CT and MRI features

Patients with autoimmune pancreatitis (AIP) commonly present with vague abdominal pain, jaundice, or weight loss, and CT is often the first imaging study obtained. Characteristic CT findings of AIP include diffuse parenchymal enlargement of the pancreas and capsule-like rim. The pancreatic border commonly becomes featureless with effacement of the lobular contour of the pancreas. However, it may present as focal or segmental enlargement of the pancreas or low-density mass, and differentiation with pancreatic cancer may be difficult. Vascular involvement may be sometimes seen. Differentiation from pancreatic cancer can be difficult in such atypical cases. Enhancement pattern of pancreatic parenchyma (decreased enhancement during early phase and increased enhancement during delayed phase of contrast administration), lack of pancreatic duct dilatation, as well as presence of other organ (extrapancreatic) involvement are helpful findings in making the correct diagnosis of AIP. Other uncommon findings include pancreatic pseudocyst and calcification. FDG-PET and MRI with diffusion-weighted imaging may be helpful when CT findings are inconclusive.