Type 1 and Type 2 Autoimmune Pancreatitis: Distinctive Clinical and Pathological Features, but Are There Any Differences at Magnetic Resonance? Experience from a Referral Center

Objectives This study aimed to evaluate magnetic resonance imaging findings of autoimmune pancreatitis (AIP) and to find radiological patterns that could differentiate type 1 and type 2 AIP. Methods Eighty-four patients with diagnosis of AIP were enrolled. Image analysis included pancreatic signal intensity abnormalities, enhancement pattern, extrapancreatic involvement, and main pancreatic duct alterations. Results Pancreatic parenchyma resulted in hypointensity on T1-weighted images in 65 (98.5%) of 66 cases in type 1 and in 17 (94.5%) of 18 in type 2 (P > 0.05) and in hyperintensity on T2-weighted images in 41 (62%) of 66 and in 15 (83.4%) of 18, respectively (P > 0.05). Lesions were hypovascular in 64 (97%) of 66 cases in type 1 and in 16 (88.9%) of 18 in type 2 with delayed contrast retention in 56 (84.8%) of 66 and in 17 (94.5%) of 18, respectively (P > 0.05). Autoimmune cholangitis was found in 29 (43.9%) of 66 patients with type 1 and in 3 (16.7%) of 18 with type 2 (P = 0.02); renal involvement was observed in 20 (30.3%) of 66 and 1 (5.5%) of 18, respectively (P = 0.02). Both subtypes presented with multiple stenoses (P > 0.05). Dilation of upstream duct was more frequent in type 1 (P = 0.02). Conclusions Magnetic resonance imaging is useful in detecting extrapancreatic involvement, typically seen in type 1. Dilation of the upstream duct suggests type 1 AIP.