Imaging findings of abdominal extra pancreatic lesions associated with autoimmune pancreatitis: CT and MRI findings

Objective: To investigate the imaging characteristics of abdominal extra pancreatic lesions associated with autoimmune pancreatitis (AIP). Methods: Twenty-three patients with AIP proved through histo-pathological or clinical diagnosis were investigated retrospectively. Abdominal extra pancreatic lesions occurred in 17 of them. CT scans were performed in 14 patients and MR imaging in 9 patients (including both of CT and MRI in 6 patients). Results: All 23 patients showed enlargement of the pancreas, with diffuse (n = 14), focal (n = 7) or mixed (n = 2) type, with heterogeneously decreased enhancement and gradually delayed enhancement. A 'capsule-like' rim was present around the lesions in 16 cases. Bile duct involvement was observed in 16 patients, including bile duct dilatation with lower common bile duct wall thickening and enhancement in 12 patients, as well as bile duct dilatation without wall thickening and bile duct wall enhancement without bile duct dilatation seen in 2 patients respectively. Renal involvement was observed in 4 patients. CT and MR imaging revealed single (in 2 patients) or multiple (in 2 patients), iso or hyper-attenuating. With plain CT, it revealed hypo-intense with T₂WI, decreased enhancement lesions in the renal cortex. One mass-like lesion in the right renal showed gradually delayed enhancement. Retro-peritoneal fibrosis was seen in 4 patients, which involved abdominal aorta wall (in 2 patients) and ureters (in 1 patient) as well. Gradual delayed enhancement of retro-peritoneal fibrosis was seen during dynamic contrast-enhancement. Abdominal lymphadenopathy at hepatic portal was observed in 1 patient. Conclusions: Abdominal extra pancreatic lesions associated with AIP show characteristic imaging findings. CT and MRI modalities may be helpful in the diagnosis of AIP. (authors)