Incidental Pancreatic Duct Dilatation on Ct and Mri: Prevalence and Risk of Malignancy

Background: Incidental main pancreatic duct (MPD) dilatation creates a diagnostic dilemma because physiological ageing, inflammatory obstruction, intraductal neoplasia, and occult pancreatic cancer can produce overlapping appearances. Published malignancy estimates vary substantially with referral setting and outcome definition. Objective: To critically examine prevalence, determinants of duct calibre, imaging predictors of malignancy, and the roles of magnetic resonance cholangiopancreatography (MRCP), endoscopic ultrasound (EUS), and surveillance. Methods: A targeted PubMed-based narrative review evaluated population studies, CT/MRI morphology cohorts, EUS investigations, longitudinal surveillance studies, and pancreatic neoplasm guidelines available through October 20, 2026. Findings were interpreted according to study population, measurement threshold, diagnostic selection, and whether outcomes represented invasive cancer, high-grade dysplasia, or any neoplasm. Results: A population-based MRI cohort reported MPD dilatation ≥5 mm in 81/2,985 individuals (2.7%); pancreatic cancer was diagnosed during follow-up in 2/81 participants with dilatation versus 24/2,904 without it. Selected cohorts with isolated dilatation or abrupt cutoff reported substantially higher diagnostic yields, which cannot be extrapolated to unselected incidental findings. Abrupt termination, focal parenchymal abnormalities, suspicious enhancement or diffusion restriction, associated biliary obstruction, and intraductal nodules are more informative than diameter alone. Age-adjusted MRCP reference limits reduce overclassification. In non-jaundiced incidental double-duct sign, a meta-analysis found an EUS-detected periampullary tumour yield of 5%, including adenomas and carcinomas. Conclusions: Incidental MPD dilatation warrants contextual assessment. Dedicated pancreatic imaging and selective EUS can identify occult causes, while surveillance should reflect residual suspicion and the underlying diagnosis. Neither surgical-series malignancy rates nor IPMN-specific thresholds should be applied indiscriminately to all dilated ducts.