Cysts

Cysts: The pathological term ‘cyst’ means a swelling consisting of a collection of fluid in a sac which is lined by epithelium or endothelium.
True cysts : True cysts are lined by epithelium or endothelium. If infection supervenes, the true lining may be destroyed and replaced by granulation tissue. The fluid is usually serous or mucoid and varies from brown-staining by altered blood to almost colourless. In epidermoid, dermoid and branchial cysts the contents are like porridge or toothpaste, as a result of the shedding of desquamated cells. Cholesterol crystals are often found in the fluid of branchial cysts.
False cysts (pseudocysts) :Walled-off collections of fluid not lined by epithelium are not regarded as true cysts. A pseudocyst of th e pancreas is an encysted collection of pancreatic enzyme rich fluid lined by granulation tissue or fibrous tissue. Pancreatic pseudocysts are often in the retroperitoneum deep to but bulging into the lesser sac; they may occur anywhere in the abdominal cavity and even track into the mediastinum and pleural cavities. In tuberculous peritonitis, fluid may be walled off in cystic form by adherent coils of intestine. Fluid may collect in the centre of a tumour (cystic degeneration), due to haemorrhage or necrosis. This can also happen in the brain as a result of ischaemia, and an ‘apoplectic cyst’ is formed. In acute pancreatitis fluid collections loculated by viscera and fibrin are called ‘acute fluid collections’; these often occur in the lesser sac but are neither cysts nor pseudocysts as they are not lined by either epithelium, granulation tissue or fibrous tissue.
A classification of cysts
Congenital Sequestration dermoids , Tubuloembryonic (tubulodermoid), Cyst of embryonic remnants
Acquired Retentio, Distention, Exudation ,Cystic tumours, Implantation dermoid , Trauma
& Degenerati