A case of idiopathic bursal synovial chondromatosis resembling rheumatoid arthritis.

Primary synovial osteochondromatosis is an unusual condition, which generally involves otherwise normal joints. Joints commonly affected in descending order of frequency are knee, hip, glenohumeral joint, elbow and ankle, though any articulation may be involved. Synovial osteochondromatosis has been also encountered in tendon sheaths and periarticular bursa. We report a case with the clinical findings, radiographic features, surgical and histological data of primary subacromial-subdeltoid bursa synovitis. X-ray radiographs of the right glenohumeral joint as well as CT and MRI of the right shoulder zone were performed. A soft tissue mass around the lateral margin of the proximal humerus without evidence of any calcification/ossification or erosion of the adjacent cortex was detected on both X-Rays and CT images. Multiple nodules of almost equal size appeared that were isointense on T1-weighted spin-echo images and slightly hyperintense on T2 weighted spin-echo images compared with the signal intensity of the surrounding skeletal muscles. The main differential diagnosis was pigmented villonodular synovitis, rheumatoid arthritis with rice bodies and secondary synovial osteochondromatosis. Based on the results of all modalities the diagnosis of primary synovial chondromatosis of subdeltoid/ subacromial bursa was concluded.