A ganglion is a benign, fluid filled mass (cyst) that forms and firmly attaches itself to an underlying joint or tendon. The exact cause of ganglions is unknown. One theory is that ganglions form after trauma to the tissue layer, which produces the synovial fluid that lubricates the adjacent joint or tendon. The cyst forms when the fluid accumulates outside the joint or tendon.
Although cosmetically unpleasant, most ganglions need no medical intervention, often disappearing on their own. But some ganglions are painful, pressing on nerves or limiting movement in adjacent joints.
Aspiration of the cyst to withdraw the fluid minimizes the symptoms but carries a 50% rate of reoccurrence. The most reliable course of treatment is surgical removal. Surgery involves removing the cyst and excising a portion of the attending tendon or joint. The reoccurrence rate after surgical intervention drops to 10%.