Imaging characteristics of abdominal organs in autoimmune pancreatitis

Objective To investigate the imaging characteristics of abdominal organs in autoimmune pancreatitis (AIP) . Methods Twenty-five patients with AIP that had been diagnosed by histopathological or clinical findings were studied retrospectively.Computed tomography (CT) was performed for 21 patients and magnetic resonance imaging (MRI) for 14 patients, with 10 patients undergoing both CT and MRI. Results Imaging findings revealed that all 25 patients had enlarged pancreas, including diffuse (n=16, 64.0%) , focal (n=7, 28.0%) , or mixed (n=2, 8.0%) types.Lesions showed isodensity (n=13, 61.9%) or mild hypodensity (n=8, 39.1%) .One case showed several small cystic lesions within and around the pancreas.Imaging of the pancreatic lesions revealed that most cases were isointense or mildly hypointense on T1WI and mildly hyperintense on T2WI.All but two of the displayed lesions were detected as high-signal intensity areas on DWI.Dynamic contrast enhanced imaging of the lesions demonstrated "snow-like" heterogeneous and delayed gradual enhancement.A "capsule-like" rim was present around the lesions in 18 cases (72.0%) .The main pancreatic duct was irregular in seven patients (28.0%) and slightly dilated in five patients (20.0%) .Bile duct involvement was observed in 17 patients (68.0%) .Renal involvement was observed in four patients (16.0%) .Retroperitoneal fibrosis was found in four patients (16.0%) .Abdominal lymphadenopathy involving the hepatic portal was observed in one patient (4.0%) . Conclusion Patients with AIP have characteristic imaging findings for the pancreas and other abdominal organs.CT and MRI modalities play a very important role in the diagnosis of AIP.