Mural nodule of 10 mm or larger as predictor of malignancy for intraductal papillary mucinous neoplasm of the pancreas: Pathological and radiological evaluations

Background: We had previously reported that mural nodule (MN) >= 10 mm was optimal predictor of malignancy for intraductal papillary mucinous neoplasm (IPMN). However, little is known about its microscopic findings and imaging detectability. Methods: Medical records and resected specimens of consecutive patients with IPMNs harboring MN >= 10 mm were reviewed. Imaging detectability was determined on reports basis. Malignant IPMNs (noninvasive + invasive carcinomas) were microscopically classified according to localization of high-grade dysplasia (HGD) within MN. Results: Thirty-six patients were included. Imaging detectability of MN >= 10 mm in CT, MRI, US and EUS were 64%, 68%, 89%, and 97%, respectively. Thirty-three (92%) IPMNs were histologically diagnosed as malignant. Thirty percent of malignant IPMNs were classified into "diffuse HGD within MN", 40% into "focal HGD within MN", and 30% into "HGD outside MN", in which HGD was not located within MN but in low papillary epithelia around MN. Overall sensitivity of pancreatic juice cytology was calculated as 58%, and for "diffuse HGD within MN", "focal HGD within MN", and "HGD outside MN" as 80%, 62%, and 30%, respectively (p = 0.0237). Univariate-analysis showed localization of HGD within MN was associated with true positive cytology (OR = 5.33, p = 0.043). Conclusions: Detectability of MN >= 10 mm is excellent in US and EUS. Although HGD is observed within MN in 70% of malignant IPMNs, HGD is located only in low papillary epithelia around MN in the remaining 30%, in which sensitivity of pancreatic juice cytology is shown to be inadequate. (C) 2015 IAP and EPC. Published by Elsevier B.V. All rights reserved.