Ganglion (GANG-lee-on) cysts are the most common type of soft tissue mass that form under your skin. Most commonly, ganglions are seen on the backside of the wrist and fingers, but they can also develop on your shoulder, elbow, and knee. Ganglions form when tissues surrounding certain joints become inflamed and swell up with lubricating fluid. In some cases, cysts can increase in size when the tissue is irritated and often can disappear spontaneously. Although these masses, which can be painful or painless, sometimes grow, they're not tumors or cancerous. The cause of ganglions is not always clear, however, conditions such as rheumatoid (rue-MAH-toyd) arthritis (arth-RYE-tis) have been associated with these cysts. Occupational factors can also play a role in the development of ganglions. Those occupations that require you to overuse certain joints, such as your wrist and fingers, pose a risk for developing ganglion cysts. A physician recognizes most ganglion cysts during physical examinations, but sometimes X-rays are used to confirm the diagnosis. A procedure called 'aspiration,' or the draining of the contents of the cyst, may be required to distinguish the differences from other causes of swelling. Other treatments for cysts can consist of rest or splinting the affected joint. If the cyst continues to reoccur, a surgeon can remove it.