Ganglion cyst

A ganglion cyst is a fluid-filled bump associated with a joint or tendon sheath. It most often occurs at the back of the wrist, followed by the front of the wrist.

The cause is unknown. The underlying mechanism is believed to involve an outpouching of the synovial membrane. Diagnosis is typically based on examination. The ability to shine through the bump or any past decrease in size supports the diagnosis of the bump as a ganglion cyst. Ganglion cysts are usually obvious upon observation. Medical imaging may be considered on infrequent occasions to rule out another diagnosis.

Treatment is not necessary. Options for treatment include needle aspiration or surgery. About half the time, they resolve on their own. About three per 10,000 people newly develop ganglion of the wrist or hand a year.

Presentation
The average size of these cysts is 2 cm, but excised cysts of more than 5 cm have been reported. The size of the cyst may vary over time. Between 50 and 70% of all masses on the hand and wrist are ganglion cysts.

Wrist
They commonly are found near the wrist joint, especially at the scapholunate area.

Common wrist ganglions include:
 * dorsal wrist ganglion
 * volar wrist ganglion
 * extensor retinaculum ganglion
 * occult ganglion
 * intraosseous ganglion
 * mucous cyst

Foot
In a 2007 study of patients in Glasgow whose foot lumps were removed surgically, 39 of 101 cases were ganglion cysts. The study replicated earlier findings that no ganglion cysts were found on the sole or heel. The authors wrote, "Although lumps in these areas may be ganglia, the surgeon should probably consider other diagnoses in the first instance." The researchers noted a preponderance of occurrence among females (85%) and that 11 of the other cases had been misdiagnosed as ganglion cysts before surgery.

Ganglion cysts are not limited to the hands and feet. They may occur near the knee, commonly near the cruciate ligaments, but they may occur at the origins of the gastrocnemius tendon, and anteriorly on Hoffa's infrapatellar fat pad. At the shoulder, they typically occur at the acromioclavicular joint or along the biceps tendon.

Other
From their common origin at a joint or tendon, ganglion cysts may form in a wide range of locations. Rarely, intraosseous ganglion cysts occur, sometimes in combination with a cyst in the overlying soft tissue. Rare cases of intramuscular ganglion cysts in the gastrocnemius muscle of the calf have been reported. It is possible for a cyst to be considerably displaced from the joint. In one extreme case, a ganglion cyst was observed to propagate extensively via the conduit of the common peroneal nerve sheath to a location in the thigh; in such cases surgery to the proximal joint to remove the articular connection may remove the need for a riskier, more extensive surgery in the neural tissue of the thigh. The cysts may intrude into the spine, which may cause pain and dysesthesia in distant extremities.

Cystic adventitial disease, in which a cyst occurs within the popliteal artery near the knee, has been proposed recently to occur by an articular mechanism, with a conduit leading from the joint, similar to the development of ganglion cysts, that spreads within the peroneal nerve.

Cysts that were compressing one or more nerves and causing bone erosions have been reported to occur near the shoulder joint.

Causes
The most commonly accepted probable cause of ganglion cysts is the herniation hypothesis, by which they are thought to occur as an out-pouching or distention of a weakened portion of a joint capsule or tendon sheath. This description is based on the observations that the cysts occur close to tendons and joints. The microscopic anatomy of the cyst resembles that of tenosynovial tissue. The fluid is similar in composition to synovial fluid. Dye injected into the joint frequently ends up in the cyst. Dye injected into the cyst rarely enters the joint, however, which has been attributed to the apparent formation of an effective and one-way "check valve", allowing fluid out of the joint, but not back in.

In synovials, post-traumatic degeneration of connective tissue and inflammation have been considered as causes. Other possible mechanisms for the development of ganglion cysts include repeated mechanical stress, facet arthrosis, myxoid degeneration of periarticular fibrous tissues and liquefaction with chronic damage, increased production of hyaluronic acid by fibroblasts, and a proliferation of mesenchymal cells.

Diagnosis


Ganglion cysts are diagnosed easily, as they are visible and pliable to touch.

Ultrasonography (US) may be used to increase diagnostic confidence in clinically suspected lesions or to view smaller "occult" cysts as a cause of dorsal wrist pain with forceful extension.

Treatment
At least 33% resolve without treatment within six years, and 50% within 10 years.

Surgical excision is the primary discretionary, elective treatment option for ganglion cysts. Alternatively, a hypodermic needle may be used to drain the fluid from the cyst (via aspiration). The recurrence rate is about 50% following aspiration of a ganglion cyst.

Complications
Complications of treatment may include joint stiffness and scar formation. Recurrence of the lesion is more common following excision of a volar ganglion cyst in the wrist. Incomplete excision that fails to include the stalk or pedicle also may lead to recurrence, as will failing to execute a layered closure of the incision.

Prognosis
Recurrence rate is higher in aspirated cysts than in excised ones. Ganglion cysts have been found to recur following surgery in 12% to 41% of patients.

A six-year outcome study of the treatment of ganglion cysts on the dorsal wrist compared excision, aspiration, and no treatment. Neither excision nor aspiration provided long-term benefit better than no treatment. Of the untreated ganglion cysts, 58% resolved spontaneously; the postsurgery recurrence rate in this study was 39%. A similar study in 2003 of ganglion cysts occurring on the palmar surface of the wrist states: "At 2- and 5-year follow-up, regardless of treatment, no difference in symptoms was found, regardless of whether the palmar wrist ganglion was excised, aspirated, or left alone."

Etymology
Being a misnomer that has persisted into modern times, the ganglion cyst is unrelated to the neural "ganglion" or "ganglion cell"; its etymology traces back to the ancient Greek γάγγλιον, a "knot" or "swelling beneath the skin", which extends to the neural masses by analogy. Generally, Hippocrates is credited with the description of these cysts.

Bible cyst
The term "Bible cyst" (or "Bible bump") is derived from an urban legend or historical effort to hit the cyst with a Bible. Trying to treat the lesion by hitting it with a book, though, is discouraged.

A historical method of treatment for a ganglion cyst was to strike the lump with a large and heavy book, causing the cyst to rupture and drain into the surrounding tissues. Historically, a Bible was the largest or only book in any given household, and was employed for this treatment. This led to the nickname of "Bible bumps" or "Gideon's disease" for these cysts. This treatment risks injuring the person and thus is not recommended.