Autoimmune pancreatitis is a rare type of pancreatitis that is characterized by diffuse swelling of the pancreas and irregular stenosis of the pancreatic ductal system ("sclerosing" pancreatitis), caused by autoimmune processes. Previous reports have shown the complete form of the disease, but very few have presented follow-up imagings from the beginning to the complete form. We, herein, report a case of autoimmune pancreatitis starting as a localized form. A-56-year-old Japanese man developed obstructive jaundice. Ultrasonography showed a hypoechoic mass in the head of the pancreas, and endoscopic retrograde pancreatography (ERP) showed localized stenosis of the pancreatic duct in the head of the pancreas. Computed tomography (CT) showed enlargement, with a capsule-like rim, in the head of the pancreas. Internal biliary tube drainage was performed to relieve the obstructive jaundice. The patient was followed-up under the tentative diagnosis of localized "mass-forming" pancreatitis. Four months after the drainage, CT showed diffuse swelling of the pancreas, with a capsule-like rim, and ERP demonstrated diffuse irregular narrowing of the pancreatic duct. Glucose intolerance was noted for the first time. Steroid was given as a diagnostic treatment for autoimmune pancreatitis. Two months after initiation of the steroid treatment, the ERP findings were normal, and CT showed a normal pancreas. The biliary tube was removed, and the glucose intolerance was subsequently alleviated. To summarize, we report a case of autoimmune pancreatitis starting as localized "mass-forming" pancreatitis with a peripheral rim on imagings. It is very important to be well aware of the presence of the localized form of autoimmune pancreatitis.
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