Autoimmune pancreatitis (AIP) is a distinctive form of chronic pancreatitis that can mimic pancreatobiliary malignancies. If AIP is properly diagnosed, it can be treated without laparotomy or pancreatic resection due to its dramatic response to steroid therapy. In addition to elevated serum IgG4 levels, IgG4 immunostaining of involved tissue is often used to support the diagnosis of AIP. The major duodenal papilla is a conduit between the duodenum and the pancreatobiliary system and occasionally reflects underlying pancreatobiliary disorders. Previous studies demonstrated that IgG4-positive lymphoplasmacytic infiltration was detected in the major duodenal papilla in connection to the pancreatic head in patients with AIP, and IgG4 immunostaining of biopsy specimens obtained from the major papilla could support a preoperative diagnosis of AIP. This review discusses macro- and microscopic findings of the major duodenal papilla of AIP patients, especially focusing on the diagnostic value of IgG4 immunostaining of duodenal papillary biopsy specimens.
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