A ganglion cyst is a bump or mass that forms under the skin. Ganglions are most often seen on the back of the wrist and fingers, but can also develop on the shoulder, elbow, and knee. Ganglions form when tissues surrounding certain joints become inflamed and fill with fluid. Although they may appear to grow, they are not tumors or cancerous. They often disappear spontaneously.
The causes of ganglions are not always clear, but occupational factors play a role. Those occupations which require workers to overuse certain joints pose a risk for ganglion cysts.