Magnetic resonance imaging findings of the mass-forming type of autoimmune pancreatitis: Comparison with pancreatic adenocarcinoma

Purpose: To determine the characteristic magnetic resonance imaging (MRI) features of mass-forming autoimmune pancreatitis (AIP), which allow its differentiation from pancreatic adenocarcinoma (PAC). Materials and Methods: MR images of 37 patients with either pathologically proven, mass-forming AIPs (n = 9) or PACs (n = 28) were retrospectively reviewed. The pancreatic MR protocol included unenhanced images, contrast-enhanced dynamic images, diffusion-weighted imaging (DWI), and MR-cholangiopancreatography (MRCP). Two reviewers analyzed the MR images regarding the number, location, morphologic features, and enhancement degree and pattern of the lesions as well as secondary changes of the pancreatic parenchyma, the biliary and pancreatic ducts. The size and apparent diffusion coefficient (ADC) values of the lesions were measured. Results: Although sensitivities were low (28.6%44.4%), specificities of multiplicity, capsule-like rim enhancement, and skipped stricture of the biliary or pancreatic duct in mass-forming AIP were high (100%). Sensitivities and specificities of irregular or geographic shape, delayed enhancement, and a low ADC value <1.26 X 10-3 mm2/s in mass-forming AIP were favorable (71.4%83.3% and 78.5%89.3%). Conclusion: Although to differentiate mass-forming AIP from pancreatic cancer is difficult, the combination of MRI findings including contrast-enhanced dynamic images, MRCP, and DWI can be a help. J. Magn. Reson. Imaging 2012;36:188197. (c) 2012 Wiley Periodicals, Inc.