A ganglion cyst is a fluid-filled swelling that develops near...

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.
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.
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.
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.
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.