• Klaus Sahora, Carlos Fernández-del Castillo, Fei Dong, Giovanni Marchegiani, Sarah P Thayer, Cristina R Ferrone, Dushyant V Sahani, William R Brugge, Andrew L Warshaw, Keith D Lillemoe, and Mari Mino-Kenudson.
• Department of Surgery, Massachusetts General Hospital, Boston, MA; Department of Surgery, Harvard Medical School, Boston, MA.
• Surgery. 2014 Sep 1;156(3):611-21.

BackgroundThe malignant potential of intraductal mucinous neoplasm of the pancreas (IPMN) is associated closely with main pancreatic duct (MPD) involvement. Because mixed-type IPMN is thought to have the same malignant potential as that of main-duct (MD)-IPMN, resection is recommended; however, the biological nature of mixed-type IPMN with only minimal involvement of MPD (min-mix-IPMN) may be different.MethodsA prospective database of 404 resected IPMNs was re-reviewed to subclassify mixed-type IPMNs. We defined min-mix-IPMN as absence of gross abnormalities (except for dilatation) of MPD and noncircumferential microscopic involvement of MPD limited to few sections.ResultsWe identified 46 min-mix-IPMNs, 163 IPMNs with extensive involvement of MPD (ex-mix-IPMN), 175 branch-duct (BD)-IPMNs, and 20 MD-IPMNs. The majority of min-mix-IPMNs were found incidentally and increased cyst size on surveillance was the leading operative indication. The median diameter of MPD was 2 mm in min-mix-IPMN versus 9 mm in ex-mix-IPMN (P < .0001), and cysts ≥10 mm were present in 62% of ex-mix-IPMNs versus 93% of min-mix-IPMNs (P < .0001). Most importantly, the vast majority of min-mix-IPMNs exhibited gastric-type epithelium, similar to BD-IPMNs, whereas intestinal-type epithelium was present in half of ex-mix-IPMNs, similar to MD-IPMNs. The prevalence of high-grade lesions was less in min-mix-IPMN than ex-mix-IPMN (P < .0001). These differences were reflected in better disease-specific outcomes of min-mix-IPMN compared with ex-mix-IPMN (P = .046).ConclusionMin-mix-IPMN often presents with no MPD dilation and is an incidental finding by microscopic examination. min-mix-IPMN shares the pathologic features and less aggressive biology with BD-IPMN. We propose that min-mix-IPMN be categorized differently than ex-mix-IPMN.Copyright © 2014 Mosby, Inc. All rights reserved.

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