Treatment Choice - Treatment Choice | Compare Prices | Find Hospital | A ganglion cyst is a fluid-filled swelling that develops near a joint or a tendon. The cyst can range from the size of a pea to the size of a golf ball.<br/>Ganglion cysts look and feel like a smooth, soft lump under the skin. They are made up of a thick, jelly-like fluid, called synovial fluid, which surrounds joints and tendons to lubricate and cushion them during movement.<br/>Ganglions can occur alongside any joint in the body, but are most common on the wrist (particularly the back of the wrist), hand and fingers.<br/>Ganglions are generally harmless, but they can sometimes be painful, especially if they are next to a nerve. If they do not cause any pain or discomfort, they can be left alone and may disappear without treatment, although this can take a number of years.<br/>It is not clear why ganglions form, but they may be related to ageing or injury to the joint or tendon. They occur when the synovial fluid that surrounds a joint or tendon leaks out and collects beneath the skin.