Enhancing Mural Nodules in the Main Pancreatic Duct of Main and Mixed Types of Intraductal Papillary Mucinous Neoplasms: Does Size Matter in Malignancy Risk?

BACKGROUND/AIMS: Most guidelines recommend surgical resection of all main duct (MD) and mixed-type (MT) intraductal papillary mucinous neoplasms (IPMNs) in suitable patients. However, there is little evidence regarding the malignancy risk of enhancing mural nodules (EMNs) that are present only in the main pancreatic duct (MPD) in patients with MD- and MT-IPMNs. Therefore, this study aimed to identify the clinical and morphological features associated with malignancy in MD- and MT-IPMNs with EMNs only in the MPD. METHODS: We retrospectively enrolled 50 patients with MD- and MT-IPMNs with EMNs only in the MPD on contrast-enhanced magnetic resonance imaging. We evaluated the clinical characteristics and preoperative radiologic imaging results of MPD morphology and EMN size and analyzed the risk factors associated with malignancy. RESULTS: Histological findings of EMNs were low-grade dysplasia (38%), malignant lesions (62%), high-grade dysplasia (34%), and invasive carcinoma (28%). On the receiver operating characteristic curve, the cutoff value of EMN size on magnetic resonance imaging for best predicting malignancy was 5 mm (sensitivity, 93.5%; specificity, 52.6%; area under the curve, 0.753). Multivariate analysis showed that only EMN >5 mm (odds ratio, 27.69; confidence interval, 2.75 to 278.73; p=0.050) was an independent risk factor for malignancy. CONCLUSIONS: EMNs of >5 mm are associated with malignancy in patients with MD- and MT-IPMNs with EMNs that are present only in the MPD, in accordance with the international consensus guidelines.