In adults it is usually related to synovial fluid buildup due to disorder or injury, such as inflammatory arthritis, osteoarthritis, or meniscus cartilage tear. May present with or without pain and discomfort, a feeling of tightness or stiffness, and swelling or mass, especially when standing or during hyperflexion of the knee. Uncommonly, dissection, rupture, and compression can occur with complications such as entrapped nerves, compartment syndrome, and ischemia requiring immediate care.
A primary popliteal cyst in a child may originate around the knee joint and adjacent bursa, is usually asymptomatic, and resolves on its own. A secondary popliteal cyst in a child is related to underlying knee joint pathology such as juvenile idiopathic arthritis or Lyme disease.
Management focuses on the underlying joint pathology and can include arthrocentesis, glucocorticoid injection, and inflammation control. For severe cases, procedures to aspirate the excess fluid and surgical excision may be employed.
M71.20 – Synovial cyst of popliteal space [Baker], unspecified knee
82675004 – Synovial cyst of popliteal space