Introduction
Pancreatic cysts are fluid-filled lesions found within the pancreas. The vast majority are benign and are found incidentally, however due to their risk of malignancy, need appropriate investigation and monitoring.
Pancreatic cysts are largely asymptomatic, however due to the increased use of cross-sectional imaging in recent years, their incidence is increasing, being identified incidentally on imaging. Current estimates place the prevalence of pancreatic cysts at around 8%.
Pancreatic cysts are different to pseudocysts, which are fluid filled regions that occur anywhere within or adjacent to the pancreas, however lack an epithelial-lined wall.
Figure 1 – The parts of the pancreas
Cyst Subtypes
Pancreatic cysts can be classified by secretions, by histology, or by risk of malignancy (high risk vs low risk).
Cysts are broadly classified into mucinous (lined with mucin-producing epithelium) or non-mucinous (namely simple cysts, pseudocysts, and serous cystadenomas). As a general rule, serous cysts are lower risk and mucinous cysts are higher risk.
Mucinous cysts include intraductal papillary mucinous neoplasms (IPMNs) and mucinous cystic neoplasms (MCNs)*, pancreatic neuroendocrine tumours with a cystic component, and pancreatic adenocarcinoma with cystic degeneration
*MCNs and IPMNs are differentiated by the presence of a connection to the pancreatic ductal system; MCNs do not communicate with the ductal system while IPMNs originate in the ducts
Clinical Features
In 70% of cases, pancreatic cysts are asymptomatic, found incidentally on imaging.
For symptomatic cysts, presenting complaints include non-specific abdominal pain or back pain (from mass effect and compression), post-obstructive jaundice, or vomiting.
High Risk Clinical Features
High-risk clinical features of pancreatic cysts include obstructive jaundice without alternative explanation, new onset diabetes mellitus, recurrent pancreatitis due to a pancreatic cyst, a substantially elevated serum CA19-9 level, or cytology suggesting the presence of high-grade dysplasia or neoplasia
Rarely, cysts can become infected and present with systemic features of infection. Those that undergo malignant transformation will present with features of metastatic disease (obstructive jaundice, weight loss)
In the majority of cases however, examination will likely be unremarkable; in rare occasions, there may be a tender abdomen, a palpable mass, or abdominal distension.
Figure 2 – Histology of a Benign Mucinous Cystic Neoplasm
Differential Diagnoses
The main two differentials for a pancreatic cyst are pancreatic pseudocysts and pancreatic cancer. Further investigation of pancreatic cysts is mainly to stratify the risk of potential malignancy.
Investigations
As suggested, most cases are identified incidentally on cross-sectional imaging. Current NICE guidelines suggest Pancreatic Protocol CT scan (Figure 3) or Magnetic Resonance CholangioPancreatography (MRCP) to further assess and evaluate pancreatic cysts.
Risk Stratification on Imaging
Imaging can be used to stratify those cysts that are low risk versus those that are high risk.
- Low risk features – cyst diameter <3cm, cystic morphology with central calcification, or asymptomatic
- High risk features – main pancreatic duct dilatation greater than 10mm, any enhancing solid component, or non-enhancing mural nodule
Based on the features identified on initial imaging, further investigation may be warranted, typically through Endoscopic US scan with Fine Needle Aspiration (EUS-FNA) for cytology and biomarker assessment (e.g. amylase). In those with concerning features, CA19-9 serum levels should also be checked
Figure 3 – Pancreatic cyst (arrow) on the pancreatic head seen on CT imaging
Management
Most pancreatic cysts will be discussed at the multidisciplinary team (MDT) meetings, to plan for any further imaging, follow-up, or surgical intervention warranted.
A combination of history, examination, radiological features, fluid cytology, and biomarker analysis frequently can diagnose the type of pancreatic cyst and determine the risk of malignant transformation.
Symptomatic cysts, cysts with high-risk features, and those with known high risk for malignancy (including main duct IPMNs and MCNs) should be referred for surgical resection.
Patients with cysts associated with malignancy (IPMNs, MCNs) who are surgical candidates but without high-risk features are recommended to undergo surveillance*. MRI pancreas is the recommended surveillance imaging modality; intervals between scans depends on the cyst, however often varies between 6 months to 2 years.
*Patients who are not surgical candidates due to advanced age or co-morbidities should not undergo surveillance
Prognosis
The prognosis of these patients is highly dependent on subtype of the cyst; non-malignant and non-invasive cysts will have excellent prognosis.
Key Points
- Pancreatic cysts are fluid-filled lesions found within the pancreas, usually asymptomatic
- Cysts are broadly classified into mucinous or serous cysts; serous cysts are often lower risk and mucinous cysts are higher risk
- Most pancreatic cysts are found incidentally and require formal characterisation with CT pancreas or MRCP imaging
- A combination of history, examination, radiological features, fluid cytology, and biomarker analysis frequently can diagnose the type of pancreatic cyst and determine the risk of malignant transformation
- Symptomatic cysts, cysts with high-risk features, and those with known high risk for malignancy should be referred for surgical resection, the remainder can undergo regular surveillance
