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Popliteal cyst, also called Baker cyst, is a synovial fluid-filled distention of a bursa in the . It can be idiopathic or associated with underlying conditions, e.g., meniscal tear or osteoarthritis. Popliteal cysts are often discovered incidentally on imaging or physical examination but can also cause posterior knee pain and/or limit knee flexion. Large or ruptured cysts can cause calf swelling and may mimic the signs and symptoms of DVT. The diagnosis is usually clinical, but ultrasound is often used to exclude DVT and confirm the diagnosis. X-ray and/or MRI can be obtained to assess for underlying joint disease. Management of symptomatic cysts typically involves a trial of nonsurgical measures, e.g., pain management with NSAIDs and cyst drainage. Surgical resection may be considered for complications such as neurovascular compression or for persistent symptomatic cysts.
- Inflammation of the synovium stimulates excessive production of synovial fluid. 
- Risk factors: inflammatory, degenerative, or traumatic intraarticular changes in the knee joint (e.g., rheumatoid arthritis, osteoarthritis, meniscal lesions)
- Idiopathic (primary popliteal cysts) : most common in children
Popliteal cysts are typically asymptomatic and found incidentally on physical examination or imaging. 
- Possible symptoms
- Ruptured popliteal cyst: : leakage of synovial fluid into the calf muscles
- Clinical evaluation 
- Imaging: to rule out other causes of posterior knee pain or lower limb swelling (e.g., DVT) 
- Asymptomatic cysts: Treatment is not required in most cases. 
Symptomatic cysts 
- Nonsurgical management: preferred for at least 6 weeks if there are no neurovascular complications 
- Surgical resection: for persistent symptoms and/or neurovascular compression
- Ruptured popliteal cyst: conservative treatment, e.g., pain relief, rest, elevation
- Popliteal cyst rupture: can cause compartment syndrome in rare cases
- Pseudothrombophlebitis syndrome: caused by a large or ruptured popliteal cyst
- Cyst infection
- Neurovascular compression: e.g., tibial nerve injury, DVT due to venous compression
We list the most important complications. The selection is not exhaustive.