Figure 2.

Retroperitoneal fibrosis occurring before the onset of autoimmune pancreatitis. A 65-year-old man developed hydronephrosis and renal failure. A, B: Soft tissue was observed surrounding the abdominal aorta and common iliac artery. No abnormality was found in the pancreas. The patient was diagnosed with idiopathic retroperitoneal fibrosis, and started receiving prednisolone (PSL) at the dose of 40 mg/d. The dose was gradually reduced over approximately 6 mo and discontinued. The hydronephrosis improved, and the patient continued to be followed up; C, D: Swelling of the pancreas observed on computed tomography images taken about 1 yr and 6 mo after the discontinuation of PSL. Compared with the initial observation, retroperitoneal fibrosis improved, but persisted. The serum immunoglobulin G4 level was 366 mg/dL. At that point, the patient was diagnosed with autoimmune pancreatitis, and started receiving PSL again at the dose of 40 mg/d. The swelling of the pancreas and retroperitoneal fibrosis were improved.