Invasive intraductal papillary mucinous neoplasms of the pancreas: relationships between mural nodules detected on thin-section contrast-enhanced MDCT and invasive components

Purpose To elucidate the relationships between mural nodules (MNs) and invasive components in patients with invasive intraductal papillary mucinous neoplasm (IPMN) on the basis of thin-section contrast-enhanced multidetector CT (CE-MDCT) and pathologic findings. Methods This retrospective study included 28 patients with surgically confirmed invasive IPMN. Two radiologists independently evaluated the thin-section (1-mm section thickness, no overlap) triple-phase CE-MDCT images for MNs, invasive components, and the continuity between them using a five-point scale (confidence scores of 1–3 as negative, 4 and 5 as positive). Kappa statistic was used to evaluate interobserver agreement. The CE-MDCT findings were correlated with pathologic findings. Results Interobserver agreement was good or excellent. MNs consisting of tumor cells were recognized in 12 (42.9%) of 28 patients with no discrepancy between the two radiologists. Invasive components were detected in 85.7% and 82.1% in the pancreatic parenchymal phase for radiologist 1 and 2, respectively, and recognized as hypoattenuating areas. Pathologic continuities between MNs and invasive components were confirmed in five (41.7%) of 12 patients with MNs and these were detected on CE-MDCT. When combined seven patients without continuities between MNs and invasive components and 16 patients without MNs, the invasive components pathologically derived from non-nodular low-height papillary epithelium in 23 (82.1%) of 28 patients. Conclusions The invasive components derived more often from low-height papillary epithelium without MN appearance on CE-MDCT than from MN. Careful attention should be paid to the existence of an invasive component even in the absence of an enhancing MN.