Histological and radiological features of type 1 AIP. A: Pancreas is inflamed with inflammatory cell infiltration and storiform fibrosis (H&E, ×100). B: Inflammatory cells consist of predominantly lymphocytes and plasma cells, and occasional eosinophils (H&E, ×400). C: A vein branch is obliterated by sclerosing inflammation (obliterative phlebitis) (Elastica van Gieson, ×200). D: Many IgG4+ plasma cells are identified (IgG4 immunostaining, ×400). E: ERCP shows diffuse irregularity of the pancreatic duct. F: The pancreas is diffusely enlarged with a peri-pancreatic rim (arrows) (contrast-enhanced CT).