Branch Duct Intraductal Papillary Mucinous Neoplasms of the Pancreas Involving Type 1 Localized Autoimmune Pancreatitis with Normal Serum IgG4 Levels Successfully Diagnosed by Endoscopic Ultrasound-guided Fine-needle Aspiration and Treated without Pancreatic Surgery

We herein report a 68-year-old man with branch duct intraductal papillary mucinous neoplasms of the pancreas (BD-IPMNs) involving type 1 localized autoimmune pancreatitis (AIP) with normal serum IgG4 levels. Although he was referred to our medical center due to suspicion of pancreatic cancer concomitant with BD-IPMNs, endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) revealed a mass suspected of being pancreatic cancer to be type 1 AIP. Steroid administration notably reduced the mass. Although the clinical diagnosis of pancreatic masses in patients with IPMN can be occasionally challenging, performing a pathological examination by EUS-FNA may prevent unnecessary pancreatic surgery in cases of possible AIP.