This is a benign soft tissue mass filled with clear, thick fluid that can appear anywhere in the body and comes in various sizes. Since the foot and ankle have very little fat, cysts in this area can cause irritation, nerve pinching, or discomfort with walking and wearing shoes. Often times, they are not bothersome and can be left alone whereas in some situations treatment is necessary.
The cause of a ganglion cyst is not well known but some theorize trauma or some compromise within a joint capsule or tendon sheath causing it to bulge outwards.
Conservative approaches include shoe modification or giving it time to go away on its own. It had once been popular to take a Bible and hit it to make it go away (“Bible therapy”) but this is no longer recommended. If it persists, a qualified doctor can provide steroid injections which may help it shrink. Aspiration (withdrawing fluid) can also help deflate it but often times it will come back.
Surgery is definitive treatment to remove the ganglion cyst. Recurrence with surgery is much less than with conservative approach.