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|Classification and external resources|
Cyst on dorsum of left hand
|This article may be too technical for most readers to understand. (March 2014)|
|Classification and external resources|
Cyst on dorsum of left hand
A ganglion cyst or synovial cyst  or myxoid cyst, also known as Gideon's Disease, a Bible Cyst or Bible Bump, is a non-neoplastic soft tissue lump that may occur in any joint, but most often occurs on or around joints and tendons in the hands or feet. It is caused by leakage of fluid from the joint into the surrounding tissue.
The average size of these cysts is 2.0 cm, but cysts of more than 5 cm have to be excised. The size of the cyst may vary over time, and can increase after activity.
It is most frequently located around the dorsum of the wrist and on the fingers. A common site of occurrence is along the extensor carpi radialis brevis as it passes over the dorsum of the wrist joint. Although most commonly found in the wrist, ganglion cysts may also occur in the foot.
Ganglion cysts are "commonly observed in association with the joints and tendons of the appendicular skeleton, with 88% "in communication with the multiple small joints of the hand and wrist" and 11% with those of the foot and ankle."  They are most often found around the wrist joint, especially at the scapho-lunate area, which accounts for 80% of all ganglion cysts.
In a 2007 study of patients whose foot lumps were being surgically removed in Glasgow, 39 of 101 cases were ganglion cysts. The study replicated an earlier result that no ganglion cysts were found on the sole or heel of the foot; the authors wrote that "Although lumps in these areas may be ganglia, the surgeon should probably consider other diagnoses in the first instance." They also noted a marked female preponderance (85%) and that 11 of the other cases had been misdiagnosed as ganglion cysts before surgery.
Ganglion cysts can also occur about the knee, commonly near the cruciate ligaments, also 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.
From their common origin at the joint or tendon, ganglion cysts can form in a wide range of locations. Rarely, intraosseous ganglion cysts occur, sometimes in combination with a cyst in the overlying soft tissue. Very rare cases of intramuscular ganglion cysts in the gastrocnemius muscle have been reported. It is possible for the cyst to be displaced considerably from its connection to 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 can remove the need for a riskier, more extensive surgery in the neural tissue of the thigh. The cysts can even intrude into the spine, which can cause pain and dysesthesia in distant extremities.
It has recently been proposed that cystic adventitial disease, in which a cyst occurs within the popliteal artery near the knee, may occur by an articular mechanism, with a conduit leading from the joint, similar to the development of ganglion cysts that spread within the peroneal nerve.
Cysts have also been reported to occur nearby to shoulder joint, compressing one or more nerves and causing bone erosions.
The most commonly accepted cause of ganglion cysts is the "herniation hypothesis", in which they occur as "an out-pouching or distention of a weakened portion of a joint capsule or tendon sheath." This is based on the observations that the cysts occur close to tendons and joints, the microscopic anatomy of the cyst resembles that of the tenosynovial tissue, the fluid is similar in composition to synovial fluid, and dye injected into the joint capsule frequently ends up in the cyst, which can become enlarged after activity. However, dye injected into the cyst rarely enters the joint, which has been attributed to the formation of an effective "check valve" allowing fluid out of the joint, but not back in. Synovial cysts, posttraumatic degeneration of connective tissue and inflammation have been considered as the 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. Ganglion cyst can develop independently from a joint.
Ganglion cysts are easily diagnosed, as they are visible and pliable to touch.
Radiographs in AP and lateral views are obtained to exclude any more serious underlying pathology. Ultrasonography (US) may be done to increase diagnostic confidence in clinically suspected lesions or depict occult cysts. Intratendinous ganglia are readily distinguished from extratendinous ganglia during dynamic US. Microscopically, ganglionic cysts are thin-walled cysts containing clear, mucinous fluid.
Surgical treatments remain the primary option, other than doing nothing at all, for the treatment of ganglion cysts. The progression of ganglion surgery worldwide is to arthroscopic or mini-open wide awake excision of ganglion cysts. Alternatively, a hypodermic needle may be used to drain the fluid from the cyst (aspiration) and a corticosteroid is injected after cyst is empty. However, if the fluid has become thick owing to the passage of time, this treatment is not always effective.
One method for a ganglion cyst is to strike the lump with a large 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 commonly used; this led to the nickname of "Bible bumps" or "Gideon's disease."
Complications of treatment include stiffness in hand and scar formation.
A six-year outcome study of treatment of ganglia on the back (dorsum) of the wrist compared excision, aspiration and no treatment. Neither excision nor aspiration provided long-term benefit better than no treatment. Of the untreated ganglia, 58% resolved spontaneously; the post-surgery recurrence rate in this study was 39%. A similar study in 2003 of palmar wrist ganglion 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."
An apparent misnomer, 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. Hippocrates is generally credited with their description.
The term "Bible cyst" (or "Bible bump") is derived from a common treatment in the past that consisted of hitting the cyst with a Bible or similarly large book. Striking the ganglion cyst with a large tome is usually sufficient to rupture the cyst, and re-accumulation is uncommon.[inconsistent]
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