Simple pancreatic cyst

Cystic

pancreatic lesions: MR imaging findings and management. Retention cyst. A small cyst is observed on T2w (a) and MRCP (b), without evidence of a mass. On a follow-up study two years later, a focal obstruction of the main pancreatic duct appeared with chronic obstructive pancreatitis features upstream (c, d), all findings of high suspicion of malignancy (pancreatic carcinoma on histology). (From: Morana G, Faccinetto A, Venturini S: Pancreas. In: Vanzulli A, Colagrande S, Grazioli L, Morana G (eds), MRI of the abdomen—technique and imaging findings. Poletto, Milan, 2021)

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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 . In contradistinction to other solid viscera, simple cysts in the pancreas are a rare entity .

Terminology

Several publications use the term simple cyst of the pancreas in a loose manner, 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 actually ever resected leaving their ultimate pathological nature unknown .

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

Commonest 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 . 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 characterization.

Risk factors

childhood
autosomal dominant polycystic kidney disease
autosomal recessive polycystic kidney disease
cystic fibrosis (includes pancreatic cystosis)
von Hippel-Lindau disease

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 hemorrhage, 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) . They are benign and do not show malignant transformation.

The etiology remains unknown, however their diagnosis predominantly in a pediatric 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 hemorrhage 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).

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.