Pseudocyst

1. An abnormal sac that resembles a cyst but has no membranous lining. Also called adventitious cyst, false cyst.
2. A cyst whose wall is formed by a host cell and not by a parasite.
3. A cyst consisting of a host cell enclosing a mass of Toxoplasma parasites, usually found in the brain.

An abnormal dilated space resembling a cyst but not lined with epithelium, e.g. a retroperitoneal accumulation of urine from a leaking ureter.

• pancreatic p. — accumulation of pancreatic secretions and cellular debris may occur with recurring episodes of pancreatitis, most commonly in dogs.
• perirenal p., perinephritic p. — see feline perirenal cysts.
• salivary p. — see salivary mucocele.

A chest CT scan revealing pulmonary contusions, pneumothorax, and pseudocysts

A pseudocyst is a pathological collection of fluid. A pseudocyst may appear to be a true cyst to the naked eye or on a CAT scan. However, it is technically not a cyst. The wall of a true cyst consists of a clearly defined epithelial cell layer. The wall of a pseudocyst consists of granulation and/or fibrous tissue (which is present secondary to inflammation).

A pancreatic pseudocyst results from the passage of inflammatory fluid into the omental bursa. This is typically a complication of acute pancreatitis, but may also occur following abdominal trauma.

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