The histological findings of type 1 autoimmune (IgG4-related) pancreatitis (AIP), also called lymphoplasmacytic sclerosing pancreatitis, encompass diverse lesions in which marked lymphoplasmacytic infiltration and fibrosis envelop the pancreatic ducts, lobules, peripancreatic adipose tissue, and blood vessels. The concept of this disease was proposed based on histological analyses that revealed a pathological picture characterized by storiform fibrosis and obliterative phlebitis. Accordingly, the histological findings are essential to making the diagnosis which is more important, even, than the finding of IgG4-positive plasmacytic infiltration, which is nonspecific in the absence of the appropriate background morphology.
In contrast to type 1 AIP, type 2 AIP presents with inflammation centered on exocrine tissue extending from the pancreatic ducts to within the lobules. Neutrophil infiltration of the pancreatic duct lumen and/or epithelium (granulocytic epithelial lesion; GEL) is characteristic of type 2 AIP, and when GEL is noted within the interlobular pancreatic ducts, a definitive diagnosis can be made.
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