Clinicopathological Meaning of Size of Main‐Duct Dilatation in Intraductal Papillary Mucinous Neoplasm of Pancreas: Proposal of a Simplified Morphological Classification Based on the Investigation on the Size of Main Pancreatic Duct

Abstract

BACKGROUND: The 2012 consensus guideline on intraductal papillary mucinous neoplasm of the pancreas (IPMN) described a three-stage criteria involving main pancreatic duct (MPD) size with definitions of malignancy relevant for treatment decisions. Re-evaluation and simplification of this classification for clinicians are warranted. METHODS: Data from the Seoul National University Hospital of 375 consecutive patients with pathology-confirmed IPMN after surgery were analyzed. The association between clinicopathologic characteristics of IPMN and MPD size was assessed. The cut-off value of MPD size for a current definition of malignancy prediction was calculated. RESULTS: Diagnostic accuracy for malignancy was highest when the cut-off value of MPD size was 7 mm (area under the curve=0.7126). Dichotomizing IPMN into MPD≤7 mm versus MPD> mm, patient age (p=0.039), sex (p=0.001), presence of mural nodule (p<0.001), and invasiveness risk (13.2 vs. 39.8%, p<0.001) resulted in significantly different results. Mural nodule-negative patients with MPD>7 mm had a significantly lower 5-year survival rate than those with MPD≤7 mm (78.4 vs. 91.4%, p=0.006). Among patients with MPD size≤7 mm, elevated serum CA 19-9 and mural nodule were independent risk factors of malignancy. Patients with MPD size≤7 mm without these risk factors had malignancy risk of 2.6%. CONCLUSION: Using the definition of malignancy provided in the 2012 guideline, the MPD size> mm criterion was statistically driven. The current morphologic classification of IPMN can be simplified as branch-duct-predominant IPMN (MPD≤7 mm)' and main-duct-predominant IPMN (MPD> mm). Patients who are determined to have main-duct-predominant IPMN and branch-duct-predominant IPMN with elevated serum CA 19-9 or mural nodule are recommended to undergo surgical treatment.