Ganglion cyst on the ankle of a 77 year old female patient that has spontaneously ruptured. This cyst (fluid-filled sac) is named for its similarity to ganglion nerve clusters. Its cause is unknown, but it may result from overuse of a specific joint, causing the degeneration of the surrounding fibrous tissue and the development of a fluid-filled cystic structure. The cysts are usually asymptomatic, but may be removed surgically for cosmetic reasons.