Within the popliteal fossa there is a neurovascular bundle that contains the sciatic nerve (and its two divisions), the popliteal artery and the popliteal vein. There are also numerous small bursae associated with the posterior aspect of the knee joint and the muscles and tendons in this region. It is possible that this mass is arising from the posterior structures of the knee joint, which include synovial outpouchings, the menisci, and the muscles and tendons of this region.