Extra-Articular Localized Tenosynovial Giant Cell Tumor of the Deep Infrapatellar Bursa

Tenosynovial giant cell tumor (TGCT), previously called pigmented villonodular tenosynovitis (PUNS) or giant cell tumor of tendon sheath, is a rare mesenchymal neoplasm arising from the synovium of joints and tendon sheaths. This condition has insidious and nonspecific symptoms making its diagnosis challenging. In most cases, localized tenosynovial giant cell tumors are described in the hand and are infrequent in larger joints. In the rare cases that affect the knee, the most common location is Hoffa's fat pad, followed by the suprapatellar bursa and the posterior capsule. Here, we describe a case of a histopathologically proven TGCT of the knee, found in an unusual location in the deep infrapatellar bursa, which was diagnosed by magnetic resonance imaging.