Popliteal cysts may be formed by the escape of a synovial effusion into one of the popliteal bursae. There is usually preexisting knee joint pathology. Presenting complaints include pain and swelling in the posterior aspect of the knee. The cyst may dissect into the calf between the muscle planes and produce pressure on draining lymphatics and veins, resulting in lower leg edema. These cysts are often mistakenly treated as deep vein thrombosis.