Pediatric Popliteal Cyst

• Etiology: Fluid-filled synovial-lined lesion in popliteal fossa between medial head of gastrocnemius tendon and semimembranosus tendon via communication with knee joint
• Imaging US:
  — Well-defined cyst which may or may not contain debris with a neck at its deepest extent that extends into joint space between the semimembranosus tendon and medial head of gastrocnemius tendon
  — Identification of the neck is necessary to make a definitive diagnosis
• DDX: Large parameniscal cyst, liquefying hematoma
• Complications: Dissection of cyst, rupture of cyst, compression of popliteal vessels and tibial nerve by cyst, compartment syndrome
• Treatment: Most resolve spontaneously
• Clinical:
  — Often incidental finding
  — May present acutely with rupture or chronically as popliteal fossa mass

Radiology Cases of Popliteal Cyst