I recently wrote an article on mucous cysts for the Journal of Hand Surgery. These are a very common cause of finger masses. Mucous cysts are actually ganglion cysts of the small joint of the finger closest to the tip.
Much like ganglion cysts around the wrist (please see my last blog for more information on these), I initially treat mucous cysts by aspirating the fluid inside them. Please don’t try this yourself. The cyst connects to the underlying joint, and if an infection occurs it can spread to the underlying joint, causing a serious problem. Injecting steroids has not been shown to increase the cure rate, and may predispose to an infection.
Unfortunately, 30-70% (approximately half) of the mucous cysts return following aspiration. As these are just hernations of joint fluid, usually from an arthritic joint, they are benign and can often be observed without further treatment.
However, if pain persists or the skin starts to thin, it is very reasonable to have the cyst surgically excised. Thinned skin may make the underlying joint more susceptible to infection. If the skin thins enough, a local flap (soft tissue rearrangement) may become necessary. Many people don’t like the way the cyst looks and desire to have them removed. In addition, the cysts can cause a nail deformity. Removing the cyst can improve or resolve the nail deformity in 60-100%, depending on how long it has been present.
In order to permanently remove the cyst, the underlying joint must be addressed. Many dermatologists and non-hand surgeons often just try to just cut out the cyst or freeze it. That doesn’t usually work too well and recurrences are common follow these inadequate techniques. As for wrist ganglions, the balloon around the joint (the joint capsule) must have a section removed to prevent reformation of the one-way valve that causes these cysts in the first place (please see previous blog). In addition, the bone spurs must often be partially removed to allow a larger open space to prevent rescarring of the tissues around the joint with the recreation of a one-way valve and a recurrence of the cyst. The surgery should be performed by a fellowship-trained hand surgeon, as injury to the tendons, ligaments, and/or nail bed about the joint, with resultant deformity, may occur when surgery in this area is performed by those less well-versed in the anatomy and techniques of hand surgery.
The surgery can be performed under local anesthesia. The dressing can be removed after one week and most activities resumed, including getting the wound wet. However, the finger should not be submerged under water for two weeks. Patients should be aware that at least part of the pain my be due to the underlying joint arthritis, and that removing the cyst won’t cure that part of the pain.
If the skin is very thinned, a flap may be required to provide adequate soft tissue coverage over the joint. This requires rearranging some of the skin and underlying fat on top of the finger, but can also be performed under local anesthesia. Fortunately, this works very well and doesn’t slow down rehabilitation very much.