Differentiating large-duct pancreatic ductal adenocarcinoma from malignant intraductal papillary mucinous neoplasm: MRI characteristics and diagnostic implications

• Differentiation between LD-PDAC and malignant IPMN is challenging on MRI. • Solid-dominant tumor morphology and peripancreatic infiltration favor LD-PDAC. • Cyst-dominant morphology and disproportionate duct dilatation favor malignant IPMN. • LD-PDAC has poorer survival vs IPMN, but similar to IPMN with associated cancer. • Nevertheless, substantial imaging overlap leads to a meaningful misdiagnosis rate. Differentiation between LD-PDAC and malignant IPMN is challenging on MRI. Solid-dominant tumor morphology and peripancreatic infiltration favor LD-PDAC. Cyst-dominant morphology and disproportionate duct dilatation favor malignant IPMN. LD-PDAC has poorer survival vs IPMN, but similar to IPMN with associated cancer. Nevertheless, substantial imaging overlap leads to a meaningful misdiagnosis rate. To evaluate magnetic resonance imaging (MRI) characteristics that differentiate large-duct pancreatic ductal adenocarcinoma (LD-PDAC) from malignant intraductal papillary mucinous neoplasm (IPMN). We retrospectively analyzed preoperative MRI data from 42 LD-PDAC patients, 201 malignant IPMN patients (166 with high-grade dysplasia and 35 with invasive carcinoma), and 8 LD-PDAC arising from IPMN patients. Two radiologists independently assessed MRI features including tumor morphology and accompanying imaging features. Multivariable logistic regression, diagnostic performance of combined imaging predictors, and survival outcomes across disease entities were evaluated. LD-PDAC predominantly appeared as solid-dominant tumors, either solid masses with internal cystic portions (69.0%) or pure solid masses (16.7%). Malignant IPMN presented mainly as cyst-dominant tumors, either pure cystic masses (55.2%) or cystic masses with internal solid components (42.8%). Multivariable logistic regression analysis identified solid-dominant tumor morphology (odds ratio [OR], 77.89; 95% confidence interval [CI], 4.94–1229.16), peripancreatic infiltration (OR, 34.47; 95% CI, 2.49–476.79), and absence of disproportionate pancreatic duct dilatation (OR, 0.06; 95% CI, 0.01–0.59) as independent imaging features favoring LD-PDAC. LD-PDAC showed significantly shorter overall and recurrence-free survival than malignant IPMN (p < 0.001), while survival did not differ significantly between LD-PDAC and IPMN with associated invasive carcinoma. Overall, 26.2% of LD-PDAC cases were misdiagnosed, mainly due to misinterpretation of cyst wall characteristics and atypical duct dilatation. MRI may aid in differentiating LD-PDAC from malignant IPMN by integrating tumor morphology and accompanying imaging features, including pancreatic ductal dilatation patterns and peripancreatic infiltration; however, substantial imaging overlap persists, resulting in a clinically meaningful misdiagnosis rate.