A mucous cyst is a fluid-filled sac that occurs on the finger joint closest to the nail. The fluid is clear, thick, sticky, similar to mucous. The cyst may thin the skin and may cause a groove to form in the nail. Most patients who develop a mucous cyst have wear and tear arthritis (osteoarthritis) of the involved joint. The cyst has a stalk that is connected to the joint. It is thought that underlying bone spurs from the arthritis weakens the joint lining allowing the cyst to form.
How is a mucous cyst diagnosed?
The mucous cyst typically has a characteristic appearance, and the diagnosis is straight-forward for most hand specialists. Radiographs are usually ordered to confirm underlying arthritis of the joint and associated bone spurs (also known as osteophytes).
Does the mucous cyst need to be treated?
Most mucous cysts are not painful. If they are not causing pain or hand dysfunction, they do not require treatment. In these cases, observation for changes in the cyst is all that is needed. Some cysts can go away on their own. If a patient develops pain, recurrent drainage, or nail deformity, surgery may be recommended. Even if not painful, diagnosis should be confirmed by a physician, as other diseases may mimic a mucous cyst or ganglion cyst. These cysts should not be drained at home with a needle because a serious infection in the joint can occur. See images below for examples:
Images from Dr John Erickson