Small nodules which could indicate the early phase of autoimmune pancreatitis

We present a case with small pancreatic nodules, which could indicate the early phase of autoimmune pancreatitis (AIP). A 68-year-old man was referred to our hospital for further diagnostic evaluation of a pancreatic mass detected on abdominal ultrasonography screening for epigastric discomfort. Abdominal ultrasonography and endoscopic ultrasonography revealed a low echoic lesion measuring approximately 1 cm with an irregular margin in the body of the pancreas. Computed tomography revealed a tumor in the portal venous phase of enhancement; hence, a distal pancreatectomy was performed. On histology, a marked lymphocyte- and plasma cell-dominant inflammatory cell infiltrate was observed in the nodule. There was another smaller nodule consisting of moderate lymphoplasmacytic infiltration in the 2-cm distal portion of the pancreas. Lymphoplasmacytic infiltration was also observed around the main pancreatic duct in the pancreatic stump. In the parenchyma, other than these 3 portions, the normal lobular structure was well preserved. Little storiform fibrosis and obliterative phlebitis were observed in the resected specimen. On immunohistochemical staining, plasma cells showing strong immunoreactivity for immunoglobulin G4 were observed within these two nodules and around the main pancreatic duct at the cut surface. This case could indicate the early phase and multicentricity of AIP.