Pancreatic Cystic Neoplasms

A heterogeneous group of cystic pancreatic lesions ranging from entirely benign to those with substantial malignant potential, increasingly detected incidentally on cross-sectional imaging performed for unrelated reasons. The central clinical task is stratifying risk of malignancy to decide between surveillance and resection.

Classification

• Intraductal papillary mucinous neoplasm (IPMN): mucin-producing tumour arising from the main pancreatic duct (main duct type, highest malignant potential, roughly 60-70% harbouring malignancy) or side branches (branch duct type, lower risk, roughly 15-20%), or mixed type. Communicates with the ductal system, which is key to diagnosis.
• Mucinous cystic neoplasm (MCN): occurs almost exclusively in women, typically in the body/tail, characterised by ovarian-type stroma on histology, does not communicate with the duct, has malignant potential related to size.
• Serous cystadenoma: benign, microcystic "honeycomb" or macrocystic architecture, central scar with calcification in a minority, negligible malignant potential, more common in older women.
• Solid pseudopapillary neoplasm: low-grade malignant potential, occurs in young women, well-circumscribed with solid and cystic/haemorrhagic components.
• Cystic degeneration of a solid pancreatic neuroendocrine tumour or of pancreatic adenocarcinoma, which must be distinguished from the primary cystic lesions above.
• Pseudocyst: not a neoplasm but the commonest cystic pancreatic lesion overall, following pancreatitis (acute or chronic), lacking an epithelial lining.

• Overwhelmingly asymptomatic and incidental, found on CT or MRI done for another indication.
• Abdominal pain, pancreatitis (from ductal obstruction by mucin in IPMN), jaundice (head lesions), or a palpable mass in larger or symptomatic lesions.
• New-onset or worsening diabetes and unexplained weight loss are worrying features that raise suspicion of malignant transformation.
• Pseudocyst: history of preceding pancreatitis, persistent abdominal pain, early satiety from mass effect, occasionally infection or haemorrhage into the cyst.

• Cross-sectional imaging (contrast CT or, preferably, MRI/MRCP for ductal detail) characterises location, size, septations, mural nodules, ductal communication and duct dilation.
• Worrisome features and high-risk stigmata (for IPMN, guiding management): high-risk stigmata include obstructive jaundice with a cystic lesion in the pancreatic head, an enhancing mural nodule of 5mm or more, and main pancreatic duct diameter of 10mm or more --- these mandate resection. Worrisome features (cyst 3cm or more, thickened/enhancing cyst wall, main duct 5-9mm, abrupt duct caliber change with distal atrophy, lymphadenopathy, rapid growth rate, elevated CA 19-9) warrant endoscopic ultrasound evaluation.
• Endoscopic ultrasound with fine needle aspiration: cyst fluid analysis for CEA (elevated in mucinous lesions), amylase (very high in pseudocyst and in lesions communicating with the duct, low in serous cystadenoma and solid pseudopapillary neoplasm), cytology, and increasingly molecular analysis (KRAS/GNAS mutations support IPMN).
• Serum CA 19-9, of limited standalone value but incorporated into risk assessment.
• Distinguish pseudocyst by clinical context (preceding pancreatitis) and absence of epithelial lining/septations/solid components on imaging.

• Surveillance imaging (MRI/MRCP or endoscopic ultrasound) at intervals determined by size and risk features for branch duct IPMN and MCN without high-risk stigmata, typically every 6-12 months initially, potentially extending if stable over years, though surveillance is generally lifelong given persistent malignant potential.
• Surgical resection (distal pancreatectomy or Whipple procedure depending on location) is indicated for: main duct or mixed IPMN, branch duct IPMN with high-risk stigmata or worrisome features on EUS assessment (mural nodule, positive cytology), MCN above 4cm or with mural nodules/symptoms, solid pseudopapillary neoplasm (all should be resected given malignant potential), and any cystic lesion with a confirmed or strongly suspected neuroendocrine or adenocarcinoma component.
• Serous cystadenoma: observation is generally appropriate even for large lesions given essentially negligible malignant potential; resection reserved for symptomatic or diagnostically uncertain lesions.
• Pseudocyst: many resolve spontaneously; intervention (endoscopic transmural drainage, typically EUS-guided cystgastrostomy, or percutaneous drainage) reserved for symptomatic, infected, enlarging, or complicated pseudocysts (haemorrhage, rupture), generally after allowing the wall to mature (4-6 weeks) unless infected or causing acute complications.
• Patient counselling on the lifelong nature of surveillance and the cumulative but generally low annual risk of malignant transformation in low-risk lesions, balanced against surgical morbidity of pancreatic resection.
• Multidisciplinary team discussion for borderline cases given the significant morbidity of pancreatic surgery weighed against malignant potential.