Ruptured popliteal cyst diagnosed by ultrasound before evaluation for deep vein thrombosis.

Most popliteal cysts are asymptomatic. However, cysts may rupture, resulting in pain and swelling of the leg that could also arise from other diseases, including deep vein thrombosis, lymphedema, cellulitis, and tear of a muscle or tendon. Therefore, it is difficult to diagnose a ruptured popliteal cyst based on only a patient's history and physical examination. Musculoskeletal ultrasound has been regarded as a diagnostic tool for ruptured popliteal cyst. Here, we describe a patient who was rapidly diagnosed as ruptured popliteal cyst by ultrasonography. Therefore, ultrasound could be used to distinguish a ruptured popliteal cyst from other diseases in patients with painful swollen legs before evaluation for deep vein thrombosis.