Differentiation of autoimmune pancreatitis from pancreatic cancer by diffusion-weighted MRI.

OBJECTIVES: We sought to clarify the clinical utility of diffusion-weighted magnetic resonance imaging (DWI) for differentiating autoimmune pancreatitis (AIP) from pancreatic cancer.

METHODS: Thirteen AIP patients underwent DWI before therapy, and six of them underwent DWI after steroid therapy. The extent and shape of high-intensity areas were compared with those of 40 pancreatic cancer patients. Apparent diffusion coefficient (ADC) values were calculated in the AIP area before and after steroid therapy in pancreatic cancer patients and in a normal pancreatic body.

RESULTS: On DWI, AIP and pancreatic cancer were detected as high-signal intensity areas. The high-intensity areas were diffuse (n=4), solitary (n=6), and multiple (n=3) in AIP patients, but all pancreatic cancer patients showed solitary areas (P<0.001). A nodular shape was significantly more frequent in pancreatic cancer, and a longitudinal shape was more frequently found in AIP (P=0.005). ADC values were significantly lower in AIP (1.012+/-0.112 x 10(-3) mm(2)/s) than in pancreatic cancer (1.249+/-0.113 x 10(-3) mm(2)/s) and normal pancreas (1.491+/-0.162 x 10(-3) mm(2)/s) (P<0.001). Receiver operating characteristic analysis yielded an optimal ADC cutoff value of 1.075 x 10(-3) mm(2)/s to distinguish AIP from pancreatic cancer. After steroid therapy, high-intensity areas on DWI disappeared or were markedly decreased, and the ADC values of the reduced pancreatic lesions increased almost to the values of normal pancreas.

CONCLUSIONS: DWI is useful for detecting AIP and for evaluating the effect of steroid therapy. ADC values were significantly lower in AIP than in pancreatic cancer. An ADC cutoff value may be useful for distinguishing AIP from pancreatic cancer.