Mass‐forming autoimmune pancreatitis and pancreatic carcinoma: Differential diagnosis on the basis of computed tomography and magnetic resonance cholangiopancreatography, and diffusion‐weighted imaging findings

Abstract Purpose: To differentiate mass‐forming autoimmune pancreatitis (AIP) from pancreatic carcinoma by means of analysis of both computed tomography (CT) and magnetic resonance imaging (MRI) findings. Materials and Methods: Ten patients with mass‐forming AIP diagnosed by revised clinical criteria of Japan Pancreas Society and 70 patients with pathologically proven pancreatic carcinoma were enrolled in this retrospective study. Two radiologists independently evaluated the CT and MR imaging findings. The sensitivity, specificity, and odds ratio of significant imaging findings and combinations of findings were calculated. Results: Seven findings were more frequently observed in AIP patients: (i) early homogeneous good enhancement, (ii) delayed homogeneous good enhancement, (iii) hypoattenuating capsule‐like rim, (iv) absence of distal pancreatic atrophy, (v5) duct penetrating sign, (vi) main pancreatic duct (MPD) upstream dilatation ≤ 4 mm, and (vii) an apparent diffusion coefficient (ADC) ≤ 0.88 × 10 −3 mm 2 /s. When the findings of delayed homogeneous enhancement and ADC ≤ 0.88 × 10 −3 mm 2 /s were both used in diagnosis of mass‐forming AIP, a sensitivity of 100% and a specificity of 100% were achieved. When 4 of any of the 7 findings were used in the diagnosis of AIP, a sensitivity of 100% and a specificity of 98% were achieved. Conclusion: Analysis of a combination of CT and MR imaging findings allows for highly accurate differentiation between mass‐forming AIP and pancreatic carcinoma. J. Magn. Reson. Imaging 2012;35:827–836. © 2011 Wiley Periodicals, Inc.