Primary synovial osteochondromatosis of a subdeltoid bursa

Primary synovial osteochondromatosis (SOC) is known to be intra-articular and wherever it is observed outside a synovial joint, it is associated with the involvement of the nearby joint. Primary SOC has not been reported to involve a subdeltoid bursa. We present a case of a 52-year-old woman having a large number of loose bodies in a large tumor in the subdeltoid bursa. The swelling was first noticed by the patient 2 years back. Plain roentgenogram revealed soft tissue swelling only with no areas of calcification. On MRI, multiple nonosseous loose bodies were visualized in the bursa deep to the deltoid muscle. A surgical excision of subdeltoid bursa was done. A biopsy confirmed it to be cartilaginous loose bodies in synovial lining sugestive of metaplastic transformation of the synovial tissue.