Ganglions are fluid-filled cysts commonly found on the tendons and joints of the foot and ankle. They may develop suddenly or over time and appear as a small, raised lumps. While ganglions are usually benign and harmless, they may cause pain if the cyst puts pressure on nearby nerves, which may results in pain, weakness or numbness. They often occur spontaneously when the soft sheath around a tendon or joint swells and fills with fluid. 

You should still seek medical attention if you notice a lump on your foot or ankle. Treatment is not always necessary, but many wish to have the cyst removed for cosmetic reasons or to relieve pain that has developed over time. Ganglions can be treated through a variety of methods, depending on the size and severity of the cyst. Some of these treatments include removing the fluid from the cyst with a syringe or surgical excision if necessary.