Tenosynovial Giant Cell Tumor of the Pes Anserine Bursa with Bone Marrow Extension into the Tibia: A Case Report

Abstract

Tenosynovial giant cell tumor (TSGCT) is classified as a benign fibrohistiocytic tumor according to the World Health Organization (WHO) system of classification of bone and soft-tissue tumors. The proposed causes and pathogenesis include inflammation, trauma, toxin, allergy, and clonal chromosomal abnormalities (1). Jaffe et al. (2) described this condition as pigmented villonodular proliferative lesions arising from the synovium, bursa, or joint. Based on the growth characteristics of TSGCT, it can be divided into two forms: localized type and diffuse type. Localized-type TSGCT encompasses giant cell tumors of the tendon sheath and localized pigmented villonodular synovitis (PVNS), whereas diffuse types include conventional PVNS and diffuse giant cell tumors (3). TSGCT rarely involves the bursa, and only a few exceptional cases of TSGCT arising from the pes anserine bursa have been reported (4). In TSGCT, bone erosion is not an uncommon associated finding, especially in tumors of the tendon sheath of the finger or toe or in the joint space. However, only one previous case of associated bone erosion in TSGCT of the pes anserine bursa has been reported (5). Herein, we report an exceptional case of TSGCT of the pes anserine bursa with bone marrow extension on magnetic resonance imaging (MRI). This case report was approved by the Institutional Review Board of our hospital, and the requirement for obtaining informed consent was waived.