Synovial Fibroma in the Knee: a case report

Intraarticular synovial fibroma is extremely rare with only 14 known cases reported in the literatures. Descriptions and illustrations about the imaging features are also limited. We hereby present a case of synovial fibroma in the knee joint which shares similar imaging features and clinical presentations with localized pigmented villonodular synovitis (PVNS). Therefore, it is important that synovial fibroma be included in the list of differential diagnosis through the process of reaching a definitive diagnosis of PVNS. Correspondence Author to: Meng-Yuan Tsai Department of Radiology, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan No. 386, Da-Zhong 1st Road, Zuo-Ying, Kaohsiung 813, Taiwan J Radiol Sci 2013; 38: 21-25 Intraarticular synovial fibroma 22 J Radiol Sci March 2013 Vol.38 No.1 The histopathological examination (Fig. 4) showed well-circumscribed fibrous nodules separated by clefts. The tumor was composed of spindled fibroblasts embedded in a collagenous stroma with cellular regions, areas of relative cellular paucity, and foci consisting of myxoid change. Mitosis was scarce, and the tumor cells tested positive immunohistochemically for smooth muscle actin (SMA) and negative for S-100 and CD34. The histological diagnosis of a synovial fibroma (fibroma of the tendon sheath) was thus reached.