A Baker's (popliteal synovial) cyst may present with findings suspicious for deep vein thrombosis involving the lower leg, especially if the cyst leaks or ruptures. Recognition of the condition allows for early initiation of appropriate therapy and prevents an unnecessary evaluation for deep vein thrombosis.


Origin of the cyst: gastrocnemius-semimembranous bursa


Clinical features that may be confused with thrombophlebitis:

(1) swelling or palpable mass of the calf

(2) pain and tenderness in the calf

(3) positive Homan's sign

(4) may be bilateral


Characteristic findings:

(1) A Baker's cyst most often occurs a patient with a chronic knee disorder causing an effusion within the joint (inflammatory, degenerative, neuropathic arthropathy, especially rheumatoid or osteoarthritis; previous surgery or trauma), but may occur in patients without such a history.

(2) Symptoms referred to the pain, including a feeling of fullness, a swelling, and/or posterior knee pain.

(3) With rupture of the cyst, there may be ecchymosis over the foot, ankle, lower leg and/or popliteal fossa.

(4) The workup for thrombosis will usually be negative (venography or Doppler ultrasonography; negative D-dimer test).


NOTE: A patient may have both superficial/deep vein thrombosis and a ruptured Baker's cyst involving the same leg.


Diagnostic tests:

(1) venous duplex scan: excludes venous thrombosis and can demonstrate the cyst

(2) ultrasound: demonstrates cystic nature (anechoic)

(3) MRI: demonstrates fluid leakage into soft tissue

(4) arthrography: radiographs after injection of contrast material into the joint space


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