Synovial chondromatosis presenting as painless soft tissue mass--a report of 19 cases.

Primary synovial chondromatosis is a disorder of joints, tendon sheaths and bursae characterized by the formation and growth of cartilaginous nodules. It usually presents clinically with joint symptoms and is frequently associated with intra-articular loose bodies. A large soft tissue mass is an unusual presentation which, both clinically and radiologically, raises the suspicion of malignancy. Nineteen cases of synovial chondromatosis presenting as soft tissue tumours were reviewed. They were all adjacent to joints but with no joint symptoms. Histology showed the typical features of benign synovial chondromatosis, including foci of cartilage cells showing cytological atypia. This is well recognized and does not indicate malignancy. Clinical follow up confirmed this with local recurrence only in three patients. It is important to be aware of this unusual presentation as the alternative diagnosis of a chondrosarcoma, as initially diagnosed in some of these cases, has major implications regarding the treatment of these patients.