LAUSR

OBJECTIVE To determine whether the morphologic features of the main pancreatic duct (MPD) of main-duct-involved-IPMN (i.e., Main duct or mixed main duct/side branch) have implications for risk of malignancy and extent of resection. BACKGROUND International consensus guidelines acknowledge the presence of various MPD morphologies (i.e., diffuse vs. segmental main-duct-involved-IPMN) without precise definition of each entity and with limited data to guide treatment strategy. METHODS All consecutive main-duct-involved-IPMN patients (2005-2019) with a MPD diameter ≥5 mm by cross-sectional imaging were reviewed from a prospective institutional database. Morphologic features of the MPD were correlated with the identification of high-grade dysplasia or adenocarcinoma (HGD/PDAC) by logistic regression modeling. In patients who underwent partial pancreatectomy, pre-operative MPD morphologic features were correlated with the future development of HGD/PDAC in the pancreatic remnant by Cox hazards modeling. RESULTS In a cohort of 214 main-duct-involved-IPMN patients, the overall rate of HGD/PDAC was 54.2%. MPD morphologic characteristics associated with HGD/PDAC included: maximal MPD diameter (5-10 mm: 29.8%; 10-14 mm: 59.0%; 15-19 mm: 78.6%; ≥20 mm: 95.8%; P<0.001), segmental extent of maximal dilation (<25%: 28.2%; 25-49%: 54.9%; 50-74%: 63.1%; ≥75%: 67.9%; P=0.002) and non-segmental MPD diameter (<5 mm: 21.5% vs. ≥5 mm: 78.5%, P<0.001). Diffuse MPD dilation involving ≥90% extent was rare (5.6%). After a median follow up of 50 months, 7 (7.2%) patients who underwent partial pancreatectomy for IPMN without associated PDAC developed HGD/PDAC in the pancreatic remnant. Maximal MPD diameter, segmental extent of maximal dilation, or non-segmental MPD diameter were not associated with the development of HGD/PDAC in the pancreatic remnant. However, a mural nodule on preoperative imaging was associated with the development of HGD/PDAC in the pancreatic remnant. CONCLUSIONS "Diffuse" involvement with homogenous dilation of the MPD was rare. For the majority of patients with segmental main-duct-involved-IPMN, the MPD morphology conferred malignancy risk. Duct morphology was not predictive for the development of high-grade dysplasia or invasive disease in the pancreatic remnant, implying the safety of limited pancreatic resection for initial surgical management.