Spectrum of Synovial Pathologies: A Pictorial Assay Sriram Jaganathan, MD,a Ankur Goyal, MD,a Ankur Gadodia, MD,a Shishir Rastogi, MS,b Ravi Mittal, MS,b and Shivanand Gamanagatti, MDc
The synovium, a specialized vascular tissue, lines the diarthrodial joints, bursae, and tendon sheaths of the body. It helps in nourishment of articular structures. The synovium is affected by a variety of disorders that can be either localized or systemic. Although normal synovium is barely perceptible on magnetic resonance imaging, it provides an excellent imaging modality for the evaluation of pathologic processes involving the synovium. The pathologic processes affecting the synovium include 1 of the following etiologies: inflammatory, infectious, degenerative, traumatic, or neoplastic and tumor-like conditions. In this article, we discuss the magnetic resonance imaging technique and the sequences used in the evaluation of synovial pathologies and review the characteristic imaging findings of specific conditions thus narrowing the differential diagnoses.
The pathologies affecting synovium can be classified according to the etiology that includes inflammatory as in rheumatoid and other seronegative arthritis, infectious as in tuberculosis and other nonspecific bacterial infections, degenerative as in osteoarthritis, traumatic as in posttraumatic synovitis, hemorrhagic arthropathies, especially in hemophiliacs, and neoplastic as in synovial hemangioma, synovial sarcoma. Other tumor-like conditions include pigmented villo nodular synovitis, synovial chondromatosis, and lipoma arborescens.
Rheumatoid Arthritis Synovium is a thin membrane lining the joint capsule and attaches to the margins of the articular surfaces and periphery of articular cartilage. Synovial membrane lines the diarthrodial joints, bursae, and the tendon sheaths. It secretes synovial fluid that helps in lubrication and nourishment. Normal synovium is not perceptible on any imaging modality. The imaging modalities useful in the diagnosis of synovial pathologies are ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI), among which MRI scores higher than the other modalities. Although the MRI findings are nonspecific in certain conditions, it helps in narrowing down the differential diagnosis. From the aDepartment of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India; bDepartment of Orthopaedics, All India Institute of Medical Sciences, New Delhi, India; and cDepartment of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi, India. Reprint requests: Shivanand Gamanagatti, MD, Department of Radiodiagnosis, Room 66, All India Institute of Medical Sciences, New Delhi 110029, India. E-mail:
[email protected]. Curr Probl Diagn Radiol 2012;41:30-42. © 2012 Mosby, Inc. All rights reserved. 0363-0188/$36.00 ⫹ 0 doi:10.1067/j.cpradiol.2011.07.002
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Rheumatoid arthritis is a chronic progressively destructive inflammatory arthropathy affecting multiple joints in a symmetrical fashion primarily affecting the synovium. It affects all age groups, more commonly 20-55 years, with female preponderance. The disease process has periods of remission and exacerbation; most often it is progressive, ultimately resulting in multiple deformities. Permanent disability occurs in 10%-20% of the affected population.1 The disease first affects the synovium, resulting in synovial proliferation and inflammatory changes followed by involvement of the articular cartilage and bones. The clinical diagnosis is facilitated using diagnostic criteria as given by the American Rheumatism Association. The main use of radiographs is to demonstrate bony changes like osteopenia, joint space narrowing, and erosions that occur in late stages of rheumatoid arthritis (Fig 1). Early changes like synovitis and effusion are demonstrated well on MRI.2 MRI, apart from demonstrating the synovial proliferation, demonstrates periarticular soft tissue inflammation, inflammation involving the ligaments, tendons,3 and bone marrow. Apart from T2W fast spin-echo se-
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FIG 1. Posteroanterior radiograph (A) of bilateral hands of a 50-year-old woman with rheumatoid arthritis shows diffuse osteopenia, narrowing of intercarpal (white arrow), radiocarpal and carpo-metacarpal joint space with articular surface erosions (black arrow). T2W fat-suppressed (B) MRI of a different patient with rheumatoid arthritis shows diffuse synovial thickening (asterisks) involving the intercarpal joints.
FIG 2. Axial (A, B) and sagittal (C, D) T1W postcontrast MRIs of a 35-year-old woman with rheumatoid arthritis of the elbow show thickened enhancing synovium in radio-ulnar joint (black arrowhead) and elbow joint (black arrow).
FIG 3. Coronal (A, B) MRIs of the same patient as in Fig 2 with elbow rheumatoid arthritis show hyperintensity on STIR (black asterisk) and hypointensity on T1W (white asterisk) non-fat-suppressed images, suggesting bone marrow edema. Bony erosions are noted in the ulnar articular surface (white arrow).
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FIG 4. Lateral radiograph (A) of a 25-year-old man with knee pain and swelling shows increased soft tissue in the supra-patellar region (white arrow). Axial (B), coronal (C), and sagittal (D) T1W postcontrast MRIs show diffuse irregular synovial thickening and enhancement (black arrows) with joint effusion (asterisk). No bony erosions are seen. Synovial biopsy showed caseating granulomas, suggesting tuberculous synovitis.
FIG 5. Sagittal (A, B) and axial (C, D) MRIs of a 19-year-old woman with unilateral knee pain and fever show diffuse synovial thickening and enhancement (black arrow) on T1W postgadolinium images with erosion of patella (white arrows). Aspirated joint effusion (asterisk) shows evidence of tuberculosis.
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FIG 6. Coronal T1W precontrast (A) and postcontrast (B) MRIs of a 30-year-old man show synovial thickening and enhancement (black arrows) along the extensor tendons of the right hand, suggesting tenosynovitis.
FIG 7. A 17-year-old boy with hemophilia presented with swelling and deformity of the right knee. Anteroposterior radiograph (A) shows widening of the intercondylar notch (arrowhead), epiphyseal overgrowth, osteopenia, and destruction of the articular surface (black arrow) involving the right knee joint. The left knee joint (B) is normal. These features are diagnostic of hemophilic arthropathy.
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FIG 8. Sagittal T1W (A), sagittal T2W fat-suppressed (B), axial and sagittal gradient echo (C, D) MRIs of a 20-year-old man with hemophilic arthropathy show hypointense proliferated synovium (white arrows) and blooming on gradient echo images (asterisk). Note is made of joint effusion.
quences, T2W gradient echo sequences are useful in demonstrating synovial proliferation.4 Gadolinium-enhanced MRI demonstrates synovial proliferation much better than other sequences because of the superior differentiation between the joint fluid, cartilage, and synovium5,6 (Fig 2). Bone marrow edema and articular surface erosions are also well demonstrated on MRI (Fig 3). Postgadolinium sequence can also show synovial enhancement in normal subjects, which is a potential pitfall. Dynamic gadolinium-enhanced sequences improves the postcontrast studies, demonstrating more rapid synovial enhance-
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ment (30-60 seconds following injection) in active disease.1,7
Infectious Arthritis Arthritis indicates an inflammatory process localized to the joint, which can be septic because of an infectious cause or nonseptic. It may present with rapidly progressive onset or may be insidious. Early diagnosis of infectious arthritis is essential in preventing permanent joint deformity. Imaging findings have been described on radiographs, ultrasound, and MRI.8
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FIG 9. Eleven-year-old male patient presented with swelling of right knee joint. Lateral radiograph of the right knee (A) shows nonspecific soft tissue in the suprapatellar location (black arrowhead). Sagittal T1W (B, C) and T2W fat-suppressed MRIs (D, E) show the soft tissue mass to be hypointense on T1W images (black arrow), heterogenously hyperintense on T2W fat-suppressed images (white arrow). There are admixed areas of hyperintensities (foci of fat, white arrowhead) and linear hypointensities (septa) on T1W images. The lesion was confirmed to be synovial hemangioma on histopathology.
FIG 10. Coronal T2W fat-suppressed images (A, B) of the same patient as in Fig 9 show the heterogenously hyperintense synovial hemangioma (white arrows).
MRI cannot differentiate septic from nonseptic arthritis with accuracy but can suggest a difference. Although soft tissue swelling can be demonstrated early on radiographs, bone marrow and synovial involvement cannot be demonstrated and early bony changes are appreciated only after 1-2 weeks in pyogenic infection and may take months in tuberculosis.9 Synovial thickening with enhancement (Figs 4 and 5), soft
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tissue edema, and bone marrow edema with enhancement suggests an infective etiology.10 Joint effusion is a nonspecific finding that can be absent in septic arthritis.11 However, joint effusion, which is septated or with debris, signifies an infective process and aspiration should not be delayed in view of MRI. The presence of abscess, demonstrated on postgadolinium sequences as peripherally enhancing lesion around the
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FIG 11. Anteroposterior (A) and lateral radiographs (B) of left knee of a 20-year-old man who presented with knee pain and swelling for 3 months show soft tissue swelling in the medial aspect of the left knee joint (black arrow) with eccentrically located calcification (black arrowheads).
FIG 12. Coronal (A) and axial (B) T1W MRIs of the same patient show a well-defined lobulated hypointense lesion (white arrow) in the medial aspect of the left knee. The lesion (black arrow) shows heterogenous signal (triple sign, showing low-, intermediate-, and high-signal intensity) on T2W (C) and STIR (D) images. The calcific focus is hypointense (black arrowhead) on TIW, T2W, and STIR images. Histopathology revealed synovial sarcoma.
joint, suggests an ongoing infective process. Inflammation involving the synovium along the tendon sheaths is referred to as tenosynovitis, which is also better appreciated on postcontrast TIW MRIs (Fig 6).
Hemophilic Arthropathy Hemophilia is an X-linked inherited disorder that occurs because of a coagulation defect. Hemorrhage
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occurs most commonly in the musculoskeletal system and is particularly common in joints, followed by soft tissue and bones.12 Recurrent bleeds are common, resulting in articular and periarticular abnormalities. Early findings like joint effusion or hemarthrosis are demonstrated well on MRI; however, they are nonspecific. Articular and periarticular changes that occur because of frequent bleeds include hemosiderin deposition and synovial hypertrophy. In later stages, there
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FIG 13. Coronal (A-E) and axial (F) MRIs of left shoulder of a 40-year-old woman show villous proliferation of the synovium, which is hypointense (white arrow) on T1W (A) and intermediate signal intensity (asterisk) on T2W (B, C) and GRE (D-F) images. Multiple foci of T2W hypointensity (black arrowheads) in the proliferated synovium with blooming (black arrowheads) on GRE images suggest hemosiderin deposition and foci of hyperintensity on T1W (black arrow) image, indicating hemorrhage. Note is made of moderate joint effusion. These features are suggestive of pigmented vilonodular synovitis.
is epiphyseal overgrowth, early closure of physeal plate, and destructive changes.7 Plain radiograph shows epiphyseal overgrowth, widened intercondylar notch, and other destructive changes (Fig 7). The classical features on MRI include hypointense foci on both T1W and T2W sequences with blooming artifact on gradient-echo sequences, suggesting hemosiderin deposition (Fig 8). Synovial hypertrophy is well appreciated on postgadolinium T1W sequences. Thus, gradient echo sequences, which demonstrate intraarticular blood products, and contrast-enhanced sequences T1W, which demonstrate synovitis and effusion, help in early treatment planning.7
Synovial Hemangioma Synovial hemangioma is a rare benign tumor of intra-articular or juxta-articular origin. They usually occur in children and adolescents, presenting with pain and swelling. Conventional radiograph shows nonspe-
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cific soft tissue swelling.13 Sonography shows a heterogenous lesion with cystic spaces. MRI is the modality of choice, which shows intermediate signal intensity mass lesion on T1W sequence and hyperintense lesion on T2W sequence.7 Low-signal intensity channels or septa might be seen within the lesion with foci of intralesional fat (Figs 9 and 10). Postgadolinium T1W sequence shows homogenous/heterogenous intense enhancement.
Synovial Sarcoma Synovial sarcoma is the fourth most common malignant soft tissue tumor occurring commonly in the para-articular locations, such as tendon sheaths, bursae, or joint capsule. Rarely, it occurs in the intraarticular region. The tumor presents in adolescence or young adults and usually involves the extremities (80%-95%) and is more common in the lower limbs.14 Other rarer sites include the chest, head and neck,
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FIG 14. Anteroposterior and lateral radiographs (A, B) of the right knee joint of a 35-year-old man show increased soft tissue (asterisk) in the articular and periarticular location with multiple well-defined loose bodies (black arrow) seen in the medial side of the joint.
abdomen, and pelvis. The radiograph is usually nonspecific, showing round to oval juxta-articular soft tissue masses and calcification in up to 30%. These calcifications are often eccentric or peripheral within the soft tissue mass and nonspecific in appearance (Fig 11). Sonography shows lobulated hypoechoic soft tissue masses. Although CT can show a heterogenous soft tissue mass with areas of necrosis/hemorrhage and bony changes with calcification, MRI is the optimal modality for evaluation. The lesion is usually well-defined and heterogenous to uniform lowsignal intensity on T1W with a marked heterogeneity on T2W sequences. The characteristic heterogeneity, that is, the presence of low-, intermediate-, and highsignal intensity on T2W sequences, which is called “triple sign,” and the multiloculation with internal saptae suggest the diagnosis of synovial sarcoma (Fig 12). This heterogeneity in the lesion is because of the presence of solid/cellular elements giving intermediate signal, hemorrhage, or necrosis giving high signal intensity, and calcification or fibrosis giving low signal intensity.14 The lesions may also show fluid-fluid levels (due to hemorrhage), bone erosion, marrow invasion, invasion of adjacent soft tissue, and intra-articular extension. Postgadolinium T1W sequences demonstrate heterogenous enhancement.
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Pigmented Villonodular Synovitis Pigmented villonodular synovitis (PVNS) is a rare benign neoplastic process in which there is synovial hypertrophy characterized by villous, nodular, and villonodular proliferation and hemosiderin deposition. These lesions are further classified as localized or diffuse. Age of presentation is in the third to fifth decades of life. Localized intra-articular form occurs exclusively in the knee joint. The diffuse intra-articular form of PVNS most frequently affects the large joints, most commonly the knee and hip. Imaging manifestations, especially MRI of PVNS, are frequently characteristic of the disease process. Radiographic and sonographic features are often nonspecific. In diffuse intra-articular PVNS, radiographs demonstrate joint effusion, extrinsic erosion of bone and subchondral lucent areas (with sclerotic rim) on both sides of the joint, preservation of joint space, soft tissue swelling, absence of calcification, and normal bone mineralization.15 MRI reveals T2 hyperintense joint effusion with lobulated synovial thickening, which may be plaquelike or nodular, localized or diffuse, and demonstrating low- to intermediate-signal intensity on both T1W and T2W sequences. Gradient-echo sequences confirm the presence of hemosiderin, which appears as prominent “blooming” of low-signal intensity due to magnetic susceptibility artifact (Fig 13). This low signal on
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FIG 15. Sagittal and axial MRIs (A-D) of a 35-year-old man show synovial thickening (black arrowhead, A, C) with multiple well-defined intra-articular loose bodies of uniform size. These are hyperintense on T1W (black arrow in A, C, D) image with hypointense center suggesting calcification (white arrowhead) and hypointense on GRE (white arrow in B) image. These are chondral loose bodies containing fatty marrow (in the process of ossification) and foci of calcification. These features suggest primary synovial chondrometaplasia.
FIG 16. Anteroposterior and lateral radiographs (A-C) of bilateral knee joints of a 55-year-old man show narrowing of joint space in both sides. Multiple large variable sized osteophytes (black arrow) with loose bodies are seen in both joints.
T2W and especially GRE sequences, indicating hemosiderin, is virtually pathogonomic of PVNS, as other lesions showing similar findings are synovial hemangioma and hemophiliac arthropathy.16 The proliferated synovium also exhibits prominent contrast enhancement on post gadolinium T1W sequences.
Synovial Chondromatosis Primary synovial chondromatosis is a monoarticular benign neoplastic process representing chondroid metaplasia in the joint synovium with resultant formation of multiple intra-articular chondral bodies. If there is the presence of joint abnormalities (mechanical or arthritic), which may cause intra-articular chondral bodies, it is termed secondary synovial chondromatosis. Radiographs reveal multiple intra-articular calcifications or well-defined osteochondral loose bodies typically distributed evenly throughout the joint in 70%-95% cases (Figs 14 and 15). These calcifications
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are characteristically innumerable and similar in size and shape. Typical chondroid ring-and-arc pattern of calcification is also common. Fragments may mature further and undergo enchondral ossification. Disuse osteopenia, joint effusion, and extrinsic erosions of bone may be seen. Secondary synovial chondromatosis also reveals osteochondral intra-articular bodies; however, these are fewer in number and more variable in size (suggesting various times of origin).17 In addition, several rings of calcification may be identified in these bodies on radiographs, compared with the single ring seen in primary disease. Radiographic alterations associated with the underlying joint abnormality (most commonly, osteoarthritis) are also apparent and allow secondary disease to be distinguished from primary synovial chondromatosis (Figs 16 and 17). CT is the optimal imaging modality to detect and characterize calcification in the vast majority of cases.
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FIG 17. Sagittal MRIs (A-F) of the same patient show multiple variable sized loose bodies that are hyperintense on T1W (black arrow in A, B) images with thin hypointense rim, hypointense on fat-suppressed T2W (white arrow in C, D) images, and exhibit blooming on GRE (white arrowhead in E, F) images. These features of mature marrow in the variable sized loose bodies suggest the diagnosis of secondary synovial chondrometaplasia.
FIG 18. Axial (A, B) and sagittal (C, D) T1W images of a 12-year-old male child show frond-like synovial proliferation, which is hyperintense (black arrow in A, C) on T1W non-fat-suppressed sequences and hypointense (white arrow in B, D) on fat-suppressed T1W sequences, suggesting lipomatous synovial proliferation, diagnostic of lipoma arborescence. Note is made of joint effusion (arrowheads).
The characteristic pattern on MRI is lobulated, homogeneous, intermediate, intra-articular signal intensity similar to that of muscle on T1-weighted images, with high-signal intensity on T2-weighted images and focal
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areas of low-signal intensity on all pulse sequences.18 These areas of signal void correspond to regions of calcification on radiographs or CT scans and became more conspicuous on gradient-echo MRI owing to
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FIG 19. Sagittal T1W (A, B) and T2W fat-suppressed (C) MRIs of a 30-year-old man with pain and difficulty in walking show multiple T1W hypointense lesions (black arrows) along the plantar flexor tendons of the foot. The lesions are of intermediate- to high-signal intensity on T2W FS images (white arrow). On resection, the lesions were proved to be giant cell tumors of tendon sheath on histopathology.
FIG 20. Axial (A, B) and sagittal (C, D) MRIs of a 45-year-old man showing a well-defined lesion hypointense on T1W (black arrow) and hyperintense on T2W image (white arrow) posterior to the head of gastronemius muscle, suggestive of Baker’s cyst.
magnetic susceptibility effects. The other less common pattern is multiple well-defined osteochondral loose bodies with fatty marrow (T1W hyperintense) and foci of calcification (Fig 15).
Lipoma Arborescens Lipoma arborescens (diffuse articular lipomatosis) is a rare idiopathic, benign disorder characterized by villous lipomatous proliferation of the synovium. Typically, the disease is monoarticular. Plain radiographs may detect fatty lucencies within a soft tissue lesion, although the associated effusion predominates. Coexistent degenerative changes are frequently present. MRI is the modality of choice for diagnosis. At MRI, the villous lipomatous proliferation demonstrates signal characteristics of fat on all sequences, hyperintensity on both T1W and T2W sequences, and suppression on fat-saturated images (Fig 18).19
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Miscellaneous Lesions Giant cell tumor of tendon sheath is a benign soft tissue tumor arising from tendon sheath or periarticular soft tissues of small joints, most commonly involving the hands.20 The lesion is seen closely associated with the tendon, hypointense on T1W images, and intermediate to hypointense on T2W images because of the fine hemosiderin granules and abundant matrix collagen in it (Fig 19). Synovial cysts are fluid-filled para-articular lesions that occur secondary to inflammation as in rheumatoid arthritis, trauma, or osteoarthritis. Most common locations are the knee and hip but can occur anywhere. The most common synovial cyst encountered in clinical practice is the Baker’s cyst (Fig 20), located in the gastrocnemius semimembranous bursa.
Conclusions MRI is the modality of choice in the evaluation of diverse synovial pathologies with characteristic find-
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ings in specific conditions. Although definitive diagnosis cannot be achieved in certain conditions, it helps in narrowing down the differentials. A combination of features in radiographs, CT, and MRI should be sought in conditions with a diagnostic dilemma.
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