Focal Pancreatic Parenchymal Atrophy in Main Duct Intraductal Papillary Mucinous Neoplasms of the Pancreas.

Introduction Although upstream pancreatic atrophy (UPA) is a characteristic finding in main duct intraductal papillary mucinous neoplasms (MD-IPMNs) of the pancreas, the relationship between MD-IPMNs and focal pancreatic parenchymal atrophy (FPPA), which is an indicator of early-stage pancreatic ductal adenocarcinoma, remains unclear. Thus, this study aimed to investigate the relationship. Methods From the 49 patients diagnosed with MD-IPMNs using the resected specimens from June 2003 to December 2023, 19 patients were selected to clarify the clinical characteristics of FPPA for MD-IPMN patients. The primary outcome measure was the frequency of FPPA/UPA. Secondary outcome measures were (1) the locational relationship between MD-IPMN and FPPA and (2) the clinicopathological differences between those atrophic types. Results FPPA and UPA were observed in 4 (21%) and 12 (63%) patients, respectively. When the clinicopathological factors of FPPA and UPA patients were compared, only the diameter of the main pancreatic duct (MPD) significantly differed (median MPD diameter: 6 mm vs. 11 mm, p = 0.017). Of the four patients with FPPA, the histological extent of the MD-IPMN lesion was within that of FPPA in three patients (75%) and was concordant with that of FPPA only in one patient (25%). Conclusions FPPAs were detected in approximately 20% of resected MD-IPMNs, and 75% of those MD-IPMNs were histologically included in the area of the FPPAs. Since the MPD diameter was significantly smaller for MD-IPMNs with FPPAs than those with UPAs, MD-IPMNs with FPPAs may be biologically related to the mild dilation of the MPD, such as lesions at an early stage or less mucin secretion.