Acral synovial chondrosarcoma.

Acral chondrosarcoma is rare. Synovial chondrosarcoma is even rarer. Synovial chondrosarcoma arising without evidence of pre-existing or concurrent synovial chondromatosis is exceedingly rare. We present a case of acral synovial chondrosarcoma involving both sides of the metacarpophalangeal joint of the thumb in a 69-year-old man. Radiographically, the lesion mimicked gout. On MR imaging, the lobulated contours of the soft tissue mass suggested synovial chondromatosis. Histological examination revealed a chondrosarcoma, which on the basis of imaging findings we present as having arisen from the synovium. The tumor invaded a portion of the cartilage of the metacarpophalangeal joint and equally destroyed the bones of the distal metacarpal and base of the proximal phalanx of the thumb, while sparing the bony joint surfaces.