A cyst is an abnormal fluid-filled structure which is lined by epithelium; with one exception: lung cysts contain gas, not 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:
- Von Hippel-Lindau
- autosomal dominant polycystic kidney disease
- polycystic liver disease
- cystic lung disease
History and etymology
Cyst is derived from the Ancient Greek word 'κυστις' (kystis) 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.