| March 2005 Case of the Month |
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Compiled By: Roel Galope, D.O.
Clinical Information: 46-year-old female, evaluate sinus tarsi, pain at the lateral malleolar region.
Findings:
Axial and sagittal T1 and T2 weighted images reveal well defined loose bodies of low to intermediate signal within a thick walled subtalar anterior capsulosynovial cyst. Arthrosis of the calcaneocuboid joint with adjacent fibrovascular osseous stress reaction is also observed.
Diagnosis: Synovial Osteochondromatosis, Primary versus Secondary
Synovial Osteochondromatosis is an uncommon benign self-limiting disorder characterized by proliferative and metaplastic changes in the synovium with formation of intrasynovial cartilaginous or osteocartilaginous nodules. It is also known as synovial chondromatosis or joint chondroma.
It usually occurs in the 3rd to 5th decades of life and twice as common in men. It is a slowly growing intraarticular process, presenting with a several year history of progressive pain and progressive limitation of motion and locking. It may be accompanied by hemorrhagic joint effusion.
The most common joint involved is the knee (most common with >50%, in 10% bilateral) followed by the elbow, hip, shoulder, ankle and wrist. It is usually monoarticular. Occurring mostly within joints, it can occasionally arise from a tendon sheath, ganglion, or bursa.
Three phases of the disease are identified. The initial phase is comprised of metaplastic cartilaginous masses within the synovium. The transitional phase is when cartilaginous nodules detach from the involved synovium forming free bodies. The inactive phase is when the synovial proliferation has resolved but loose bodies remain, usually with variable amounts of joint fluid.
Prior to the development of calcification or ossification, conventional radiographs show only an effusion within the joint. In tighter joints such as the hip, well-defined pressure erosions of the periarticular bony cortex may be seen.
The MRI appearance is variable and depends on the relative preponderance of synovial proliferation and loose bodies formation and on the extent of calcification or ossification. Synovial masses of lobulated borders, with or without associated intraarticular loose bodies, are the most common MRI finding. Unmineralized synovial masses exhibit high signal intensity on T2-weighted images, reflecting hyaline cartilage content. Foci of signal void due to mineralization within synovial masses are common but only sometimes show low signal intensity on T2-weighted images. Signal voids are more conspicuous on gradient-echo sequences.
Calcified loose bodies appear as a nodular signal void, whereas ossified loose bodies show signal intensity characteristics of marrow fat centrally and of cortical bone peripherally.
Long-standing disease may lead to degenerative arthritis, from chronic mechanical irritation and destruction of articular cartilage by loose bodies. Cases of malignant dedifferentiation to chondrosarcoma have occurred. Treatment in the initial or transition stage with synovectomy is usually successful. Recurrence can occur if synovial rests are left behind. Treatment of the inactive phase simply comprises of removal of the loose bodies.
Secondary osteochondromatosis is due to joint surface disintegration from another underlying cause such as rheumatoid arthritis, neuropathic arthropathy, tuberculous arthritis, degenerative joint disease.
Main differential considerations for synovial lesions in the knee include, diffuse or focal villonodular synovitis, diffuse or focal pigmented villonodular synovitis, primary synovial chondromatosis, and lipoma arborescens. The table below reveals the differences in MRI findings for these lesions.
MR Characteristics of Synovial Lesions
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Diffuse or focal villonodular synovitis |
Diffuse or focal pigmented villonodular synovitis |
Primary synovial chondromatosis |
Lipoma arborescens |
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Villous or lobulated masses |
Villous or lobulated masses |
Effusion
Capsulosynovial thickening |
Villous or lobulated masses |
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Intermediate T1
Intermediate-hyperintense T2 |
Hemosiderin
Hypointense T1
Intermediate-hypointense T2 |
Loose body signal
Hypointense T1
Intermediate-hypointense T2 |
Fat signal
Uniform hyperintense T1
Intermediate-hypointense T2 |
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Enhancement |
Enhancement |
No enhancement |
No enhancement |
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Tends to extend into the semimembranosus-gastrocnemius bursa |
Tends to extend into the semimembranosus-gastrocnemius bursa |
Loose bodies can be found within decompression cysts |
Suprapatellar bursa |
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Effusion
Capsulosynovial thickening |
Effusion
Capsulosynovial thickening |
Effusion
Capsulosynovial thickening |
Effusion
Capsulosynovial thickening | Adapted from Gamuts and Pearls in MRI & Orthopedics, Pomeranz 1997 |
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References:
Chan K, Pathria M. Idiopathic Synovial Osteochondromatosis. MRI of the Musculoskeletal System, A Teaching File 2001:136-137
Narváez J, Ortega R, De Lama E, Roca Y, and Vidal N. Hypointense Synovial Lesions on T2-Weighted Images: Differential Diagnosis with Pathologic Correlation. Am. J. Roentgenology, Sep 2003; 181: 761 - 769.
Sheldon P, Forrester D, and Learch T. Imaging of Intraarticular Masses. RadioGraphics 2005; 25: 105-119.
Stoller DW. Idiopathic Synovial Osteochondromatosis. Chapter 10. Magnetic Resonance Imaging In Orthopedic Sports Medicine, 2nd ed. 1997:815-816. | |
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