Intraductal papillary mucinous neoplasm of the pancreas : a study with magnetic resonance imaging

Intraductal papillary mucinous neoplasm (IPMN) of the pancreas is a cystic tumor that has the potential of malignant transformation. In this thesis, our aims were to investigate the natural course of IPMN disease and possible causes that may associate with IPMN disease or its severity. Additionally, we examined whether a shorter and thus more cost-effective imaging protocol could be used in IPMN surveillance without losing any of its diagnostic value. First, we studied the natural course of side-branch IPMN disease by evaluating patient images and medical records from 521 patients who visited the Helsinki University Hospital pancreatic outpatient clinic between 2014 and 2016. Every patient´s first and last surveillance images were evaluated retrospectively. A total of 377 side-branch IPMN patients were identified and classified into the following groups: presence or absence of worrisome features (WF) or high-risk stigmata (HRS) at the beginning of surveillance, the appearance of WF or HRS during surveillance, elevated or normal level of carbohydrate antigen 19-9 (CA 19-9), and stable or growing cysts that are under 15 mm. At the beginning of surveillance, 50% of patients had an under 15-mm primary cyst, of which 40% did not grow during surveillance. High-grade dysplasias or carcinomas did not exist in patients with normal CA 19-9 levels during surveillance. In conclusion, patients having side-branch IPMN cysts smaller than 15 mm that do not increase in size under surveillance and have no WF or HRS can be surveilled less frequently in the future. Second, we examined whether a shorter magnetic resonance imaging (MRI) protocol—the so-called ultrashort-protocol (USP) MRI—could be used for IPMN surveillance. Retrospectively, 183 IPMN patients that visited the Helsinki University Hospital pancreatic outpatient clinic between April 2015 and December 2016 were collected in this study. A total of 112 patients were included in the study. Two radiologists compared two imaging sets (USP versus long-protocol [S-LP]) per every patient separately, measuring the largest cyst and the main pancreatic duct (MPD) diameters and evaluating the presence or absence of MPD or cystic mural nodules and solid pancreatic tumors. Cyst or MPD nodules detection coincided in 95% and 99% of cases, WF or HRS detection in 92%, and solid pancreatic tumors in 99%. In conclusion, an ultrashort-protocol MRI provides nearly identical information compared to the longer protocols. Last, we studied if anatomical ductal variations have any association with IPMN disease. We retrospectively collected 108 IPMN patients and 106 subjects with healthy pancreas for the control population. Patients with meandering main pancreatic duct (MMPD) were more likely to belong to the IPMN group (odds ratio [OR] 6.4). The N-shape, which is one form of MMPD, associated with cystic mural nodules (OR 5.9), which are one of the worrisome features. The presence of ansa pancreatica associated with more extent cysts in the pancreas (OR 12.8). In conclusion, IPMN patients exhibit more often MMPD than control patients.