Diffusion-weighted imaging to differentiate metastatic from non-metastatic retropharyngeal lymph nodes in nasopharyngeal carcinoma

Objectives: To evaluate the diagnostic value of diffusion-weighted MRI for differentiating metastatic from non-metastatic retropharyngeal lymph nodes (RLNs) in patients with nasopharyngeal carcinoma (NPC). Methods: Untreated patients with NPC (n = 145) were scanned with both morphological MRI and diffusion-weighted imaging (DWI). RLNs (n = 335) were classified as metastatic on the basis of response to therapy as assessed on follow-up MRI. Morphological (short-and long-axial diameters) and functional [mean apparent diffusion coefficient (ADC) and minimum ADC values] parameters of the RLNs were derived from DWI and compared between metastatic and non-metastatic groups. A receiver operating characteristic curve and the area under the curve were used to evaluate the effectiveness of individual criteria and to generate threshold values to diagnose RLN metastases. Results: Statistically significant differences between metastatic and non-metastatic RLNs were found for all four parameters derived from DWI (p < 0.001). At threshold values, accuracies of the ADC-based criteria (0.938 and 0.965 for mean and minimum ADC values, respectively) were greater than that of size-based criteria (0.838 and 0.809 for short-and long-axial diameters). The minimum ADC value at the threshold of 0.89 x 10(-3) mm(2) s(-1) was the most effective of all parameters in differentiating metastatic from non-metastatic RLNs with the sensitivity of 95.7%, specificity of 95.1% and accuracy of 96.5%. Conclusions: DWI is feasible for differentiating metastatic RLNs from non-metastatic nodes in patients with NPC with high accuracy, and the minimum ADC derived from DWI could serve as a standard clinical marker for disease status.