Autoimmune pancreatitis with multifocal lesions.

Two cases of a focal type of autoimmune pancreatitis (AIP) with distinct double mass lesions within the pancreas are described. In both patients, computed tomography (CT) showed localized pancreatic masses with delayed enhancement, and magnetic resonance cholangiopancreatography (MRCP) revealed localized stenoses of the main pancreatic duct (MPD) with mild upstream dilatation. Fluorodeoxyglucose positron emission tomography (FDG-PET) examination, performed in one patient, showed intense uptake concordant with tumors. Both patients received pancreatic resection with a presumptive diagnosis of pancreatic carcinoma. Histologic evaluation of the tumors showed marked lymphoplasmacytic infiltration and fibrosis around the large and medium pancreatic ducts, without any evidence of malignancy. Serum IgG4 concentration, measured postoperatively, was elevated in both patients. The characteristic morphological features of AIP are diffuse swelling of the pancreatic parenchyma and diffuse narrowing of the MPD. Recently, a focal type of AIP, which mimics pancreatic carcinoma, has been recognized. Considering the favorable response of AIP to steroid therapy, it is clinically important to differentiate the focal type of AIP from pancreatic carcinoma and to know that AIP sometimes exhibits multiple lesions within the pancreas.