A ganglion is a fluid-filled cyst that develops under the skin near a joint or tendon—most commonly on the wrist or back of the hand, but sometimes on the foot.
Ganglia are not harmful and may be present for years without causing problems, although some cause pain or restrict movement.
If they cause no symptoms, they can be left to disappear by themselves. If they cause pain or impede movement, they can be drained or removed surgically