Bilateral tenosynovial giant cell tumor of the knee accompanied by chronic ACL tear

Tenosynovial giant cell tumors, also known as giant cell tumors of the tendon sheath (GCTTS), are a benign soft tissue tumor arising from the synovial tissue of the joint, tendon sheath, or mucosal bursa, or fibrous tissue adjacent to the tendon. Whereas GCTTS can arise in any synovial sheath, they are predominantly found in hand tendon sheaths and rarely in larger joints such as the knee or ankle [1,2]. The rare occurrence in larger joints, combined with a lack of characteristic symptoms, means GCTTS in the knee usually goes unsuspected in clinical diagnosis. Bilateral development of GCTTS is very rare [3]. To our knowledge, this is the first report to describe a case of bilateral intraarticular GCTTS arising from the anterior cruciate ligament (ACL) in both knee joints. The lesions were encountered during reconstruction of the ruptured ACLs.