Cyst

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Cyst, in medicine, encapsulated sac, having no opening, and enclosing liquid or semisolid pathological or foreign material. The cyst wall, formed of fibrous connective tissue or of muscular fibers, has an inner surface lined with epithelium.

Retention cysts arising from distension of preexisting spaces result from the closure of a duct such as that of a sebaceous gland. An effusion of blood into a body cavity may result in an exudation cyst. Dermoid cysts are due to faulty development during the embryonic period. Adventitious cysts develop around foreign bodies or parasites introduced into deep tissue. When an inert body such as a metal or glass splinter is embedded in muscle tissue, it may become encysted. Another type of adventitious cyst is formed by the larvae of certain parasitic worms. Treatment of cysts is by surgical removal of the entire sac.

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