Imaging in the diagnosis of musculoskeletal infections in children

Imaging in the Diagnosis of Musculoskeletal Infections in Children Gerald A. Mandell, MD

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nfection of the musculoskeletal system in children can involve the osseous system (osteomyelitis), the contiguous soft tissues (synovitis, arthritis, and cellulitis), or both. The conventional radiograph, still the first imaging evaluation, is important in screening for musculoskeletal infection by excluding other pathologic conditions. Bone scintigraphy is very sensitive for early localization of the hyperemia and bone resorption of the infectious process, which predates changes visible on plain radiographs by at least 10 days. In the nuclear armamentarium, specificity may be heightened with gallium-67 citrate (gallium) and tagged white blood cell studies. The newer imaging modalities (computed tomography [CT], magnetic resonance imaging [MRI], and ultrasound [US]) are usually considered for further anatomic detail following the localization of the osseous or soft-tissue abnormality. The types of imaging studies used vary according to the patient's age (infantile, juvenile, and adult types), clinical presentation (acute, subacute, and chronic), and the route of infection (hematogenous and nonhematogenous). infantile osteomyelitis occurs between birth and 1 year of age, the juvenile form between 1 year and the closure of the physes, and the adult type after the closure of the physes. In general, infantile and early juvenile forms of osteomyelitis are seen with more systemic signs (high fever and elevated white blood cell count). The more indolent, subacute forms of bone infection more commonly affect older juveniles (i.e., latter half of first decade and first half of second decade). Multifocal osteomyelitis of infancy (the first few weeks or months of life) may result in significant bone and joint destruction if the process is unrecognized or inadequately

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Gerald A. Mandett, MD, is chief of nuclear medicine in the Department of Medical Imaging at the Alfred I. duPont Institute, in Wilmington, Delaware. Curr Probl Pediatr 1996;26:218-37. Copyright 9 1996 by Mosby-Year Book, Inc. 0045-9380/96/$6.00 + .10 5 3 / 1 / 7 5 9 8 3

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treated. The chronic recurrent multifocal osteomyelitis (CRMO), seen in persons from about 5 to 15 years of age, is very indolent with very little systemic manifestations (absence of fever and moderately elevated sedimentation rate) and often localized symptoms of pain and minimal swelling. The classification of bone infection can also be geographic. In h e m a t o g e n o u s osteomyelitis, the metaphyses of the long bones are still the most commonly affected sites in all age groups. Other less-common locations are also appendicular and frequently affect different age groups (i.e., epiphyseal and diaphyseal [infantile and latter half of first decade]). The axial skeleton is affected during infancy, and preadolescence with diskitis (an indolent infection of the intervertebral disk space) and with infection of the bony pelvis (metaphyseal-equivalent osteomyelitis) in preadolescence and adolescence. In general, the most common infecting organisms of bone are Staphylococcus aureus followed by group B ~-hemolytic streptococcus, which is most frequent in infancy. Nonhematogenous osteomyelitis in children occurs as a result of penetrating trauma (nailthrough-the-sneaker Pseudomonas infection), complicated surgical procedure, and contiguous soft-tissue infection (skin, paranasal sinus, pleura). After the development of antibiotic agents, there was a dramatic decrease in the overall incidence of osteomyelitis. Now, the subacute variety of hematogenous osteomyelitis (10% to 15% of all new cases) 1 and CRMO are contributing to an increased proportion of new cases. The changing patterns of osteomyelitis presumably result from the frequent and often inadequate use of antibiotics. Early diagnosis and subsequent appropriate treatment of musculoskeletal infection are imperative to maximize the chances of favorable long-term results, thus preventing leg-length discrepancies, angular deformities, and ankylosis. Before the introduction of antibacterial drugs, 25% of children with acute hematogenous osteomyelitis died as a result of the associated septicemiaJ

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D ( Fig. 1. An 11 -year-old with acute hematogenous osteomyelitis. A, Radiograph shows normal anteroposterior projection of right knee. B, Bone scan shows anterior angiographic images demonstrating increased activity in the right femur. C, Anterior soft-tissue image of knees with increased uptake in right distal femoral metaphysis. D, Anterior delayed image of knees with increased uptake in right distal femoral metaphysis especially concentrated in the lateral metaphysis.

Hematogenous Osteomyelitis

Pathophysiology A child with suspicion of acute bone infection usually has fever, pain, and an elevated white blood cell count and sedimentation rate. More than 75% of acute hematogenous osteomyelitis primarily affects the metaphyses of the long bones with the faster growing and largest metaphyses (wrist, humerus, and knee affected first) (Fig. 1). Flat bones (e.g., ilium, vertebra, and calcaneus) are affected 25% of the time. Bloodborne organisms flourish in the large venous sinusoids (terminal capillary loops) within the intramedullary portion of the metaphysis. Transphyseal vessels allow spread into the epiphyses and joints, usually in patients

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less than 18 months of age. The inflammatory response, exudate, may cause increased intraosseous pressure with resultant stasis of blood flow and thrombosis and, ultimately, bone necrosis and bone resorption. The purulent material may perforate through the cortex and displace the adjacent soft tissues. Subacute osteomyelitis is a relatively benign indolent (about 2 weeks of symptoms) localized, pyogenic process (Brodie's abscess) (Fig. 2). The afebrile child is initially seen with pain or limp, an elevated sedimentation rate, and usually a normal white blood cell count. Some neutrophils and other inflammatory cells appear in the aspirate or biopsy specimen. S. a u r e u s is isolated usually less than 50% of the time. The intravenous administration of a high-dose of appropriate antimicro-

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B Fig. 2. A 4-year-old with imaging of subacute osteomyelitis. A, Radiograph shows anteroposterior view of the pelvis with suggestion of some rarefaction along greater trochanter of right proximal femur (arrow). 13, Bone scan, pin-hole high-resolution image demonstrating increased uptake in right greater trochanter (arrow). C, TransaxiatCT of proximal femoral demonstrating circumscribed lyric lesion in greater trachanter of right proximal femur (arrow).

bial therapy is usually recommended, followed by an oral course of antibiotics. Early diagnosis and proper antimicrobial treatment prevents chronic osteomyelitis (sequestrum/involucrum formation). A sequestrum is a necrotic piece of bone within the inflammatory process, and the involucrum involves the periosteal cloaking of the dead bone. The presence of necrotic tissue may lead to draining sinuses. Chronic osteomyelitis is a continuous infection of a lowgrade or recurrent type (Fig. 3). The biopsy specimen in chronic osteomyelitis is usually absent of microorganisms and predominantly demonstrates lymphocytes and plasma cells rather than polymorphonuclear cells. There is a variable amount of necrotic tissue that protects organisms from antibiotics. Bacteria may remain indolent for a long time, with reactivation of the disease years after the acute episode.

Conventional Radiography Plain radiographs should always be the first step in the imaging evaluation for osteomyelitis to exclude other pathologic conditions rather than to specifically diagnose the disease. High-quality radiographs enable the detection of the earliest sign of acute hematogenous osteomyelitis, deep s o , t i s s u e swelling with the displacement of the adjacent musculature on the first to third day of the illness. 2 During the the next 2 days, the inflammatory process may expand to cause swelling of

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the adjacent musculature. Bone destruction and periosteal reaction may not become evident for 10 to 21 days after the onset of the disease. 3 Lysis of bone cannot be appreciated until the lesion is 1.0 to 1.5 cm or until 30% to 50% of the bone matrix has been destroyed. Negative conventional radiographs are not reliable as the sole imaging procedure in children suspected of having osseous infection with less than 10 days of symptoms (Fig. 1, A). Cellulitis (infection in the soft tissues) may be clinically and radiographically indistinguishable from acute hematogenous osteomyelitis. The differentiation relies on bone scintigraphy and sometimes other imaging. Subacute osteomyelitis is most frequently seen in the metaphysis of the tibia or femur within a few centimeters of the physis. The diaphysis and epiphysis are alternate sites. Subacute osteomyelitis has radiographic findings most commonly represented by a well-defined area of lysis, usually circumscribed by a thin rim of sclerosis. Organization in the intramedullary space of a cystic cavity represents the intraosseous abscess (Brodie's abscess). Periosteal reaction is minimal or absent. Sometimes the margin of the lesion is less well defined and extends into the diaphysis and epiphysis, raising a suspicion for an aggressive bone tumor. Local soft-tissue swelling or mass may not be identified. In children, the focus of infection may be so small (a few millimeters) that detection on plain radiography is not possible (Fig. 2, A). Bone

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B Fig. 3. An 11-year-old with chronic osteomyelitis in a violated bone. A, Bone scan, anterior delayed image of knees demonstrating areas of increased uptake and areas of photopenia or decreased uptake (arrows) in the distal left femur. Indium-Ill tagged white blood cell study. 13, Twenty-four-hour delayed image of left knee demonstrating areas uptake of the radiotracer in regions (arrows) not accumulating the bone agent on lhe bone scan.

scintigraphy with localization of a focus of increased bone turnover and subsequent CT demonstration are necessary (Fig. 2, B and C). Chronic osteomyelitis, a continuous infection of a lowgrade or a recurrent type, is characterized by predominantly bony sclerosis, periosteal new bone formation and the presence of a few sequestra and/or draining sinuses. It is uncommon in children without some type of instrumentation (rods, fixation devices). Considerable diaphyseal new bone formation (Garr6's sclerosing osteomyelitis) can mimic an osteoid osteoma, Ewing sarcoma, and so on.

Bone Scintigrophy Bone scintigraphy lends itself to the detection of acute and subacute osteomyelitis because the bone-seeking radiopharmaceuticals avidly concentrate in the local area of hyperemia and the initial bone resorption induced by the infectious process. Bone repair also contributes to the activity of the bone scan in subacute and chronic infections. The multiphase bone scan (two or three phases) is the imaging modality of choice in cases of suspected acute osteomyelitis, becoming positive within 24 to 48 hours after the onset of symptoms4; this scan

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has been invaluable in differentiating cellulitis from osteomyelitis in the proper clinical setting. 5 The threephase bone scan consists of a flow, or angiographic, phase (1- to 5-second frames for 1 minute after the injection of the bolus of bone agent--i.e., technetium99m methylene diphosphonate), a blood-pool, or softtissue, phase (static high-count images within 5 to 15 minutes after the flow phase), and a delayed phase (static images 2 to 3 hours after injection) (Fig. 1, B, C, and D). Recently, some authors have proposed adding a 24hour image, a fourth phase, because the amount of activity in the lesion theoretically continues to increase with time. The multiphase bone scan (two or three phases) has been very sensitive and specific in differentiating cellulitis from osteomyelitis in the scenario of normal radiographs and the proper clinical setting (Fig. 4). 5 Classically, with cellulitis or soft-tissue infection, diffuse or regional increased uptake occurs in the first two phases, but uptake disappears or lessens on the delayed images of the bone scan? The classical scintigram demonstrates discrete increased uptake on the two early phases (angiographic and blood-pool) and increased uptake localizing to the infected focus of bone on the delayed image. The

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in the axial s k e l e t o n (vertebrae, ribs, and temperomandibular joints). Some reportings indicate that the radionuclide accumulation in neonates, as well as in older children, may be either reduced ("cold") or normal (false-negative) (Fig. 5). The cold lesion usually occurs early in the course of acute osteomyelitis and usually represents relative ischemia produced by the increased pressure of the intraosseous and subperiosteal purulent material. A cold scan accompanied by clinical signs suggestive of infection means osteomyelitis until proved otherwise. The predictive value of a "hot" scan has been reported as 82% and of a cold scan as 100%. 7 The normal appearance of the bone scan in osteomyelitis may represent the transition phase from the cold to hot phases, v,g If the patient has been receiving antibiotic treatment for several days before referral for the bone scan, false-negative scans may also occur. When bone has not been affected by other pathologic conditions (violated) such as spinal fusion, the bone scan has a sensitivity and specificity of approximately 9 0 % . 9 In violated bone, the bone scan is still sensitive (93%) but not specific (34%).1~ The increased uptake may represent bone repair as well as superimposed osteomyelitis (Fig. 3, A). The specificity is again improved with gallium or labeled leukocyte scintigrapby. Although the bone scan readily accumulates the bone tracer in acute disease, it cannot be used to evaluate the response to antimicrobial treatment because the bone scan remains positive for months after clinical resolution of the disease. Fig. 4. A 2-year-old with cellulitis (soft-tissue infection). A, Bone scan, anterior soft-tissue imaging of the forearms with diffuse increased uptake in right elbow and proximal forearm. 13, Normal delayed anterior view of the forearms.

multifocality of infection of the skeleton in infants and preadolescent/adolescent children often necessitates the imaging of the whole body in both blood-pool and delayed phases of the bone scan. Specialized techniques of the bone scintigraphy include pin-hole collimation (high-resolution magnification views) and single-photon emission computed tomography (SPECT) for better separation of the metaphyseal/physeal/epiphyseal complexes of long bones, differentiation of pathologic processes in the hip area, and definition of active processes affecting the small bones of the hands and feet, pin-hole collimation is used. produces tomograms with sagittal, coronal, and transaxial slicing (similar to MRI) for the detection of subtle foci of the abnormal uptake

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Gallium-67 Citrate (Gallium) Imaging Gallium has chemical and biological properties similar to iron. Gallium may be transferred by plasma proteins (transferrin and lactoferrin) to the membranes of both bacteria and neutrophils and be incorporated as proteins in intracellular structures. Gallium, however, is not very specific for infection. Gallium's fixation to polymorphonuclear leukocytes can give false-positive results in inflammatory processes such as rheumatoid arthritis. Neoplastic uptake (lymphoma, sarcoma, etc.) results because of gallium's affinity for the membranes and the intracellular lysosomes of some tumor cells. Early scanning with gallium (3 to 4 hours after intravenous injection) has an accuracy of 91% in the detection of arthritis and osteomyelitis in children.~~ Gallium, even in the presence of relative ischemia, is a more sensitive indicator of infection than bone scintigraphy. However, this radiopharmaceutical was originally pro-

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D C Fig. 5. An 8-year-old with acute hematogenous osteomyelitis. A, Radiograph, unremarkable anteroposterior view of the left knee. B, Bone scan, anterior soft-tissue images of the knees with question of mild increased accumulation of radiotracer in left distal femoral metaphysis (arrow). C, Unremarkable anterior delayed images of knees. 13, Tc-99m white blood cell study, anterior image of knees with definite increased uptake in distal left femoral diaphysis and metaphysis.

posed as a bone scanning agent, and it shows increased uptake in areas of increased bone remodeling. Combined gallium and bone scanning increases the accuracy of the scintigraphically derived diagnosis of o s t e o m y e l i t i s in bones c o m p l i c a t e d by surgery, pseudarthrosis, or neuropathic change. 1~,~2Gallium uptake exceeding that seen on bone scan and incongruence of spatial distribution of gallium and bone uptake are considered reliable indicators of osteomyelitis. 13

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Gallium scintigraphy is relegated to usage in certain difficult cases because of its higher radiation burden than that of routine bone scintigraphy.

Tagged White Blood Cell Imaging More specificity to the detection of infection in bone has been added by the introduction of indium- 111 and technetium-99m tagged white blood cell studies. These studies are usually reserved for those situations where

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Fig. 6. A 10-year-old with metaphyseal equivalent osteomyelitis.A, Bone scan, posterior soft-tissue image of pelvis with increased uptake in the right sacroiliac joint (arrow). B, Delayed posterior image of pelvis with increased accumulation of radiotracer in right sacroiliac joint (arrow). C, CT, transaxial scan of prone pelvis with erosive changes (arrow) along sacral margin of right sacroiliac joint with associated widening of the joint space.

bone scan findings are equivocal or normal and osseous infection is still a likely consideration. Labeling of white blood cells usually requires at least a volume of 20 ml of blood. Extensive and careful separation of the white blood cells as well as special attention to proper identification of blood samples (quality control) are necessary. The labeling procedure usually takes about 2 hours and requires skill to ensure that the cells are not damaged. The labeled polymorphonuclear leukocyte is the main responder to acute infection and can localize infection when suspected osteomyelitis is superimposed on processes that cause increased bone remodelingJ 4 The white blood cells are injected as a mixture of predominantly labeled polymorphonuclear leukocytes and other labeled blood components (lymphocytes, monocytes, red blood cells, platelets, .and plasma proteins). There is some controversy over the sensitivity of these

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agents to chronic infection, which consist mainly of m a c r o p h a g e s , l y m p h o c y t e s , and p l a s m a cells. Schauwecker et al. ~5 reported a 60% sensitivity with indium- 111 imaging in chronic osteomyelitis. The sensitivity of chronic osteomyelitis varied with location, 94% for peripheral bones, 80% for middle bones, and 53% for the central skeleton. In acute osteomyelitis, the sensitivity was 90% to 95%, regardless of location of the bone in the body (Fig. 3). The use of t e c h n e t i u m - 9 9 m h e x a m e t h y l p r o pyleneamine oxime (HMPAO)-labeled leukocytes has been popularized in children (Fig. 5, D). The radiation burden of technetium-99m (lower energy and shorter half-life) is significantly less than that of indium-111 tagged white cells. Better resolution of the infectious process with technetium-99m tagged white cells is permitted by higher counts (approximately 40 times more

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Fig. 7. A 10-year-old with diskitis. A, MRI, a T~-weighted image of the lumbar spine region with decreased signal and diminution of intervening disk space L2-3. Soft-tissue mass protruding from anterior-inferior margin of L2 and anterior-superior margin of L3 (arrow). B, T2-weighted image with markedly decreased signal of the involved disk space (arrow) and increased signal of the adjoining vertebral bodies.

than indium-111), and thus faster imaging time (less patient motion). Earlier image acquisition (within 4 hours) permits earlier diagnosis. Imaging with indium111 tagged white cells usually requires at least 24 hours. Preliminary results with technetium-99m HMPAO cells have been encouraging, although some false-negative results have been reported, l-s.~6The presence of extensive marrow uptake in children may interfere with interpretation. Additional experience will be necessary to determine the role of these agents in imaging of bone infection.

Cross-sectional (Multiplanar) Imaging CT and MRI are usually considered when there is an indication of localized disease on physical examination or screening imaging modality such as the bone scan. Neither CT nor MRI is recommended as the first choice in diagnostic imaging because both tests are expensive, may require sedation in young children, and cannot scan the entire body. MRI should be used only when it might provide information unavailable from less-expensive imaging methods and when the results might significantly affect management. Both CT and MRI can show the changes of infection earlier than plain radiography. These imaging modalities are particularly useful in spinal and pelvic infections (Figs. 2, C, and 6, C). CT is very reliable in detecting cortical destruction, periosteal reaction, and soft-tissue extension. ~7 In diagnosing infection and its soft-tissue component, most radiologists recommend that the CT examination be performed with and without iodinated contrast. CT is superior to MRI for the detection of sequestra and the presence of intraosseous gas, an infrequent but reliable sign of osteomyelitis.

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MRI is particularly useful in detailing the soft-tissue and osseous components of infection involving the axial skeleton (spine and pelvis) or for chronic bone infection (Fig. 7). ~s MRI with its sagittal, coronal, and transaxial orientations is very sensitive (97%) and specific (92%) in the diagnosing of acute hematogenous infection because of greater anatomic detail, the ability to reveal marrow changes, and the better contrast between bone and soft tissue. ~9A localized area of heterogeneous signal alteration is depicted by MRI with decreased signal intensity on Tl-weighted images and increased signal intensity on T2-weighted images. In a few instances, there may be decreased signal intensity on T2-weighted imaging. The mechanism for signal intensity changes is the involvement of the marrow space with an exudative, edematous, or ischemic process producing prolongation of the T~ and T 2 relaxation times. The irregular contour of the infectious lesion may be similar to an infiltrating neoplasm. The best predictors of acute osteomyelitis are poorly defined soft-tissue planes, absence of cortical thickening, and a poor interface between normal and diseased marrow. In contrast, chronic osteomyelitis presents with a well-defined softtissue abnormality, a thickened cortex, and a relatively good interface between normal and diseased marrow. The MRI contrast studies with gadolinium enhance the detection of osteomyelitis and abscess formation. ~9

Ultrasound The ease of performing ultrasound, widespread availability, speed, and low cost compared with cross-sectional imaging, as well as the possibility of ultrasoundguided aspiration, make this technique attractive. 2~

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Fig. 8. A 3-year-old with diaphyseal osteomyelitis. Bone scan. A, Anterior delayed image of the lower extremities with increased uptake in the metaphyseal-diaphyseal region of the proximal right tibia. B, Ultrasound, sagittal scan demonstrating deep soft-tissue edema (decreased echogenicity) (arrows) adjacent to the cortex (curved arraws) with focus of cortical destruction (open arrow). C, CT, transaxial image of tibia demonstrating area of lysis with corticaF destruction along anterior margin of diaphysis.

Collections of fluid are not normally present, either in the soft tisssues or surrounding the bone (Fig. 8). If ultrasound reveals a fluid collection contiguous with the bone (i.e., without intervening soft tissue), then a bone origin of abnormal fluid collection is suggested. This correlates with the pathophysiology of the disease. With hematogenous dissemination of organisms, an acute inflammatory process is initiated in a bone. This results in vascular ischemia, edema, and bone necrosis. As the exudative process continues and tissue pressure increases, in children one may see the periosteum elevated by fluid and s u b p e r i o s t e a l abscess formation.

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Sonography cannot help one distinguish between sterile and infected fluid. The presence of joint fluid is not diagnostic of a concurrent process within the bone. Septic arthritis, obviously, may be a discrete process or may be s e c o n d a r y to seeding f r o m an u n d e r l y i n g osteomyelitis. Conversely, a sterile fluid collection may be a sympathetic process related to underlying infection in the bone.

RecommendedImagingApproach The following is a recommended imaging approach for diagnosing musculoskeletal infections in children:

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Fig. 9. A 2-month-old infant with multifocal infantile osteomyelitis. A, Radiograph, anteroposterior view with subtle change of demineralizafion (arrow) in subluxated proximal right femur. B, Bone scan, anterior delayed image of pelvis with increased uptake in right sacroiliac joint (open arrow) and increased radiotracer accumulation in proximal right femur (arrow). C, CT, transaxial image of pelvis with lyric lysion in subluxated proximal right femur. Right sacroiliac region of bone destruction not shown.

1. Anteroposterior and lateral radiographs 2. Multiphase bone scintigraphy 3. Gallium or tagged white blood cells with an equivocal bone scan 4. CT or MRI for greater anatomic detail.

Pediatric Sedation for Imaging Musculoskeletal Infection Patient motion in the uncooperative child (6 years of age or less) or the older child with inability to cooperate (cerebral palsy, etc.) can prevent the acquisition of readable images and complicate the diagnosis of the clinical problem. Sedation is sometimes necessary for those imaging procedures that require the patient to remain in a stationary position for a prolonged period. These procedures include the specialized procedures (single-photon emission computed tomography and pinhole collimated images) of bone scintigraphy as well as the whole-body skeletal scan for metastatic, infectious, and traumatic lesions. Cross-sectional imaging (CT and

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MRI) also require positioning in a narrow space and elimination of patient motion. The pediatric sedation procedures vary in each institution but usually follow the guidelines for monitoring and sedation of children as published by the American Academy of Pediatrics. 2~ The Joint Commission on Accreditation of Health Care Organizations mandates an institution-wide policy for pediatric sedation.

Distinctive Forms of Musculoskeletal Infection Septic Arthritis Septic arthritis in children is a surgical emergency. Approximately 75% of cases of septic arthritis involve the lower extremities? 2 The hip is the most common site. Infants with septic arthritis have irritability, anorexia, and fever. Local signs and symptoms are usually difficult to detect. Organisms in the neonatal period are usually coliform or gram-positive cocci. In children 6 months to 2 years of age, Haemophilusinfluenzae

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becomes the most likely organism. Most cases in older infants and children result from S. aureus. Bacteria produce enzymatic products that can lyse the cartilage and cause irreversible joint damage. The purulent material can increase enough to subluxate or dislocate the femoral head and produce vascular compromise and secondary avascular necrosis (Fig. 9). Septic arthritis has to be differentiated from transient synovitis, traumatic synovitis, hemarthrosis, rheumatic fever, juvenile rheumatoid arthritis, cellulitis, osteomyelitis, chondrolysis, Lyme arthritis, and Legg-Calvr-Perthes disease. Early in the course of septic arthritis, radiographs may appear normal, show soft-tissue derangement, or reveal dislocation or subluxation of the femoral head. Sometimes capsular swelling is apparent with obliteration and displacement of the gluteal muscle lines, and asymmetric fullness of the iliopsoas and obturator internus softtissue planes. If subluxation or dislocation of the femoral head is apparent, arthrocentesis should be peformed to remove and culture the purulent material. The infectious process can be differentiated from congenital dislocation by the lack of abnormally developed acetabulum and femoral head. Delayed removal of the purulent material and the presence of proteolytic enzymes may destroy the femoral ossification center. The appearance of sclerosis and decreased volume in the proximal femoral epiphysis usually heralds the onset of avascular necrosis. Early, less obvious collections of intra-articular fluid can be easily detected by ultrasound of the hips. If fluid is present, arthrocentesis can be performed and appropriate cultures can be obtained. Sometimes a sterile sympathetic effusion may form near a focus of osteomyelitis. Purulent material sometimes appears more echogenic than serous fluid, but the echo pattern is not reliable for determining the nature of the joint fluid. Even when ultrasound is positive for fluid, and diagnostic aspiration is performed, scintigraphy can be employed to identify an associated metaphyseal osteomyelitis or avascular necrosis of the femoral head. It is beneficial to perform whole body bone scan in young children even when symptoms appear very focal, because sometimes septic arthritis and osteomyelitis can be multifocal. In septic arthritis, the periarticular distribution of abnormal uptake is seen on both "blood-pool" and delayed images of the joint. There is symmetric uptake on both sides of the joint. 23 If the distribution of the activity within the joint capsule is not uniform or if extension beyond the joint capsule is extensive or asymmetrical, osteomyelitis is also present. When purulent material is

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within the hip joint under increased pressure in the young child, it produces a tamponade effect on the blood supply and a "cold" femoral head. The increased intra-articular pressure exceeds the venous pressure, which resuits in compression of the venous circulation and, in turn, decreased arterial supply. The ischemia is reversible if the joint is aspirated and the pressure is reduced within 12 to 24 hours. 24 Otherwise, avascular necrosis of the femoral head can be a complication the septic arthritis. Several authors have reported false-negative bone scans in patients with septic arthritis and identification of the joint infection by subsequent imaging with galliumY

RecommendedImaging Approach The following is the recommended imaging approach for septic arthritis in children: 1. Plain radiographs 2. Ultrasound 3. Bone scintigraphy to rule out associated osteomyelitis

Osteomyelitis of Infancy Localized swelling, tenderness, and failure to move the limb are usual symptoms in infancy. The systemic response to bone infection may be diminished or even absent, frequently resulting in a serious delay of diagnosis. Extensive radiographic changes can occur in infancy. Widespread periosteal reaction results from the loose attachment of periosteum to the diaphysis, the combination of joint and epiphyseal involvement from the presence of transepiphyseal arteries, and the detectable bone resorption from the scant metaphyseal trabeculae and cortex. Aspiration of a joint or bone can precede the bone scan. There is a misconception that needle aspiration will m a k e the scan falsely positive. N e o n a t a l osteomyeliits is often multifocal and, therefore, the entire skeleton should be imaged even when the symptoms are localized (Fig. 9). The sensitivity of skeletal scintigraphy for osteomyelitis has been reported to be lower in the neonate than in older children. 26,27Sensitivity is very dependent on the experience and patience of the examiner and his or her staff. Meticulous symmetric positioning of the neonate's body parts with attention to the metaphyseal/epiphyseal regions is extremely important. High-resolution pin-hole collimation is often necessary because of both the relative small size of the skeleton and the need to separate the pathologic focus from the very active physis. With the reduced amount of injected radioactivity and longer

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imaging times, sedation is sometimes necessary to reduce patient motion; this is done to increase the quality of the images and ensure that an accurate interpretation of the study is possible. When the bone scan appears normal but the clinical picture is strongly suggestive of osteomyelitis, additional scanning with a repeat bone scan in 24 to 48 hours or the adjunct of gallium may be useful. The high percentage of neutrophils and the volume of blood (20 ml) required for white blood cell labeling may not be practical in diagnosing infection in infants. Other imaging modalities are useful when the site of infection is localized. Ultrasound examination can provide guidance to where and when fluid accumulates. Cross-sectional imaging may be especially helpful when the spine or pelvis is involved (Fig. 9, C).

RecommendedImaging Approach The following is the imaging approach recommended for infants with osteomyelitis: 1. Good radiographic examination of suspected area of involvement 2. Bone scintigraphy of entire skeleton 3. Gallium scintigraphy with equivocal or normal bone scan 4. Ultrasound guidance for aspiration of fluid 5. CT or MRI if more anatomic detail is necessary

Epiphyseal Osteomyelitis Isolated epiphyseal infection in the child is a recognized entity. These patients may initially be seen with acute symptoms (febrile with painful swelling) or have a somewhat indolent clinical course. The sedimentation rate and white blood cell count may be elevated. Most of the lesions are sterile, affecting children between 2 and 4 years old. 2~When a bacterium is found, it is usually S. aureus. The transphyseal arterial connections were thought to disappear as a child approached 18 months of age; however, subsequent investigation in older children led to the identification of multiple branches of a large encircling artery (Hunter circle) perfusing the peripheral portions of the metaphysis and the entire epiphysis. 29 The epiphyseal branches are radially oriented to supply the articular and physeal cartilages and empty into radially oriented venous sinusoids that drain to the center of the epiphysis. A hemodynamic pattern of relatively slow flow in the epiphyseal sinusoids is similar to what occurs in the metaphysis. The epiphysis of the distal femur is most frequently affected. The differential diagnosis includes mainly benign neoplasms

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(chondroblastoma, osteoid osteoma, enchondroma, and, rarely, eosinophilic granuloma). In early cases, radiographs may appear normal or show an epiphyseal round or oval lytic lesion with irregular or ill-defined margination (Fig. 10, A). The more subacute and chronic lesions demonstrate a more sharply demarcated area of lysis with slightly sclerotic borders. Bone scintigraphy with the blood-pool phase, as well as high-resolution pin-hole collimation, can readily separate the metaphysis and the epiphysis from the very active physis (growth plate) and thus identify epiphyseal and epimetaphyseal locations of osseous infection (Fig. 10, B and C). Distinction of the metaphysis and epiphysis is difficult with routine delayed planar images because of the active intervening physis. CT images the bone cavity itself and associated cortical destruction, which is rarely seen on plain radiographs, that favors the diagnosis of osteomyelitis. 3~ The presence of a sequestrum or a sinus tract can also be determined by means of CT.

RecommendedImaging Approach The following is the recommended imaging approach for checking for epiphyseal osteomyelitis: 1. Plain radiographs in anteroposterior and lateral projections 2. Bone scan with delayed high-resolution magnification images 3. CT for additional anatomic detail

MetaphyseaI-Eq uivalent Infection The skeleton of a child between 6 and 16 years of age is susceptible to infection at locations that physiologically r e s e m b l e the long bone metaphyses. A m e t a p h y s e a l - e q u i v a l e n t location is defined as the portion of a flat or irregular bone that borders cartilage (apophyseal growth plates, articular cartilage, or fibrocartilage)?~ Approximately 25% of acute hematogenous osteomyelitis affects flat and irregular bones. The vascular anatomy of metaphyseal-equivalent regions is similar to the ends of long bone metaphyses and also results in sluggish blood flow. The most common organism causing the suppurative process is S. aureus in the adolescent. Before a child reaches 10 years of age, the location usually is affected by a subacute infectious process with no identifiable organism. Infections of the bony pelvis often present challenging diagnostic problems because of the vagueness and lack of specificity of the symptoms? 2 Such cases may mimic, for example, acute osteomyelitis, urinary tract

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Fig. 10. A 12-year-old with subacute osteomyelits localized to the epiphysis. A, Radiograph, anteroposterior view of left knee with question of localized area of rarefaction along the medial condyle of the distal femur (arrow). B, Bone scan, anterior soft-tissue imaging of left knee with increased uptake in the area of the joint space (septic arthritis) as well as focal increased uptake in the medial femoral condyle (arrow). C, CT, anterior pin-hole high-resolution delayed image of left knee with intense uptake of the radiotracer in medial femoral condyle.

infection, pelvic abscess, and lumbar disk disease. The hip, sacroiliac joint, ischiopubic synchondrosis, pubic bones--all can be common sites of involvement. Other metaphyseal-equivalent locations, in order of decreasing frequency, include the vertebrae, calcaneus, apophyseal center of the greater trochanter, ischium, tibia tubercle, scapula, and talus. 32 Early radiographic changes are difficult to identify in the pelvis, especially in the sacroiliac regions because of the complexity of the anatomy, the thickness of the soft tissues, and overlying air and fecal contents of the large bowel. These metaphyseal-equivalent locations are usually devoid of early radiographic changes and lend

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themselves to bone scintigraphy (Fig. 6, A). When osteomyelitis is strongly suspected and the bone scan finding is equivocal or normal, a gallium or tagged white blood cell study should be performed. CT or MRI is usually necessary to confirm the presence of a lesion involving the cortex and adjacent soft tissues (Fig. 6, C). CT can confirm the presence of a lesion involving the bone, bone marrow, and soft tissues. The typical MRI appearance of infection in metaphyseal-equivalent locations of the pelvis is a localized area of heterogeneous signal alteration, usually with decreased signal intensity on T1-weighted images and increased signal in T2-weighted images indicative of the presence of an

Curr Probl Pediatr, August 1996

.a.

Fig. 11. An 8-year-old with diskitis. A, Radiograph, anteroposterior view demonstrating loss of the disk space between T11-12 with associated soft-tissue paraspinal fullness (arrows). B, Bone scan, posterior soft-tissue image of spine with increased uptake spanning two vertebral levels in the lower thoracic spine (arrows). C, Posterior delayed image of spine with increased radiotracer accumulation at T-11, T-12, and the intervening disk space (arrows).

exudative or ischemic process in the marrow. The presence of an accompanying soft-tissue component is also clearly delineated by means of MRI. 33

Recommended Imaging Approach The following is the recommended imaging approach in cases of suspected metaphyseal-equivalent infection: 1. Plain radiographs 2. Multiphase bone scintigraphy 3. Gallium or tagged white blood cell study if bone scan normal or equivocal 4. CT or MRI

Diskitis and Vertebral Osteomyelitis Diskitis is an inflammatory process that arises in the intervertebral disk space and occurs much more commonly in children than in adults. There are two age peaks: 6 months to 4 years and 10 to 14 years? 4 Diskitis

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may represent a milder form of vertebral osteomyelitis because the anastomotic osseous arterial network in children prevents a larger portion of the vertebra from being destroyed by infarction and subsequent infection. Usually the process is indolent and the patient is not particularly ill. Back pain with a low-grade fever is usually present. Irritability and refusal to walk is common in younger children. The underlying cause is uncertain because positive cultures of blood or biopsy material are rarely found. Diskitis affects girls more often than boys (2:1 ratio). The sedimentation rate is usually elevated. Vertebral osteomyelitis is much rarer in children, usually more virulent, and with a greater number of positive cultures. In both infectious processes, the isolated organism is almost uniformly S. aureus. Diskitis is usually treated by immobilization with a rigid body cast to provide pain relief. Antibiotic therapy may be used if pain persists despite adequate immobilization

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and sustained sedimentation rate. The most cautious choice of therapy is antistaphylococcal antibiotic treatment by the intravenous route, changing to the oral route when improvement occurs, much like the approach to vertebral osteomyelitis. The first radiographic sign of disk space infection is the diminished width of the disk space (Fig. 1 1, A). Disk space narrowing is not specific for infection and can be found subsequent to t r a u m a and with Scheuermann's disease. The compromise of the disk from infection may appear in just 10 days in the younger age group or it may take 2 to 4 weeks in the older age group. The inflammatory process may be confined to the disk space or involve the adjacent vertebrae equally or asymmetrically. A lytic defect in the vertebral body may arise as a result of the infection or herniation of swollen disk material. L1-2 and L3-4 are the most common levels. The earliest radiographic change noted in vertebral osteomyelitis is focal bone loss in the superior or inferior region of the involved vertebrae adjacent to the cartilage end plate. At 6 to 10 weeks following the onset of symptoms, frank destruction of the end plates and extension of the lytic process into the central portion of the vertebral body occurs. The body becomes compressed and a paravertebral soft-tissue mass may be evident. The presence of a suppurative soft-tissue mass (abscess) is more typical of osteomyelitis than pure diskitis. Positive findings in bone scintigraphy may predate radiographic changes in cases of both diskitis and osteomyelitis by weeks. The usual scintigraphic pattern in diskitis is increased uptake in the disk space and the contiguous ends of the adjoining vertebrae on both the blood-pool and delayed bone images of the bone scan (Fig. 1 I, B and C). 35 SPECT imaging and pin-hole collimation can accurately identify the site and extent of involvement.36 Increased uptake in contiguous vertebral bodies is usually specific for diskitis, and the addition of gallium is needed only if the bone scan finding is inconclusive. 37 The gallium study should be extended to 72 hours when one is imaging for diskitis. With vertebral osteomyelitis, bone scintigraphy usually shows diffuse uptake of the radiopharmaceutical within the involved vertebra in both blood-pool and delayed images. In adults, the combination of gallium and bone scintigraphy exhibits a sensitivity of 90% and a specificity of up to 100%J ~ The indium-111 leukocyte study lacks sensitivity for vertebral osteomyelitis in adults, probably because detection of these infections is often delayed and, therefore, chronic. Because most tagged

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white cells are neutrophils, a chronic infection with a lymphocyte response will not exhibit increased uptake. A large percentage of vertebral osteomyelitis is photondeficient, or cold, on tagged white blood cell studiesJ ~ This is believed to be the result of the mass effect of edema and the purulent material in a nonexpansile area of the skeleton and the decreased number of labeled cells at the site of infection. CT examination of the spine correlates well with an abnormal site seen on scintigraphy. CT displays the irregular erosive changes in the vertebral margins and the lack of significant paravertebral mass in diskitis. Contrast-enhanced CT may exhibit hyperemia of the disk, indicative of the inflammatory/infectious process. CT may demonstrate the early osteolytic changes in the vertebral body in osteomyelitis that are not apparent on plain radiographs. It can define intraspinal or extraspinal soft-tissue components of spinal infection such as paravertebral mass, epidural collection, and psoas involvement with abscess? 8 MRI is both sensitive and specific for diskitis and osteomyelitis. 39 The MRI examination is sensitive to the change in disk hydration, which takes place early in the course of the disease (Fig. 7). In children, the signal from the disk is decreased. MRI provides better anatomic details, such as loss of disk width and indistinctness of the end plates. MRI is also helpful in identifying the paravertebral soft-issue involvement of osteomyelitis not apparent on plain radiographs or CT scans.

RecommendedImagingApproach The following is the recommended approach for imaging a child with suspected diskitis or vertebral osteomyelitis: 1. Anteroposterior and lateral radiographs of the spine 2. Multiphase bone scan or CT if abnormality is not present radiographically 3. MRI (depending on availability) or multiphase bone scan

Chronic Recurrent Multifocol Osteomyelitis

(C O)

CRMO, a multifocal inflammatory/infectious involvement of bone, is characterized by an indolent, sometimes recurrent, course (average of 6 years), lack of an identifiable pathogen, rare systemic manifestations, and a paucity of significant laboratory results (elevated white blood count or sedimentation rate). Sometimes the clinical presentation is confused with juvenile rheumatoid arthritis, but many of the sites are initially asymptomatic

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Fig. 12. A 9-year-old with chronic recurrent multifocal osteomyelitis. A, Bone scan, anterior soft-tissue image exhibiting foci of increased uptake in fourth metatarsal, base of first metatarsal and distal tibial metaphysis on the distal left lower extremity (arrows). B, Delayed anterior image with increased uptake in same areas as soft-tissue phase in distal left lower extremity (arrows). C, Radiograph, anteoposterior view of feet demonstrating tumorous sclerotic enlargement of fourth left metatarsal and rarefaction of base of first metatarsal (arrow).

but become painful with chronicity.4~Most children with CRMO are seen in the latter half of their first decade and the first half of the second decade, with females having a predominence (2:1). The patient may be initially seen with either a single lesion, followed by the development of foci, or many concurrent lesions in different phases of activity. The lack of specific clinical, laboratory, and radiographic criteria for diagnosis sometimes forces the biopsy of one or more lesions in each patient. In the more acute lesions, the histologic study reveals a greater preponderance of polymorphonuclear cells. In the older lesions there may be an admixture of inflammatory cells consisting primarily of plasma cells, macrophages, lymphocytes, multinucleated giant cells, and fibrosis. 4~ Sometimes the pain, swelling, and ten-

Curr Probl Pediatr, August 1996

derness of the lesions of CRMO are associated with palmoplantar pustulosis, a skin disease characterized by recurrent sterile pustules on the palms or soles. The treatment of CRMO consists of supportive measures. Symptomatic relief with steroid therapy, analgesics, and antiinflammatory drugs is sometimes effective. Antibiotics are not usually efficacious because no bacterial organism grows from the bone biopsy specimen. Chronic recurrent multifocal osteomyelitis can involve the epiphyses, metaphyses, diaphyses, or metaphyseal-equiva.lent locations of the skeleton. The radiographic changes vary from lytic (acute/subacute), to mixed (subacute/chronic), to completely sclerotic (chronic) (Fig. 12, C). The radiographic appearances vary according to the anatomic site. Changes in small-

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diameter and flat bones, such as the short tubular bones of the extremities, distal radius and ulna, distal fibula, clavicle, and ribs, usually are seen as small radiolucent metaphyseal lesions surrounded by more extensive periosteal reaction, sclerosis, and soft-tissue swelling. Many of the lesions, especially in the clavicle, distal radius, and ulna, extend into the diaphysis and may mimic the appearance of primary or metastatic bone malignancy. Lesions in large-diameter bones, such as the metaphyses of the femur and the tibia, vary in their radiographic pattern according to the time of presentation in the chronology of the disease process. In the more acute phase of the disease, focally destructive lucent metaphyseal lesions with little soft-tissue swelling or periosteal reaction are seen, while in the subacute or chronic phase there is a combination of subtle lysis and sclerosis. Scintigraphic evaluation of the skeleton in childhood for infection or tumor should never be localized to one portion of the skeleton. Whole body bone scintigraphy is helpful in identifying multiple lesions whether they are symptomatic or not. Scintigraphic detection often predates radiographic changes (Fig. 12, A and B). Lesions in the healing phase will also be very active on bone scan. The whole body including the hands and feet should be imaged on blood-pool and delayed images so that the characteristics of subtlely thickened growth plates reflecting metaphyseal disease and involvement of the epiphyses can be identified. Singlephoton emission computed tomography imaging may have to be performed to confirm lesions of the ribs, pelvis, and vertebral column. Pin-hole collimation assists in the d i f f e r e n t i a t i o n of epiphyseal and metaphyseal lesions. Radiographic correlation, which may at times necessitate the use of CT or MRI, should be undertaken. Without pathognomonic findings, the diagnosis is one of exclusion. The most commonly affected sites are the distal tibial and femoral metaphyses, followed by the clavicle and forearm bones (radius and ulna). Other reported skeletal sites have included the mandible, ribs, humerus, radius, metacarpals and metatarsals, talus, pelvis, and sternum. 42Radiographic correlation of the sites of increased uptake can often aid in the diagnosis of CRMO by defining lesions in the distal appendicular skeleton (tubular bones of the hands and feet, bilateral symmetric involvement of the distal radii, ulnae, and tibiae) and in the axial skeleton (involvement of the clavicle and mandible).

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This lesion distribution mitigates against the diagnosis of metastatic disease because in older children the marrow-containing portions of the skeleton are usually proximal appendicular and axial. In the differential are metastases of Ewing's sarcoma, neuroblastoma, leukemia, and histiocytosis. These infiltrating processes usually frequent the marrow-containing bones of the skeleton. The coexistence of lesions in different phases (acute, subacute, and chronic) in the same individual is unusual for aggressive malignancy. Recognition of the condition is important to avoid treatment with antibiotics and repeated operations. Complete sclerosis and slow regression of the lesions with ultimate healing may occur, but complications may arise because of the prolonged presence of these hyperemic lesions. These complications include premature physeal closure with shortening or angular deformity of a long bone. Some bones maintain enlarged tumor-like appearances for prolonged periods. The healing process may take several years.

Recommended Imaging Approach The following is the recommended imaging approach for suspected CRMO: 1. Multiple blood-pool images of the appendicular skeleton and delayed images of the whole skeleton 2. Plain radiologic correlation of the multiple areas of increased uptake

Sickle Cell Disease Skeletal complications of bone frequent S-S and S-C disease. The hemoglobin S is sensitive to hypoxemia, resulting in decreased solubility from polymerization of hemoglobin S. Erythrocytes with the highest concentration of hemoglobin S become viscous and sickle abruptly. As hypoxemia worsens, the cells compromise microvascular flow and cause infarction. Necrotic bone is a fertile site for secondary infection. Immunologic deficiencies also make the sickle cell disease patients more susceptible to infection. S. a u r e u s is the usual pathogen, but salmonella (an unusual organism in the normal population) is frequently present in bone infections in sickle cell disease. Osteomyelitis is difficult to distinguish clinically from bone infarct. Hyperplasia of bone marrow can cause squaring of the metacarpals in children beginning at about 6 months of age and Erlenmeyer flask deformities in the long bones of older children. In long bones, radiographs

Curr Probl Pediatr, August 1996

during an acute painful episode may be normal or show nonspecific changes (deep soft-tissue swelling). With time, the medullary portions of long bones may exhibit patchy lucency and sclerosis. A bone-within-abone appearance may result from the healing of an infarct. The bone scan is initially sensitive but may give variable findings, particularly if it is performed more than a week after the onset of symptoms. With the passage of time, increased uptake may result from either osteomyelitis or healing avascular necrosis. Similarly, a cold defect may result from osteonecrosis, but is occasionally caused by acute osteomyelitis. In patients with repeated episodes of bone infarcts, the bone scan shows a patchy pattern that makes differentiation of osteomyelitis and infarction particularly difficult. To diagnose osteomyelitis in sickle cell disease, one must often use more than one radiotracer and, therefore, two sequential studies. The combination of marrow scanning (using technetium-99m sulfa colloid) and the bone scan has been utilized to differentiate bone infarction from osteomyelitis. In patients with sickle cell disease, the marrow is normally expanded throughout the skeleton because of the underlying anemia. At a site of infarction, there may be normal, decreased, or increased uptake of bone tracer, depending on the age of the infarction; however, an acute infarction always has decreased marrow uptake. A normal marrow scan in an area of suspected acute osteomyelitis on the bone scan usually means the presence of bone infection. 43 It is not possible to distinguish the decreased uptake of a sterile infarct from an infected infarct on the marrow scan. Normalization of marrow uptake does occur, but this may take weeks or months. Gallium imaging may result in nonspecific increased uptake in a region of osteoblastic activity because of its bone tracer properties. The lack of or mild increased uptake of gallium helps to exclude osteomyelitis. Gallium scanning can be used to differentiate infarction from osteomyelitis in combination with the bone scan. When the combination of bone radiotracer and gallium imaging are used, the pattern of accumulation of each agent is compared. If a bone scan is photon-deficient, or cold, in acute osteomyelitis, gallium is useful by showing increased uptake in osteomyelitis and normal uptake in infarction. When the uptake of gallium is incongruent with the bone tracer uptake, then the diagnosis of osteomyelitis should be entertained. 44 When the distribution of the activity is geographically

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similar, infection is implied only when the relative gallium uptake is greater the bone tracer uptake. This determination is very subjective and not always reliable. Tagged white blood cell imaging (tagged either with indium or technetium) may be effective for detecting infection in a patient with previous bone infarcts and equivocal areas on bone scan. The reticuloendothelial system of the marrow may be visualized with the white blood cell imaging because sulfur colloid is used in their preparation. Complicated cases with areas of hyperplastic marrow, therefore, may also be confusing. The white blood cell scan, unlike gallium scintigraphy, does not contend with uptake related to healing bone. The tagged white blood cell study should probably be reserved for instances when the diagnosis of osteomyelitis is strongly suspected but cannot be established by usual methods. Further reportings are necessary to clarify the accuracy of tagged white blood cell scintigraphy in sickle cell disease. 45 MRI shows areas of infarction quite distinctly because of changes in the signal intensity of the marrow. Normal hyperplastic hematopoietic marrow in the patient with sickle cell anemia is decreased in signal intensity on both short and long TI- and T,-weighted images. The edema accompanying marrow infarction can convert the low signal of TTweighted images to high signal on T 2weighted images similar to osteomyelitis, a5 Chronic infarcts are of low signal intensity on both TI- and T 2weighted images. 46

RecommendedImagingApproach The following is the recommended imaging approach for suspected cases of sickle cell disease: 1. Plain radiographs 2. Bone scan 3. If bone scan is positive, consider aspiration or the addition of gallium or tagged white blood cell scintigraphy.

Conclusion There is not one specific imaging approach to infection of the musculoskeletal system because infection affects the pediatric musculoskeletal system in many different ways. Different imaging schemes have to be used for different clinical problems. The scheme may vary according to the location of the site of infection, the age of the patient, and the amount of time the infection has been affecting the musculoskeletal system. The diagnosis may require one or more imaging mo-

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dalities. The imaging armamentarium includes plain radiography, nuclear medicine, cross-sectional imaging, and ultrasound. The imaging choice may also be affected by the expertise of the imaging individuals. Other factors that affect the imaging decision include the cost, the need for sedation, and the radiation exposure. Prompt, accurate diagnosis and adequate treatment should outweigh these other factors. Prevention of the sequelae will reduce the ultimate cost of the disease.

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45. Fernandez-Ulloa M, Vasavada PPPJ, Black RR. Detection of acute osteomyelitis with indium-11 labeled white blood cells in a patient with sickle cell disease. Clin Nucl Med 1989; 14:97-100. 46. Rao VM, Fishman M, Mitchell DG, et al. Painful sickle cell crisis: bone marrow patterns observed with MR imaging. Radiology 1986;161:211-5.

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