Swelling forms under the skin and is attached to a tendon sheath or joint. These lumps are filled with the same thick, jellylike fluid that lubricates the joints. They can be hard or soft and small or large.
If you have such a lump, see your physician to make sure it is a ganglion cyst. Usually the cyst goes go away on its own, and watching and waiting is the first course of treatment.
Your physician may recommend that you wear a wrist brace or splint to relieve symptoms and allow the ganglion to decrease in size. Exercises may also be prescribed to strengthen the wrist and improve range of motion. If the cyst does not clear up over time and becomes painful or uncomfortable, it can be drained. Reccurent cysts may be surgically removed if necessary.
Unfortunately, theres no known way to prevent them.