Solitary Extraarticular Synovial Chondromatosis; Radiologic-Pathologic Correlation.

Synovial chondromatosis (SC) is a locally aggressive neoplasm consisting of multiple hyaline cartilaginous nodules. This neoplasm typically manifests as multiple intra-articular calcified or uncalcified nodules, whereas the extraarticular form is particularly rare. We herein present a case of solitary extraarticular SC arising in the hand and correlate the imaging findings with pathologic findings. A male patient in his 60s presented with a progressively enlarging mass in his left hand over a period of three years. Radiograph showed a lobulated calcified mass adjacent to the first metacarpal bone. Computed tomography (CT) revealed ring and arc calcification, indicating cartilaginous lesion. No continuity with bone was observed. In magnetic resonance imaging (MRI), the signal of the mass was heterogeneous low to high intensity on both T1- and T2-weighted images. High intensity reflecting fat on T1-weighted image and marked high intensity reflecting cartilage on fat-suppressed T2-weighted image were shown in the mass. After gadolinium administration, the enhancement of the mass was faint. An en bloc excision of the mass was performed, and the tumor was histologically diagnosed as extraarticular SC. Microscopically, the tumor consisted of fibrous tissue, mature fat tissue, and lobules of cartilage. Extraarticular SC should be taken into consideration when cases of lobulated soft tissue mass with ring and arc calcification and a fat component (T1 hyperintense) in the hand are encountered.