A prospective study on the utility of diffusion-weighted and quantitative chemical-shift magnetic resonance imaging in the distinction of adrenal adenomas and metastases.

OBJECTIVE: The purpose of this study was to assess the utility of diffusion-weighted and quantitative chemical-shift magnetic resonance imaging in the differentiation of adrenal adenomas and metastases.

METHODS: One hundred eight patients (45 men and 63 women; mean age, 57 years) with 126 adrenal masses were prospectively evaluated by magnetic resonance imaging in this study. Signal intensity and apparent diffusion coefficient (ADC) measurements were performed on axial in- and opposed-phase T1-weighted gradient-echo images and on diffusion-weighted images, respectively. Adrenal signal intensity index (ASII), adrenal-to-spleen chemical-shift ratio (ASR), and ADC values were assessed separately. The threshold values of more than 16.5% for ASII and less than 0.71 for ASR were regarded as highly suggestive of adenoma diagnosis. We also investigated whether a cutoff value for ADC could be found in distinguishing adenomas from metastases. Final diagnoses of adrenal lesions were based on follow-up imaging, histopathologic proof, and adrenal washout study. Apparent diffusion coefficient values of adenomas and metastases were compared by using the Student t test, and ASII and ASR values of the lesions were compared by using the Mann-Whitney U test, and a P < 0.05 was accepted as statistically significant. Receiver operating characteristic curve analysis and sensitivity, specificity, positive and negative predictive values, and overall accuracies were calculated.

RESULTS: Final analysis yielded 96 adenomas and 30 metastases. With the commonly used 16.5% threshold value for ASII, we obtained a 94.8% sensitivity, 93.3% specificity, 84.8% positive predictive value, and 97.8% negative predictive value. The overall accuracy was found as 94.4%. When we applied a 0.71 threshold value for ASR, it yielded a 91.7% sensitivity, 100% specificity, 78.9% positive predictive value, and a 100% negative predictive value. The overall accuracy was 93.6%. The mean ADC values were found to be 1.35 ± 0.19 × 10⁻³ mm²/s and 1.32 ± 0.34 × 10⁻³ mm²/s for adenomas and metastases, respectively. The difference between the groups with these ADC values was not statistically significant (P = 0.673). The receiver operating characteristic analysis could not determine a clear cutoff value for the differentiation of adenomas from metastases.

CONCLUSIONS: We can advocate that a chemical-shift magnetic resonance imaging using quantitative parameters (ie, ASII and ASR formulas) has an important role in the distinction of adenomas from metastases. These 2 techniques seem to provide close sensitivity, specificity, and accuracy levels. But diffusion-weighted imaging using quantitative ADC measurements is not of value in this differential diagnosis because of the substantial overlapping of ADC values between adenomas and metastases.