A case of concurrent pancreatic intraepithelial neoplasia and type 1 autoimmune pancreatitis with marked pancreatic duct dilatation.

The case patient was a previously healthy 82-year-old male. Abdominal ultrasound during a medical check-up revealed a dilatation of the main pancreatic duct, and the patient was referred to our hospital for closer examination. Contrast-enhanced computed tomography (CT) revealed a low-density mass of 20 mm in the pancreatic head-body transitional area. Magnetic resonance cholangiopancreatography (MRCP) revealed marked dilatation of the main pancreatic duct and branches in the body-tail. On endoscopic ultrasonography (EUS), a hypoechoic mass with irregular shape was detected, which was consistent with the area of pancreatic duct stenosis. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) and pancreatic juice cytology were performed; however, there were no malignant findings. Serum IgG4 levels had increased to 299 mg/dL. Cancer of the pancreatic head was suspected and a pancreaticoduodenectomy was thus performed. Macroscopic findings included a white mass with indistinct border in the constricted part of the pancreatic duct and mottled fatty replacement of the pancreatic head. Pathologically, a large amount of IgG4-positive plasma cells was found in the white mass, with storiform fibrosis and obstructive phlebitis, which led to the diagnosis of type 1 autoimmune pancreatitis (AIP). Furthermore, scattered low-high grade pancreatic intraepithelial neoplasia lesions were observed throughout the pancreatic head, separately from the AIP lesion. This is an interesting case that suggests an association between AIP and pancreatic cancer. We report the case with a review of relevant literature.