MRI of cystic collection of the three joint

We present the main MR features of cystic lesions around the knee joint. Popliteal cysts are the most frequently seen. The usually result from extrusion of joint fluid into the gastrocnemio-semimembranosus bursa but they can have an atypical location or extension. They are most often due to a meniscal, ligamentous, degenerative or inflammatory joint disease responsible for a chronic joint effusion. Meniscal cysts are always associated with a horizontal tear. Medial meniscal cysts are larger and can extend far from the joint. Bursitis occur as a result of inflammation or infection of a bursa. Their location is stereotyped and they do not communicate with the knee joint. Ganglion cysts or ganglia are benign cystic lesions which can affect peri-articular tissues as well as subchondral bone or cruciate ligaments. MRI is now a simple and noninvasive way of obtaining etiologic diagnosis and guiding therapy. (authors)