Understanding intraductal papillary mucinous neoplasm from pathogenesis to risk assessment: a pictorial review based on the kyoto guidelines.

Intraductal papillary mucinous neoplasm (IPMN) is the most common cystic neoplasm of the pancreas, encompassing a spectrum from benign to malignant lesions. Recently, the international guidelines for IPMN management were revised as the Kyoto guidelines, emphasizing the critical role of imaging in diagnosis, risk assessment, and surveillance. This article provides a comprehensive review of IPMN based on the updated guidelines, focusing on imaging-related aspects while elucidating the underlying pathological background. We present the three interrelated classification systems for IPMN: anatomical location (branch-duct, main-duct, or mixed type), histological subtype (gastric, intestinal, or pancreatobiliary), and degree of dysplasia (low-grade, high-grade, or associated invasive carcinoma). Understanding these classifications and their correlations is fundamental for imaging-based risk assessment and clinical decision-making. We discuss the two distinct carcinogenesis patterns in IPMN-sequential pattern resulting in high-grade dysplasia or invasive carcinoma associated with IPMN, and concomitant pattern leading to pancreatic ductal adenocarcinoma in IPMN-harboring pancreas. The article reviews high-risk stigmata and worrisome features that guide risk stratification, providing illustrative examples and highlighting potential diagnostic pitfalls. We also examine differential diagnoses including serous cystic neoplasm, mucinous cystic neoplasm, pancreatic intraepithelial neoplasia, pseudocysts, and large duct type pancreatic ductal adenocarcinoma. Finally, we review the current management algorithm and surveillance methods recommended by the Kyoto guidelines. This review aims to enhance radiologists' and clinicians' understanding of IPMN by integrating pathological knowledge with imaging findings, emphasizing that while high-risk stigmata are strong predictors of high-grade dysplasia or invasive carcinoma, surgical decisions should be individualized considering multiple factors including patient preferences, comorbidities, and life expectancy.