We previously reported that lymphoplasmacytic infiltration around the pancreatic duct, a characteristic histological finding of autoimmune pancreatitis (AIP), can be visualized on endoscopic ultrasonography (EUS) as pancreatic duct wall thickening [1]. This study evaluated the utility of EUS-detected pancreatic duct wall thickening in distinguishing AIP from pancreatic neoplasms.

We included 47 patients who underwent EUS and were diagnosed with AIP according to the International Consensus Diagnostic Criteria (ICDC), as well as 339 patients with histologically confirmed pancreatic neoplasms treated at our institution from March 2017 to September 2025. Detection rates of pancreatic duct wall thickening on EUS were compared between the two groups. Pancreatic duct wall thickening was defined as hypoechoic thickening of the duct wall with a thin hyperechoic surface layer. All EUS images and video recordings were retrospectively reviewed.

In the AIP group, patient characteristics were as follows: 37 males (78.7%), median age 73 years (range 42–87), diffuse-type disease in 26 cases (55.3%), elevated serum IgG4 levels in 36 cases (76.6%), and extrapancreatic involvement in 13 cases (27.7%). In the pancreatic neoplasm group, there were 166 males (49.0%) with a median age of 76 years (range 24–95). Histological diagnoses included pancreatic ductal adenocarcinoma (n=271), neuroendocrine neoplasms (n=47), and intraductal papillary mucinous neoplasm (IPMN) (n=21). Pancreatic duct wall thickening was detected significantly more often in the AIP group (82.6%, 38/46) than in the tumor group (1.5%, 5/339) (p < 0.01). In patients with focal-type AIP, thickening was observed within or around the focal lesions. Among 12 AIP patients who underwent EUS after steroid therapy, improvement of duct wall thickening was observed in 10 cases (83.3%). All five pancreatic neoplasm cases showing duct wall thickening underwent surgical resection. Three cases corresponded to focal pancreatic atrophy associated with carcinoma in situ. The remaining two corresponded to intraductal extension of IPMN, where the thickened duct wall was continuous with intraductal papillary projections.

Pancreatic duct wall thickening on EUS is frequently observed in AIP and serves as a useful marker for differentiating it from pancreatic neoplasms.