The lumps associated with ganglion cysts can be characterized by:

• Location. Ganglion cysts most commonly develop along the tendons or joints of your wrists or hands. The next most common locations are the ankles and feet. These cysts can occur near other joints as well.
• Shape and size. Ganglion cysts are round or oval and usually measure less than an inch (2.5 centimeters) in diameter. Some are so small that they can't be felt. The size of a cyst can fluctuate, often getting larger when you use that joint for repetitive motions.
• Pain. Ganglion cysts usually are painless. But if a cyst presses on a nerve — even if the cyst is too small to form a noticeable lump — it can cause pain, tingling, numbness or muscle weakness.

No one knows exactly what causes a ganglion cyst to develop. It grows out of a joint or the lining of a tendon, looking like a tiny water balloon on a stalk, and seems to occur when the tissue that surrounds a joint or a tendon bulges out of place. Inside the cyst is a thick lubricating fluid similar to that found in joints or around tendons.

Factors that may increase your risk of ganglion cysts include:

• Your sex and age. Ganglion cysts can develop in anyone, but they most commonly occur in women between the ages of 20 and 40.
• Osteoarthritis. People who have wear-and-tear arthritis in the finger joints closest to their fingernails are at higher risk of developing ganglion cysts near those joints.
• Joint or tendon injury. Joints or tendons that have been injured in the past are more likely to develop ganglion cysts.