A ganglion cyst, also known as a synovial cyst, is a benign, fluid-filled cyst found in or around a joint. It is quite common and benign, but it can also be painful and disfiguring. When located inside a joint, a ganglion cyst can limit motion.
Ganglion cysts are usually diagnosed with the help of an ultrasound image. Some can be left alone. But if the cyst is causing pain or complications, it can be aspirated (drained) with a hypodermic needle or removed using arthroscopic surgery.