Baker's cyst sonogram

This transverse sonogram of the popliteal region shows a Baker's cyst taking the form of an X-shaped cross of St. Andrew. The gastrocnemius bursa lying around the medial head of the gastrocnemius tendon (GC) is filled with fluid (asterisks), as is the bursa of the semimembranosus tendon (SM), which lies just superficial to the femoral bone (B).