Rupture of a non-rheumatoid popliteal cyst: a syndrome mimicking thrombophlebitis.

Rupture of a popliteal cyst and dissection of its contents into the calf may produce pain, swelling, a positive Homan's sign and other findings closely resembling thrombophlebitis of the calf. The correct diagnosis is not often made, and the patient is subjected to needless long term anticoagulant therapy with its potential complications. To avoid this, it is essential that this possibility be kept in mind in all patients in whom the diagnosis of thrombophlebitis is considered. The history of preexisting arthritis of the knee, joint effusion and popliteal cyst are strongly suggestive of a ruptured popliteal cyst. This diagnosis can be verified by arthrography, ultrasonography, computed tomography and radionuclide scanning. Arthrography is preferred because it reveals superior anatomic detail thereby making differentiation between an encapsulated calf cyst, with smooth walls, and rupture, with irregular feathery margins, possible. Three illustrative cases are presented and the literature is reviewed.