Accessory muscles located in the region of the popliteal fossa are very rare. MRI scan performed in a 52-year-old man with right knee pain revealed an anomalous muscle in the region of the popliteal fossa. Considering the muscle originated from the medial side of the lateral head of the gastrocnemius muscle and attached to the posteromedial articular capsule of the knee joint, it is consistent with the accessory popliteus muscle, previously reported. To our best knowledge, MRI finding about the accessory popliteus muscle has been reported in only one case. We present a case of the accessory popliteus muscle incidentally identified on MRI.
