Cyst
This article discusses cysts as cavities in the body. For cysts as living things, see: Cyst (biology)
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A cyst (ancient Greek κύστις kýstis, German 'bladder') is a cavity in the tissue of the body lined by an epithelial membrane. If this closed tissue pocket is not surrounded by an epithelial membrane, but only by a connective tissue membrane, it is called a pseudocyst.
The cavity of a cyst can be filled with air (lung cysts), tissue fluid, urine (kidney cysts), blood, pus (empyema), mucus (in cystic fibrosis), sebum (atheroma), pus/sebum (pustule) or parasites (parasite cysts).
Origin
Cysts can be congenital or acquired. If the cyst is based on an outflow obstruction, it is called a retention cyst.
Congenital cysts arise from embryonic maldifferentiation, such as cystic kidney, cystic lung. In these cases, the respective organ always has a large number of cysts (polycysts).
Acquired cysts are caused by injuries, infections or parasite infestations. In these cases, the respective organ usually has only one or a few cysts. However, extensive parasite infestation can also lead to a large number of cysts (see: polycystic echinococcosis).
Distance
The surgical removal of a cyst is called a cystectomy, although this term is also used in medicine for the removal of the urinary bladder, even though this is an organ and not a cyst in the above sense.
