The imaging spectrum of Baker's (Popliteal) cysts.

Baker's (Popliteal) cysts are frequently encountered on cross-sectional imaging of the knee. These consist of enlarged gastrocnemius semimembranosus bursa which typically communicate with the knee. They may be imaged with a variety of techniques including arthopgraphy, CT, ultrasound and MRI, with the latter two being more commonly used. Examples of bursa imaged with all of the above techniques are demonstrated in the essay, as well as variance of normal appearance and pathological entities including ruptured bursa, abnormally positioned bursa, osteochondromatosis, septic complications of the bursa and pigmented villonodular synovitis.