Simple pancreatic cysts, also known as true epithelial cysts or retention cysts, are unilocular cysts within the pancreas, lined by a monolayer of epithelium, which lack communication with the pancreatic ducts 1,5. In contradistinction to other solid viscera, simple cysts in the pancreas are a rare entity 5.
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Terminology
Several publications use the term simple cyst of the pancreas loosely, as a catch-all term for small cysts in the pancreas which are indeterminate and often turn out to be benign; however, in these studies, very few of these lesions are ever resected leaving their ultimate pathological nature unknown 2,4.
The term true cyst is also used by some authors to refer to all cystic lesions other than pseudocysts, i.e. non-pseudocysts are real cysts.
Epidemiology
The most common cystic lesion in the pancreas is a pseudocyst. Most simple pancreatic cysts are seen in children.
In adults true simple pancreatic cysts are rare; mean age of diagnosis is 45 years, with a female predilection, and they are more likely in the tail of the pancreas 5. True prevalence of simple pancreatic cysts in adults is likely underestimated as many small cysts seen on modern cross-sectional imaging are only followed-up without any attempt at definitive pathological characterisation.
Pancreatic cystic lesions (PCLs) come in a variety of forms, with some types posing a greater risk of malignancy than others. PCLs can potentially develop into pancreatic ductal adenocarcinoma (PDAC).
Risk factors
childhood
cystic fibrosis (includes pancreatic cystosis)
Clinical presentation
Often asymptomatic unless very large and impinging on adjacent structures/organs.
Pathology
Simple pancreatic cysts are lined by a monolayer of cuboidal epithelium and contain simple fluid, without debris or haemorrhage, or superinfection. Indeed they are structurally identical to simple cysts in other viscera, e.g. renal. The fluid has few cells within it with mixed inflammatory cells. Analysis of the fluid demonstrates low levels of amylase, lipase and carcinoembryonic antigen (CEA) 5. They are benign and do not show malignant transformation.
The aetiology remains unknown, however their diagnosis predominantly in a paediatric population strongly suggests that they are congenital.
Radiographic features
Features on imaging are the same as uncomplicated simple cysts in other organs, e.g. renal. Therefore pure fluid-density contents with an imperceptible wall, no solid elements, septa or enhancement. No calcification or haemorrhage will be present. In addition the background appearance of the pancreas will be unremarkable, with no communication between the cyst and the pancreatic ducts (cf. pancreatic pseudocyst).
PCLs can be classified into two broad categories: nonmucinous (solid pseudopapillary neoplasms, cystic pancreatic neuroendocrine tumours, serous cystadenomas, pseudocysts, true epithelial cysts, and lymphoepithelial cysts) and mucinous cysts (intraductal papillary mucinous neoplasms).
Ultrasound/CT/MRI
Appearances as per simple cysts in other solid viscera. Evidence of background pancreatic pathology, e.g. pancreatitis, not usually present.
Treatment and prognosis
Simple cysts of the pancreas are benign and usually do not require active treatment, unless they are large and symptomatic.
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