Prediction of malignancy in main-duct intraductal papillary mucinous neoplasm (MD-IPMN) based on radiologic features: How should we treat if main duct dilatation is under 10 mm?

Abstract

Surgical indications of main-duct intraductal papillary mucinous neoplasm (MD-IPMN) except for main pancreatic duct (MPD) diameter ≥ 10 mm remain controversial. Diameter of MPD alone could result in overestimation of malignancy. We aimed to predict malignancy risk of MD-IPMN based on morphologic features presented in CT scan or MRI. We retrospectively reviewed 258 patients with main-duct or mixed-type IPMN between 2000 and 2017 in our institute. MD-IPMN is defined as segmental or diffuse dilatation of MPD > 5 mm without other causes of obstruction. We divided MD-IPMN into focal ectatic and diffuse type by pattern of dilated MPD. Of 258 patients with main-duct involved IPMN, 47 (18.2%) and 211 (81.8%) had main-duct and mixed-type IPMN. Risk of malignant (high-grade dysplasia + invasive lesion) (66.0% vs. 46.9%; p = 0.018) and invasive IPMN (53.2% vs. 26.1%; p < 0.001) were higher in MD-IPMN than mixed-type. Patients with MPD ≥ 10 mm (n = 100) had more malignant (64.0% vs. 41.8%; p < 0.001) and invasive (43.0% vs. 23.4%; p < 0.001) lesion than those with MPD 5-9 mm (n = 158). Of 47 patients with MD-IPMN, focal ectatic and diffuse type were presented in 27 (57.4%), and 20 (42.6%). Forty three patients (91.5%) showed MPD ≥ 10 mm. Mean MPD diameter (maximal) was 17.4 ± 12.2 mm in MD-IPMN group. Diffuse type had more invasive carcinoma compared with focal ectatic type (70% vs. 40.7%; p = 0.047). Five-year survival was worse in diffuse type (85.0% vs. 52.1%; p = 0.011). Focal ectatic MD-IPMN and mixed-type IPMN did not significantly differ in risk of malignant (55.6% vs. 47.4%; p = 0.425) lesion and in 5-year survival (85.0% vs. 77.6%; p = 0.995). Symptoms (p = 0.011), CA19-9 > 37 IU/mL (p = 0.014), MPD ≥ 10 mm (p = 0.017), thickened cyst wall (p = 0.005), and distal atrophy (p = 0.015) were independent predictive factors for malignant IPMN. Malignancy risk increased proportionally to the diameter of MPD in MD-IPMN. Those with above mentioned risk factors should be the candidate of surgery.