Lipoma arborescens of the peroneal tendon sheath

Lipoma arborescens or synovial lipomatosis is a rare disorder characterized by mature fat infiltration of hypertrophic synovial villi, most frequently affecting the suprapatellar pouch of the knee. Involvement of the synovial tendon sheath is extremely rare with only a few reported cases in the literature. We present a case of lipoma arborescens involving the peroneal and flexor tendons sheaths of the ankle, review the few reported cases to date, and discuss MR imaging features of this rare entity.