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
