Synovial chondromatosis simulating neoplastic degeneration of osteochondroma: findings on MRI and CT.

A case is presented of synovial chondromatosis within a bursal sac overlying an osteochondroma in a patient with osteochondromatosis. This condition presented with a symptomatic soft tissue mass containing calcified bodies. It can be mistaken clinically and radiographically for malignant degeneration of an osteochondroma with development of chondrosarcoma. Magnetic resonance findings have not previously been described in this entity and proved helpful in the preoperative diagnosis. Magnetic resonance imaging was also helpful in defining the extent of the lesion. Ultrasound and other imaging modalities are also discussed, including the pathologic basis for the radiographic findings.