Comparison of radiological and histological findings in autoimmune pancreatitis.

Objective: Autoimmune pancreatitis displays radiological findings that are sometimes difficult to differentiate from pancreatic carcinoma. To understand the essential radiological features of autoimmune pancreatitis (AIP), we compared imaging and histological findings in resected AIP specimens.

Methods: Findings of ultrasonography, computed tomography, endoscopic retrograde cholangiopancreatography and angiography were examined retrospectively for 6 patients who underwent pancreatoduodenectomy on suspicion of pancreatic carcinoma, and compared with histological findings of the resected specimens.

Results: Ultrasonography showed an enlarged hypoechoic pancreas with sausage-like appearance and no lobulation in the contour of the pancreas. On computed tomography imaging, delayed enhancement of the swollen pancreatic parenchyma became evident. Dense lymphoplasmacytic infiltration with fibrosis involving peripancreatic tissue was observed throughout almost the entire pancreas. Periductal non-occlusive fibrosis with lymphoplasmacytic infiltration induced narrowing of the pancreatic duct. Stenosis of the common bile duct is frequently associated with autoimmune pancreatitis and is induced by diffuse thickening of the duct wall by the same inflammatory process as that of the pancreas. The fibroinflammatory process also involves blood vessels.

Conclusions: Characteristic radiological findings of autoimmune pancreatitis are induced with systemic histological changes of lymphoplasmacytic infiltration with fibrosis, and differ from schirrous invasion of pancreatic carcinoma.