Tenosynovial osteochondroma of the hand. A case report and brief review.

A 61-year-old man presented with a slowly growing, painless mass over the dorsum of his right hand. Roentgenography, computed tomography, and a radionuclide bone scan revealed a soft-tissue mass with mineralization but no bone or joint involvement. Routine laboratory tests and a chest roentgenogram were negative. A biopsy was inconclusive. The mass was removed en bloc and was diagnosed as synovial osteochondroma arising from the extensor tendon sheaths. The patient has been symptom-free 16 months postoperation. The literature indicates that these tumors occur almost exclusively in the hands or feet and are thought to develop by metaplasia from the mesenchymal cells of the synovial membrane; mineralization and ossification of the tumor are secondary. The actively growing tumor is often cellular and may show atypical cytologic features. Such microscopic characteristics should not be interpreted as evidence of a low-grade chondrosarcoma. A review of the literature failed to disclose a case with malignant transformation, although several lesions had recurred, some more than once. For this reason, complete removal of the involved synovia is of great importance.