Lymphoplasmacytic infiltration and fibrosis are primarily subepithelial around the pancreatic duct in patients with autoimmune pancreatitis (AIP). This process encompasses the pancreatic ducts and narrows their lumen. Diffuse irregular narrowing of the main pancreatic duct (MPD) is rather specific to AIP. Pancreatic cancer typically infiltrates and destroys the epithelium of the pancreatic duct. These periductal histopathological differences result in the variance in pancreatographic findings between AIP and pancreatic cancer. Pancreatographic findings such as absence of obstruction of the MPD, skip lesions of the MPD, side branch derivation from the narrowed portion of the MPD, MPD involvement over >3 cm, and maximal upstream MPD diameter of <5 mm are each suggestive of AIP. However, it is difficult to differentiate a short narrowing of the MPD in AIP from stenosis in pancreatic cancer, and there are some pancreatic cancer cases showing pancreatographic findings similar to those of AIP. MRCP does not replace ERCP in initial diagnosis from the inability to reliably detect MPD narrowing due to the inferior resolution, but may have a role in the follow-up of AIP patients. IgG4 immunostaining of biopsy specimens obtained from the major duodenal papilla is useful for supporting a diagnosis of AIP.
KeywordsPancreatic Cancer Main Pancreatic Duct Obstructive Jaundice Pancreatic Cancer Patient Hilar Bile Duct
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