A ganglion cyst is a fluid-filled sac that forms from synovial fluid found in a joint capsule or a tendon sheath. They are one of the most common benign soft-tissue masses. These cysts often occur around the wrist but can be seen on the foot as well. They are usually isolated, uniform in shape and range in size.
The exact cause of ganglion cysts is not known but they are thought to arise from trauma. This can result from either a single event or constant microtrauma to the area.
After thoroughly examining the mass, your doctor may shine a light through the mass to see if it illuminates or they may remove some fluid from the cyst to evaluate it. Your doctor will determine whether or not an x-ray or advanced imaging is also necessary.