A ganglion is a fluid-filled swelling of the lining of a joint or tendon. Although ganglions can form on any part of the foot, they most often appear on the ankle or top of the foot.
Ganglions tend to change in size, and are usually slow-growing.
People who wear boots are more vulnerable to ganglions, as this type of footwear puts stress on the foot and ankle. However, if the ganglion puts pressure on the nerves in the overlying skin, it can cause tingling, numbness, or pain. Ganglions sometimes swell, and their size can change with different activities or a change in weather. Because ganglions are sometimes mistaken for tumors, it is important to have a complete examination, and tests to confirm the diagnosis. Usually you can see through a ganglion but not through a tumor.