What Are Mucous Cysts?
Mucous cysts are a type of small ganglion (fluid filled) cyst found near the end joint of a finger joint affected by osteoarthritis. The cyst is caused by a small bone spur that irritates the lining of the finger joint that causes an outpouching of this lining underneath the skin. They often start as a small firm bump, but may increase in size. As the cyst gets larger, it may rupture, leaking a clear fluid. There is usually little pain from the cysts themselves; however, discomfort can be from the underlying arthritis. In larger, long-standing cysts, the fingernail may develop a ridge deformity.
What are the Symptoms?
A mucous cyst usually appears as a small bump under the skin near the tip of the finger. If it develops near the nail bed, it may cause the fingernail to form a groove as the nail grows. Though mucous cysts are not usually painful, they may become irritated if they are frequently rubbed or bumped. The inflamed joint associated with the cyst may also cause discomfort. The skin covering the cyst may become thin, making it prone to rupturing and releasing a clear fluid. Because these cysts are directly connected to the joint, there is a severe risk of an infection of the joint if the ruptured cyst becomes contaminated.
What Causes Them?
Mucous cysts may be caused by arthritis or joint synovitis, both types of inflammation between the joints of the finger. A weakness in the tissue between joints can lead to the formation of a cyst. Though cysts typically develop slowly, they may appear rapidly depending on its underlying cause.
How Are Mucous Cysts Diagnosed?
The cyst is diagnosed by physical exam, as they have a typical appearance. X-rays may be used to evaluate the joint for arthritis and identify the offending bone spur. Advanced imaging is rarely needed.
How Are The Cysts Treated?
Most small cysts are treated with simple observation.
It is not recommended to “pop” the cyst at home as this may lead to an infection of the finger joint.
Proper aspiration, or draining of the cyst, may be performed in the office. Steroid injections may be used to reduce inflammation in the joint and surrounding tissue.
Surgical services are reserved for cysts that are larger in size and at risk for rupture due to the thinning of the overlying skin.
Surgical excision of the cyst and joint debridement is performed with a short outpatient procedure done under either local anesthesia or light sedation. It is important to remove the bone spur as well as the cyst to prevent recurrence. The finger is immobilized in a splint for approximately a week, after which the sutures are removed and return to normal activity follows over the next few weeks.