Last revised by Daniel J Bell on 29 Oct 2019

A cyst is an abnormal fluid-filled structure which is lined by epithelium; with one exception: lung cysts may contain gas or fluid. By contradistinction, a pseudocyst lacks an epithelial lining and instead has a vascular and fibrotic capsule.

Cysts are extremely common and found in most organs. Examples include:

Multiple cysts can also be encountered as part of underlying genetic syndromes such as:

History and etymology

Cyst is derived from the Ancient Greek word 'κυστις' (kustis) meaning bladder. This etymology explains why some terms, e.g. cystitis, refer specifically to the urinary bladder, rather than inflammation of a cyst per se.

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