Utility of diffusion-weighted MRI in characterization of adrenal lesions

OBJECTIVE. The purpose of our study was to evaluate the utility of apparent diffusion coefficient (ADC) values for characterizing adrenal lesions and determine if diffusionweighted imaging (DWI) can distinguish lipid-rich from lipid-poor adenomas. MATERIALS AND METHODS. We retrospectively evaluated 160 adrenal lesions in 156 patients (96 women and 60 men; mean age, 63 years). ADCs and signal intensity (SI) decrease on chemical shift imaging were measured in adrenal lesions with a wide variety of pathologies. Lipid-rich and lipid-poor adenomas were identified by unenhanced CT. The overall predictive power of ADC, SI decrease, and lesion size were determined by receiver operating characteristic (ROC) analysis. Areas under the ROC curve (AUC) were compared for equivalence using nonparametric methods. Sensitivity, specificity, and positive and negative predictive values were calculated. Correlation coefficients were used to assess ADCs versus percentage SI decrease and ADCs versus CT attenuation. RESULTS. ADCs of adrenal malignancies (median, 1.67 × 10 ^-3 mm²/s; interquartile range, 1.41-1.84 × 10 ^-3 mm²/s) were not different compared with those of benign lesions (1.61 × 10^-3 mm²/s; 1.27-1.96 × 10^-3 mm²/s; p > 0.05). Cysts (2.93 × 10 ^-3 mm²/s; 2.70-3.09 × 10^-3 mm ²/s) showed higher ADCs than the remaining adrenal lesions (p < 0.05). The median ADCs of lipidrich adenomas did not differ from those of lipid-poor ones (p > 0.05). The CT attenuation had no negative or positive correlation with the ADCs of adrenal adenomas (r = -0.05, p = 0.97). CONCLUSION. Unlike lesion size and percentage decrease in SI, the ADCs were not useful in distinguishing benign from malignant adrenal lesions. Lipid-poor adenomas could not be distinguished from lipid-rich adenomas and all other nonfatty lesions of the adrenal gland with DWI.