Synovial chondromatosis of the hip. Evaluation with air computed arthrotomography

Articular abnormalities that may mimic arthritis

There are numerous abnormalities that present with similar signs and symptoms to arthritis. In this article some of these conditions that can masquerade as arthritis are discussed. Synovial osteochondromatosis is an uncommon benign disorder marked by the metaplastic proliferation of multiple cartilaginous nodules in the synovial membrane of the joints, bursae, or tendon sheaths. Pigmented villonodular synovitis, also known as diffuse-type tenosynovial giant cell tumor, is a locally destructive fibrohistiocytic proliferation, characterized by many villous and nodular synovial protrusions which affects the joints. Synovial hemangioma is a rare benign lesion whose pathogenesis is still unclear. It commonly affects the knee joint, although the other articulations, such as elbow, wrist, and ankle may also be involved. Lipoma arborescens, also known as villous lipomatous proliferation of the synovial membrane, is a rare intra-articular disorder characterized by a non-neoplastic lipomatous proliferation of the synovium. The term "arborescens" refers to the characteristic tree-like morphology of the lesion, which resembles a frond-like mass.

Imaging of Synovial Chondromatosis with Radiologic-Pathologic Correlation

Primary synovial chondromatosis represents an uncommon benign neoplastic process with hyaline cartilage nodules in the subsynovial tissue of a joint, tendon sheath, or bursa. The nodules may enlarge and detach from the synovium. The knee, followed by the hip, in male adults are the most commonly involved sites and patient population. The pathologic appearance may simulate chondrosarcoma because of significant histologic atypia, and radiologic correlation to localize the process as synovially based is vital for correct diagnosis. Radiologic findings are frequently pathognomonic. Radiographs reveal multiple intraarticular calcifications (70%-95% of cases) of similar size and shape, distributed throughout the joint, with typical "ring-and-arc" chondroid mineralization. Extrinsic erosion of bone is seen in 20%-50% of cases. Computed tomography (CT) optimally depicts the calcified intraarticular fragments and extrinsic bone erosion. Magnetic resonance (MR) imaging findings are more variable, depending on the degree of mineralization, although the most common pattern (77% of cases) reveals low to intermediate signal intensity with T1-weighting and very high signal intensity with T2-weighting with hypointense calcifications. These signal intensity characteristics on MR images and low attenuation of the nonmineralized regions on CT scans reflect the high water content of the cartilaginous lesions. CT and MR imaging depict the extent of the synovial disease (particularly surrounding soft-tissue involvement) and lobular growth. Secondary synovial chondromatosis can be distinguished from primary disease both radiologically (underlying articular disease and fewer chondral bodies of variable size and shape) and pathologically (concentric rings of growth). Treatment of primary disease is surgical synovectomy with removal of chondral fragments; recurrence rates range from 3% to 23%. Malignant transformation to chondrosarcoma is unusual (5% of cases) and, although difficult to distinguish from benign disease, is suggested by multiple recurrences and marrow invasion. Recognizing the appearances of primary synovial chondromatosis, which reflect their underlying pathologic characteristics, improves radiologic assessment and is important to optimize patient management.

Primary synovial osteochondromatosis of the hip: extracapsular patterns of spread

OBJECTIVE

To identify patterns of extracapsular extension of synovial osteochondromatosis of the hip.

DESIGN AND PATIENTS

Seven cases of synovial osteochondromatosis of the hip were retrospectively reviewed. Imaging performed included conventional radiography ( n=7), arthrography ( n=1), CT ( n=3) and MR imaging ( n=3). Disease extent on imaging was assessed for each patient and the presence of intra-articular effusion, capsular abnormality and osteochondral bodies recorded. The presence and distribution of extra-articular spread was also assessed and correlated with the surgical findings. In all cases diagnosis was confirmed by biopsy, with all patients undergoing tumor resection with or without synovectomy.

RESULTS

In five cases (5/7) disease extended beyond the hip capsule, while the remaining two cases (2/7) were confined to the hip joint. These findings were confirmed at surgery. Two distinct patterns of extracapsular spread were identified. The first pattern, noted in three cases, involved tumor extension along iliopsoas. The second pattern, noted in five cases, involved tumor extension along the obturator externus fat plane. In three cases both patterns were present.

CONCLUSIONS

Extra-articular spread of synovial osteochondromatosis is common. Patterns of extra-articular spread may be predictable based on involvement of recognized periarticular bursae of the hip joint. Bursal patterns of extra-articular spread include extension into the iliopsoas bursa as well as communication along the obturator externus bursa of the hip.