A ganglion is a sac-like swelling or cyst formed from the tissue that lines a joint or tendon. The tissue, called synovium, normally functions to produce lubricating fluid for these areas. A ganglion is a cyst formed by the synovium that is filled with a thick jelly-like fluid. While ganglia can follow local trauma to the tendon or joint, they usually form for unknown reasons.
A ganglion can spontaneously rupture and go away. Other treatment options include removal of the ganglion fluid with a needle and syringe (aspiration) with or without an injection of cortisone medication. Occasionally, the entire ganglion is resected with surgery. Persons with a persisting or recurring ganglion should be evaluated for signs of systemic forms of arthritis.