a compression fracture in three cases. The deformity was seen at either the C-5 or C-6 level, or both. Associated intervertebral disk space narrowing and degenerative spurring were present in all cases (Figure 5A and B). In one case, there was an associated vacuum p h e n o m e n o n in the disk spaces, and another case demonstrated ossification in the anterior longitudinal ligament at the C5-6 level. UncovertebraIJoint Degeneration. A horizontal lucent line seen in the lateral view over the vertebral body produced by uncovertebral joint degeneration was mistakenly diagnosed as a linear fracture in two cases. This lucency was seen over C-3 in one case and C-4 in the other case. Both cases demonstrated marked degenerative changes at multiple levels. The corresponding un-
Surg Neural 1986;25:381-92
Figure 3. A 60-year-old man was referred with the diagnosis of a tranmatic subluxation at C4-5. (A) Lateral view of the cervical spine, showing degenerative anterolisthesis at C3-4 and C4-5 and degenerative retrolisthesis at CS-6. The disk spaces at CS-6 and Cb-7 are navroued. The disk spaces at C3-4 and C4-5, the levels of anterolisthesis, are normal. (B) Lateralpolytomogram of the facets, showing arthrotic changes at ~3-4 and C4-5 with spurs at the posterior aspects of the facets. The facet joint at 0-6, the level of retrolisfhesis, is normal.
Kim et al
cinate processes were hypertrophic viewed in the frontal projection.
and sclerotic
when
Ossification. Degenerative ossification in the anterior longitudinal ligament was misdiagnosed as a chip fracture in 5 cases. The ossification was seen in the lower cervical region (C4-5, C5-6, and Cb-7) in all cases. Associated degenerative lipping or flattening deformity was present at the anterior superior or anterior inferior corner of the vertebral bodies in all cases (Figure 6A and B).
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
385
A
Figure 4. A 67-year-old man was referred with the diagnosis of a traumatic retrolisthesis of C4-5. (A) Midline lateral polytomogram, showing degenerative retrolisthesis at C3-4 and C4-5. The disk spaces at C3-4, C4-5, and C5-6 are narrowed with end-plate irregularity and osteophytes. There is a mild degree of degenerative anterolisthesis at C2-3, the disk space of which is normal. (B) Lateral polytomogram at the facets showing the absence of arthrotic changes at the level of retrolisthesis, C3-4 and C4-5. There are arthrotic spurJ at the level of anterolisthesis, C2-3.
Preexisting Congenital Anomalies Ten patients (17.2%) with congenital malformations were misdiagnosed.
Block Vertebrae. Block vertebrae with subluxation was misdiagnosed as acute traumatic subluxation in eight cases. The patients' age and sex, the level of block vertebrae, the level, direction, and grade of subluxation, and the other associated features are listed in Table 2. In six patients with block vertebrae at the level from C3-4 to C6-7, anterolisthesis was noted at the adjacent higher level in five (Figure 7), and at a distant higher level in one. T h e r e was no facet arthrosis demonstrated radiographically in these cases, unlike in cases with spon-
dyloarthrotic anterolisthesis. In two patients with atlantooccipital fusion and block vertebrae at C2-3, atlantoaxial laxity was present in both (Figure 8A). In one of these, retrolisthesis was present at C4-5 and the disk space was maintained at this level (Figure 8A and B). This also was unlike the pattern seen in patients with spondylotic retrolisthesis.
Asymmetry of the Atlantoaxial Facets at the Base of the Odontoid. One case of anomalous development of the base of the odontoid with asymmetry of the atlantoaxial
386
Surg Neurol 1986 ;25: 381-92
Kim et al
Figure 5. (A) ~7-year-old man: (B) 50;year-rid woman, with degenerative flattening of the C-5 and C-6 bodies, mistaken for compression fractures. Note associated osteophytes, disk space narrowing, and ossification in the anterior longitudinal ligaments.
A
facets (Figure 9) was misinterpreted as being due to acute trauma.
Os Odontoideum. O n e case of os odontoideum was misinterpreted as an acute fracture. Physiologic Pseudosubluxation (pseudoanterolisthesis) in children and young adults was mistakenly interpreted as an acute subluxation in eight cases. The patients' age and sex and the level of pseudosubluxation are given in Table 3. The atlas-dens interval measured within 5 m m in flexion. The anterior subluxation of C-2 over C-3 did not exceed 4 m m in any case. The spinolaminar line was
normal. The anterior subluxation of C-3 over C-4 measured 2 a m .
Prominent Uncinate Processes Pseudo-offset of the posterior vertebral body line at C2-3 due to prominent uncinate processes of C-3 was seen in three instances. The uncinate processes may normally extend posterior to the posterior cortex of the vertebral body (Figures 10 and 11). Thus, when a line is drawn from the posterior aspect of the C-2 body to the p r o m i n e n t uncinate processes of C-3, a pseudo-offset of the posterior line of the vertebral body may result. Furthermore, because the uncinate processes are located at the lateral margins of the vertebral body, even a modest degree of rotation of the cervical spine may result in the uncinate processes projecting posterior to the posterior vertebral body line (Figure 12A). The spinolaminar line was normal in these cases (Figures 11 and 12A).
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
387
A
Mach Effect Pseudofracture of the odontoid produced by the Mach effect from overlapping shadows of the posterior arch of C-1 and the occiput was seen in two cases.
Normal Anatomic Variants N o r m a l anatomic variants were misinterpreted as acute cervical injuries in six cases: 1. N o r m a l wedging of the C-5 body in a 31-year-old woman. 2. N o r m a l backward displacement of the spinolaminar line at C-2 in a 61-year-old man. 3. Superior end-plate irregularity of the C-6 body due to a Schmorl's node in a 28-year-old man. 4. Slight increase of C6-7 disk space, misinterpreted as an extension injury in a 19-year-old woman. T h e r e was no abnormal widening of the anterior disk space in extension. 5. Pseudospread of the atlas was misdiagnosed as Jefferson's fracture in two patients. A 12-month-old child had lateral offsets on the two sides totaling 3 m m with an associated congenital vertical cleft in the anterior arch. Another case, a 16-year-old boy, had a lateral offset on both sides totaling 2 mm. A C T scan ruled out a Jefferson's fracture in these cases.
Figure 6. (A) 40-year-old woman; (B) 33-year-old man, with degenerative ossification in the anterior longitudinal ligament at the lower cervical spine, misinterpreted as an avulsion fracture. Note spondylotic spurs and flattening deformity of the adjacent anterior tvrner of the vertebral body.
Artifactual Lucent Line A superimposed artifactual lucent line simulated fracture over the C-4 body on the oblique view in one case and over the C-6 facets in the lateral view in another case.
Occult In four cases, the cause of the false positive interpretation could not be identified when the films of the cervical spine from outside our institution were reviewed.
Discussion The potential seriousness of missing an acute injury of the cervical spine creates a climate of high suspicion when cervical spine radiographs are viewed. In this situation, unfamiliarity with the various conditions that may mimic acute traumatic injury may lead to falsely positive diagnosis of an acute injury of the cervical spine.
388
Surg N e u r o l 1986;25:381-92
Kim et al
T a b l e 2. Cases of Block Vertebrae w i t h Subluxation Age
Level of block
Level of
Direction of
Grade of
vertebrae
subluxation
subluxation
subluxation
C5-6
C4-5
Anterolisthesis
l
M M
C4-5 C6-7
C3-4 C 5-6
Anterolisthesis Anterolisthesis
1 2
25 15 30 25
M F F M
C4-5 C3-4 C 5-6 A danto-occipital
C3-4 C2-3 C2-3 C 1-2
Anterolisthesis Anterolisthesis Anterolisthesis Anterolisthesis
l 1 l 2
29
F
C2-3 Atlanto-occipital C2-3
C4-5 C 1-2
Retrolisthesis Anterolisthesis
2 2
Number
(yr)
Sex
l
36
F
2 3
13 15
4 5 6 7
8
Other features
Degenerative spurs at C5, C6, and C7 bodies Degenerative spur at C6 body, widened interspinous space at C5-6
Degenerative spur at C5 body
Abbreviations: F, female; M, male.
Figure 7. A 15-year-old boy with block vertebrae at C6-7 and foru,ard subluxation of C-5 on C-6, The subluxation was mistakenly thought to be due to acute trauma. Note a spur (arrow) from the anterior and superior aspect of C-6 body, buttressing the subluxed vertebra/ body above, The interspinous space between C-5 and C-6 is widened.
The consequence o f this misdiagnosis in our study included an average hospital stay of 3 days and the unnecessary application of traction devices. An awareness o f these false positive diagnostic pitfalls is important in evaluation o f suspected acute cervical spine injury. Preexisting degenerative disease was the most comm o n condition (39.6%) to be misinterpreted as an acute traumatic subluxation or fracture of the cervical spine. Degenerative subluxation accounted for 13 of 23 cases. In degenerative disease, motion is limited at the level o f the narrowed disk space. The facet joints above or below this level are subject to increased stress and develop arthrotic changes and stretching o f the ligaments and capsular structures. This leads to forward subluxation (anterolisthesis) of the vertebra in relation to the one below [18,21]. The disk space at the level o f anterolisthesis is usually preserved. Differential features from a traumatic subluxation are the absence o f fracture, the presence o f disk space narrowing above or below, facet arthrosis, and other degenerative changes such as spur formation o f the vertebral bodies and vacuum disk p h e n o m e n o n (Figures 1-3). Figure 8 (opposite, top). 25-year-old man with atlanto-occipital fusion and block vertebrae at C2-3. (A) Plain film of lateral cervical spine showing that atlantoaxial distance (between the arrowheads) is abnormally widened. There is retrolisthesis of C-4 on C-5. (B) Polytomogram showing a bony spur (arrow) from the posterior and superior aspect of C-5 body, buttressing the subluxed C-4 body. This is strong evidence against a traumatic origin of the subluxation.
Figure 9 (opposite, bottom). 23-year-old man. (A) Open mouth view. (B) Polytomogram of the atlantoaxial region, showing anomalous development of the base of the odontoid, misinterpreted as traumatic deformity of the odontoid. Note asymmetr~ of the atlantoaxial facets.
390
Surg Neurol 1986;25:381-92
Kim et al
Table 3. Cases woh Pseudosubluxation in Children and Young Adults Age Number 1
2 3 4 5 6 7 8
(yr)
Sex
3 mo
F
C 1-2
M M F F M M M
C2-3 C1-2 C1-2 C2-3 C2-3 C2-3 C2-3 C3-4
4 12 4 9 14 26 19
Level of pseudosubluxation
Abbreviations: F. female; M, male.
At the level of the disk space narrowing, backward subluxation (retrolisthesis) may develop in the upper vertebra in relation to the one below. This is due to the fact that as the height of the intervertebral disk diminishes, the upper vertebral body glides backward on the body below due to the posterior-inferior tilt of the facet joint surfaces [21]. Spondylotic retrolisthesis is most commonly seen in the midcervical region and is to be differentiated from traumatic extension injury. In spondylotic retrolisthesis, disk space narrowing, end-plate irregularity, sclerosis, and spur formation were always seen at the level of the slippage (Figure 4). In acute traumatic extension injury, the disk space is widened anteriorly in extension. An avulsion fragment and associated soft tissue swelling may be present. Retrolisthesis is also associated with hyperflexion tear-drop fracture. Fractures in the body and posterior elements, widening of the facet joint spaces, and prevertebral soft
Figure 10. Photograph of C-3 viewed from above. The uncinate processes
(arrows) project more posteriorly than the posterior aspect of the vertebral body in the midline.
Figure 11. Uncinate processes (arrow) of C-3 project posteriorly to the posterior vertebral bod~' h'ne (black line). This was mistakenly interpreted as offset of the posterior vertebral body line. Note normal spinolaminar line.
tissue swelling may be present in traumatic hyperflexion injury. Degenerative flattening of the vertebral body (platyspondylia) [20,21] was misinterpreted as a compression fracture in three cases. The features that may serve to differentiate from an acute traumatic compression fracture include the presence of osteophyte formation, disk space narrowing, and other degenerative changes such as vacuum phenomenon or ossification in the anterior longitudinal ligament (Figure 5). Uncovertebral joint degeneration may produce a horizontal lucent line on the lateral view of the cervical spine, which may be confused with a fracture [9,10,13]. In these cases, advanced degenerative changes such as osteophytes and disk space narrowing are always present. Hypertrophic and sclerotic uncinate processes may be identified at the corresponding level in the frontal projection. Furthermore, an isolated transverse fracture line in the vertebral body that is seen only on the lateral view is not known to occur. Degenerative ossification in the anterior longitudinal ligament may be confused with an avulsion fracture from
Cervical Spine Injuries
Surg Neurol 1986;25:381-92
391
B
A
the anterior aspect of the vertebral body [ 13,21]. Spondylotic spurs or a flattening deformity of the anterior corner of the adjacent vertebral body are always present in degenerative ossification (Figure 6). The absence of soft tissue swelling or anterior widening of the disk space further serves to differentiate this from an avulsion injury. A preexisting congenital anomaly was the second most common condition (17.2%) that was confused with acute injuries. Congenital block vertebrae with subluxation accounted for 8 of 10 cases. Congenital block vertebrae are one of the most c o m m o n anomalies of the cervical spine [5]. In most cases, block vertebrae cause excessive stress at the level above or below, or both, although in some the added stress is at a more distant level. The manifestations of this stress are early spondylosis and subluxation (Figures 7 and 8) [5,18,19]. In contrast to the cases of degenerative spondyloarthrotic slippage, there was no facet arthrosis or intervertebral disk space narrowing demonstrated radiographically in this group. Spondylotic spurring was present, however, in cases with a high grade of subtuxation. In two of our cases, a subluxed vertebral body was buttressed by a spur from the vertebral body below (Figures 7 and 8B). This finding,
Figure 12. (A) One of the uncinate processes ¢black arrow~ projects posteriorly to the posterior t~ertebral body line with the cerl,ica/ spine rotated. This was mistakenly interpreted as offset of the posterior vertebral body line. Note the other uncinate process (white arrow) projects anteriorly to the posterior vertebral body line. The spinolaminar line is normal. (B) Midline lateral polytomogram showing normal posterior l,ertebral body line. Note a spur from the superior and posterior aspect of the C-4 bodv projecting posterior to the posterior vertebral body line.
if present, is strong evidence against an acute traumatic origin of the subluxation. Atlanto-occipital fusion is the most commonly recognized anomaly of the craniocervical junction [11]. Congenital fusion of C2~3 occurs in 7 0 % of patients with atlanto-occipital fusion [17]. In these patients, atlantoaxial laxity is likely to develop because greater demands are placed on this open joint when the joints above and below are fused [11]. The atlantoaxial joint space measured 6 - 7 m m in our two patients with atlanto-occipital fusion and block vertebrae at C2-3 (Figure 8A). Anomalous development o f the base of the odontoid [13,15,18] may offer difficulties in interpretation because the normal anatomic landmarks are obscured. An awareness of this rare condition is important if this anomaly is to be distinguished from an acute fracture. Recognition of asymmetry of atlantoaxial facets supports the diagnosis of congenital malformation (Figure 9). The os odontoideum is generally considered to be a developmental abnormality; however, there are opinions that it may be acquired as a result of an old ununited
392
Surg N e u r o l 1986;25:381-92
fracture of the dens. The os odontoideum should be easily differentiated from acute fractures of the dens. The os is rounded and does not match up with the body of the dens as is true in an odontoid fracture. Additionally, shortening of the sagittal diameter of the ring of the atlas or overdevelopment or absence of the anterior arch of the atlas may be present with os odontoideum [21]. Physiologic subluxation of the upper cervical spine in children and young adults was the third most common condition (13.8%) that was misdiagnosed as an acute traumatic subluxation. This condition has been well described in the literature [1,3,10,24]. The atlanto-odontold interval may measure up to 5 mm in a normal child up to age 15 and an occasional normal child is seen with a value even greater than this. Forward slip of up to 5 mm of C-2 on C-3 when the head or neck is flexed is a well-known normal finding in children up to the age of 10 years. Pseudosubluxation also occurs between C3 and C-4. Occasionally, pseudosubluxation is seen in young adults. Pseudo-offset of the posterior vertebral line at C2-3 may be seen stemming from prominent uncinate processes of C-3. This has not been previously described. The uncinate process may normally project posterior to the cortex of the vertebral body (Figures 10 and 11), and appear as a dense bone at the superior and posterior aspect of the body in the lateral view (Figures 11 and 12A). If a line is drawn from the posterior aspect of the C-2 body to the prominent uncinate process of C-3, the mistaken diagnosis of an offset posterior vertebral body line may result, especially when some rotation of the spine is present. It must be remembered that the uncinate processes are not components of the posterior vertebral body line. Occasionally a spur from the posterior and superior aspect of the C-3 and C-4 body may be seen projecting posterior to the posterior vertebral body line. Such a spur appears as a dense bone and should not be a component of the posterior vertebral body line (Fig. 12B). Other causes of falsely positive interpretation of cervical spine injury in our study include pseudofracture of the dens caused by Mach effect [4], normal wedge deformity of a vertebral body [ 15,21], normal backward displacement of the spinolaminar line at C-2 [14], and pseudospread of the atlas [8,23]. These have all been well described in the literature. References 1. Bailey DK. The normal cervical spine in infants and children. Radiology 1952;59:712-9.
Kim et al
2. Binet EF, Moro JJ, Marangola JP, Hodge CJ. Cervical spine tomography in trauma. Spine 1977;2:163-72. 3. Cattell HS, Filtzer DL. Pseudosubluxation and other normal variations in the cervical spine in children. A study of one hundred sixty children. J Bone Joint Surg 1965;47:1295-309. 4. Daffner RH. Pseudofracture of the dens: Math bands. AJR 1977;128:607-12. 5. de Graft R. Congenital block vertebrae C2-C3 in patients with cervical myelopathy. Acta Neurochir (Wien) 1982;6 l : 111-26. 6. Fielding JW. Os odontoideum: an acquired lesion. J Bone Joint Surg (Am) 1974;56(A):187-90. 7. Frieberger RH, Wilson PD, Nicholas JA. Acquired absence of the odontoid process. J Bone Joint Surg (Am) 1965;47(A): 1231-6. 8. GehweilerJA, Daffner RH, Roberts L. Malformations of the atlas vertebra simulating the Jefferson fracture. AJNR 1983 ;4:187-90. 9. Goldberg RP, Vine HS, Sacks BA, Ellison HP. The cervical split: a pseudofracture. Skeletal Radiol 1982;7:267-72. 10. Harrison RB, Keats TE, Winn HR, Riddervoid HO, Pope TL. Pseudosubluxation of the axis in young adults. J Can Assoc Radiol 1980;31:176-7. 11. Hensinger RN. Atlanto-occipital fusion. In: The Cervical Spine Research Society, ed. The cervical spine. Philadelphia: JB Lippincott, 1983:161-4. 12. Kassel EE, Cooper PW, Rubenstein JD. Radiology of spinal trauma: practical experience in a trauma unit. J Can Assoc Radiol 1983;34:189-203. 13. Katten KR. No trauma of the cervical spine. In: Katten KR, ed. "Trauma" and "no-trauma" of the cervical spine. Springfield, Ill: Charles C Thomas, 1975:242-75. 14. Katten KR. Backward "displacement" of the spinolaminar line at C-2: A normal variation. AJR 1977;129:289-90. 15. Keats TE. An atlas of normal roentgen variants that may simulate disease. Chicago: Year Book Medical Publishers, 1984:159-219. 16. Maravilla KR, Cooper PR, Sklar RH. The influence of thin-section tomography on the treatment of cervical spine injuries. Radiology 1978;127:131-9. 17. McRae DL. Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol 1953;40:335-54. 18. McRae DL. The significance of abnormalities of the cervical spine. AJR 1960;84:3-25. 19. Nagib MG, Maxwell RE, Chou SN. Identification and management of the high risk patients with Klippel-Fell syndrome. J Neurosurgery 1984;61:523-30. 20. Payne EE, Spillane JD. The cervical spine. An anatomico-pathological study of 70 specimens (using a special technique) with particular reference to the problem of cervical spondylosis. Brain 1957;80:571-96. 21. Penning L. Obtaining and interpreting plain films in cervical spine injury. In: The Cervical Spine Research Society, ed. The cervical spine. Philadelphia: JB Lippincott, 1983:62-95. 22. Streitwiesen DR, Knopp R, Wales LR, Tonnemacher K. Accuracy of standard radiographic views in detecting cervical spine fractures. Ann Emerg Med 1983;12:538-42. 23. Suss RA, Zimmerman RD, Leeds NE. Pseudospread of the atlas: false sign of Jefferson fracture in young children. AJNR 1983; 4:183-6. 24. Townsend EH, Rowe ML. Mobility of the upper cervical spine in health and disease. Pediatrics 1952;10:567-72.