Cause
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.
According to a 2011 paper, "The pathogenesis of the ganglion cysts is controversial. Herniation of the synovium into the surrounding tissue like 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."
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