A ganglion is a sac-like swelling or cyst. The tissue that lines a joint or tendon produces a substance called synovial fluid, which acts to lubricate movement. Ganglia are fluid-filled cysts formed by this tissue. They may appear around almost any joint, but most frequently in the wrist and ankle. They are usually pea-sized, but can sometimes develop to the size of a small tomato.
It’s best to think of a ganglion like the inner tube of a bicycle wheel poking out of the tyre.
What causes a ganglion?
An injury to a joint or tendon can cause a ganglion, but often they form for unknown reasons. They are usually painless, and often not visible.
What is the treatment?
A ganglion can suddenly disappear on its own, sometimes as a result of pressure or trauma (traditionally, a ganglion was treated by hitting it with the family bible). If it is causing pain, or is unsightly, it can be aspirated (removal of the fluid by syringe), but it may recur. Sometimes a steroid injection is given at the same time. Surgical removal under anaesthetic is another possibility.
Ganglions are never dangerous and are not a health risk.