Masses in the extensor mechanism of the knee: an unusual presentation of gout.

Tophaceous gout presenting as a soft tissue mass in an unusual location can pose a diagnostic challenge for radiologists. Tophi sometimes occur in a variety of unusual anatomic locations making them difficult to distinguish from tumors such as sarcomas. We report two cases of gout in the extensor mechanism of the knee, with imaging findings that were initially concerning for a neoplasm. One mass occurred in the patellar tendon and the other mass involved the quadriceps tendon. Both lesions had enigmatic imaging findings and to arrive at a definitive diagnosis, incisional biopsies were performed.