Ganglion cysts are benign, hard lumps of tissue that contain fluid and typically develop along the tendons of the ankle or foot. They can get bigger over time, but some do shrink and disappear spontaneously. Ganglion cysts that do not resolve on their own tend to cause significant discomfort and require treatment. Causes And Symptoms Ganglion cysts can occur when there's no apparent reason, but common causes of this type of cyst include trauma, overuse and joint stress, which can happen if you engage in high-impact exercise.