What Is a Ganglion Cyst?

A ganglion cyst is a common non-cancerous fluid-filled swelling that occurs around a joint or tendon, appearing as a small, firm “knot” that can move about under the skin. These fluid-filled sacs appear next to tendons and joints on the wrist and hand, and foot and ankle, but they can also occur on the knee and finger.

Ganglions are thought to develop from the synovium, the lining between tendons and joints, producing a fluid that lubricates the area during joint movements.