A 67-year-old man was admitted to our hospital to evaluate a pancreatic tumor. The serum level of IgG4 was elevated and abdominal CT showed a solid mass accompanied with a cystic mass in the tail of the pancreas. FDGPET revealed high accumulation at the site of the pancreatic solid mass. ERCP revealed obstruction of the main pancreatic duct in the body of the pancreas. EUS-FNA did not reveal any plasma cells of autoimmune pancreatitis or cancer cell. We diagnosed pancreatic cystic tumor associated with autoimmune pancreatitis preoperatively, and performed distal pancreatectomy. Gross inspection of the resected specimen showed a solid mass associated with a cystic lesion with mucus in the tail of the pancreas. Pathological examination showed fibrosis with infiltration of IgG4 positive plasma cells and the cystic mass consisted of mucus and single cuboidal epithelium. We diagnosed pancreatic retention cyst containing mucus, associated with autoimmune pancreatitis.
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