Leaking Baker's cyst detected by magnetic resonance imaging.

Popliteal or Baker's cysts, often found incidentally during examination of the knee, are common. The authors report the magnetic resonance imaging (MRI) manifestations of a leaking Baker's cyst that initially presented as thrombophlebitis in a patient who had undergone reconstruction of the anterior cruciate ligament 4 months before; no cyst was present at the time of the surgery. Marked inflammatory changes apparent in the surrounding muscle and subcutaneous tissues were best appreciated in T2-weighted and fat-suppressed inversion recovery images. Although the results of ultrasonography suggested the diagnosis, they were not conclusive; MRI was a useful noninvasive adjunct in making the definitive diagnosis.