Context: The differential diagnosis between autoimmune pancreatitis and pancreatic cancer is sometimes difficult, especially for those patients in whom laboratory and radiological criteria are lacking.
Case report: A 72-year-old woman was found to have a tumor in the head of the pancreas. Laboratory data showed no abnormal values, including gammaglobulins or autoantibodies. Endoscopic retrograde cholangiopancreatography showed extrinsic stenosis of the main pancreatic and lower common bile ducts. Computed tomography showed a lesion in the head of the pancreas. With a tentative diagnosis of head of the pancreas cancer, the patient underwent pancreaticoduodenectomy. Macroscopically, a tumor 2 cm in diameter not having clear margins was evident in the head of the pancreas. Histological examination showed the infiltration of lymphocytes, plasma cells, and eosinophils with lymphoid follicles around the main pancreatic duct. Immunohistological examination demonstrated that the main pancreatic duct was surrounded by abundant IgG4-positive plasma cells.
Conclusions: The patient was diagnosed as having autoimmune pancreatitis on the basis of the immunohistological findings alone, without any well-defined criteria such as high serum level of IgG4 and presence of autoantibodies before or after surgery.