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Objective: Main pancreatic duct (MPD) involvement is a well-demonstrated risk factor for malignancy in intraductal papillary mucinous neoplasm (IPMN). Preoperative radiographic determination of IPMN type (main, mixed, or branch) is relied upon heavily in preoperative oncologic risk stratification. We hypothesize that preoperative radiographic assessment of MPD involvement in IPMN is an accurate predictor of pathologic MPD involvement.

Methods: Data regarding all patients undergoing resection for IPMN at a single, academic institution between 1992 and 2012 were gathered prospectively. Retrospective analysis of imaging, clinical, and pathologic data was undertaken. Preoperative classification of IPMN type was based on cross-sectional imaging (CT or MRI).

Results: Three-hundred and sixty four patients underwent resection for IPMN. Of these, 335 had adequate data on both radiographic and pathologic parameters for comparison. Of 184 suspected branch duct (BD) IPMN, 35 (19%) demonstrated MPD involvement on final pathology. Of 84 mixed-type (MT) IPMN 16 (19%) demonstrated no MPD involvement. Of 68 suspected main duct (MD) IPMN 13 (19%) demonstrated no MPD involvement. Of 35 of 184 (19%) that had a suspected BD IPMN but were found to have MPD involvement on pathology, 12 (34%) had invasive carcinoma. Alternatively, in patients with suspected MD or MT IPMN who ultimately were found to have no main duct involvement on pathology 2 (7%) demonstrated invasive carcinoma.

Conclusion: In resected IPMN, MPD involvement has been demonstrated as an independent risk factor for invasive cancer. Preoperative radiographic IPMN type correlates with final pathology in 81% of patients. In addition, risk of invasive carcinoma correlates with pathologic presence (or absence) of main duct involvement. Consequently, preoperative imaging for oncologic risk stratification may over or under weigh risk in up to one in five patients.