Main Duct Thresholds for Malignancy Are Different in Intraductal Papillary Mucinous Neoplasms of the Pancreatic Head and Body-Tail

Background & Aims: The risk of malignancy is uncertain for intraductal papillary mucinous neoplasms (IPMNs) with main pancreatic duct (MPD) of 5-9 mm. No study has correlated MPD size and malignancy considering the anatomic site of the gland (head versus body-tail). Our aim was to analyze the significance of MPD in pancreatic head/body-tail as a predictor of malignancy in main-duct/mixed IPMNs. Methods: Retrospective analysis of resected patients between 2009-2018 was performed. Malignancy was defined as high-grade dysplasia and invasive carcinoma. MPD diameter was measured with magnetic resonance imaging. Receiver operating characteristic curve (ROC) analysis was utilized to identify optimal MPD cut-off for malignancy. Independent predictors of malignancy were searched. Results: Malignancy was detected in 74% of 312 identified patients. 213 patients (68.3%) had IPMNs of the pancreatic head and 99 (31.7%) of the body-tail. ROC analysis identified 9 and 7 mm as the optimal MPD cut-offs for malignancy in IPMNs of head and body-tail of the pancreas, respectively. Multivariate analysis confirmed that MPD ≥9 mm (pancreatic head) and ≥7 mm (body-tail) were independent predictors of malignancy along with macroscopic solid components, positive cytology and elevated CA 19-9. The risk of malignancy was low for IPMNs with MPD ≤8 mm (pancreatic head) or ≤6 mm (pancreatic body-tail) unless high-risk stigmata or multiple worrisome features were present. Conclusions: Different thresholds of MPD dilation are associated with malignancy in IPMNs of the head and body-tail of the pancreas. The risk of malignancy for IPMNs with MPD ≤8 mm (pancreatic head) or ≤6 mm (pancreatic body-tail) lacking high-risk stigmata or multiple worrisome features is low.