A ganglion cyst is a tumor or swelling on top of a joint or the covering of a tendon. It is a fluid filled sac which can be felt below the skin. The cause of these cysts is unknown although they may form in the presence of joint or tendon irritation or mechanical changes. It is also known as a wrist cyst, Bible cyst, or dorsal tendon cyst. It is usually attached to a tendon sheath in the hand or wrist or connected with an underlying joint; however, some have no obvious connection to any structures. It may be soft or hard, may or may not be painful, and may get bigger or smaller on its own. It looks like a sac of liquid (cyst). Inside the cyst is a thick, sticky, clear, colorless, jellylike material. Most commonly, ganglions are seen on the wrist (usually the back side) and fingers, but they can also develop around joints on the shoulder, elbow, knee, hip, ankle and foot. The ganglion cyst often resembles a water balloon on a stalk (see Figure 2), and is filled with clear fluid or gel.