A ganglion is a small sac, or cyst, filled with a clear fluid that is like jelly. A ganglion may look like a bump on the hand or wrist. It also can appear on your feet, ankles, knees, or shoulders. It is not cancer. A ganglion can grow out of the protective area, or capsule, around a joint. It also can grow on a tendon sheath, which covers the ropelike tendons that connect muscle to bone. A ganglion may hurt or cause numbness if it presses on a nerve.
Many ganglions do not need treatment, and they often go away on their own. But if a ganglion hurts, becomes larger, causes numbness, or limits your activity, your doctor may want to drain it with a needle and syringe or remove it with minor surgery.