Preliminary application of MR diffusion weighted imaging in the diagnosing and evaluating therapeutic effect of autoimmune pancreatitis

Objective: To investigate the role of DWI in differentiating autoimmune pancreatitis (AIP) from pancreatic cancer (PC), and in the therapeutic effect evaluation of AIP. Methods: DWI data of 26 cases with AIP, 29 cases with PC and 30 cases with normal pancreas (NP) were analyzed retrospectively. The distribution type and signal feature of lesions in cases with AIP or PC were evaluated by Chi-squared test. ADC values were measured and compared among 3 groups by Kruskal-Wallis test. ADC values of AIP and PC were analyzed by using R0C curve to determine the optimal threshold and diagnostic efficiency. ADC values were compared in AIP (n = 15) before and after steroid therapy by paired t test. Results: Diffuse lesions were detected in 21 cases with AIP and 3 cases with PC, while focal lesions in 5 cases with AIP and 26 cases with PC (χ² = 27.64, P < 0.01). On DWI, most of AIP (n = 19) and PC (n = 24) showed hyper intense signal, while a few of AIP (n = 7) and PC (n = 5) showed iso-intense signal (χ² = 0.75, P > 0.05). The median ADC values of AIP, PC and NP were 1.15 × 10^-3, 1.35 × 10^-3, 1.59 × 10^-3 mm²/s, respectively; and the difference was statistically significant (H = 45.60, P < 0.01). ROC analysis yielded an optimal ADC cutoff value of 1.255 × 10^-3 mm²/s (80.8% sensitivity, 79.3% specificity and 0.871 area under curve for the diagnosis of AIP). ADC values of AIP (n = 15) were markedly increased from the baseline (1.10 ± 0.19) × 10^-3 to (1.57 ± 0.12) × 10^-3 mm²/s after steroid therapy (t = -10.14, P < 0.01). Conclusions: DWI may be useful for diagnosing and evaluating the effect of steroid therapy in AIP. ADC values of AIP were significantly lower than those of pancreatic cancer and normal pancreas. After steroid therapy, ADC values were markedly increased in AIP. (authors)