Is Diffusion-Weighted MRI Useful for Differentiation of Small Non-Necrotic Cervical Lymph Nodes in Patients with Head and Neck Malignancies?

Objective: To evaluate the usefulness of measuring the apparent diffusion coefficient (ADC) in diffusion-weighted magnetic resonance imaging to distinguish benign from small, non-necrotic metastatic cervical lymph nodes in patients with head and neck cancers. Materials and Methods: Twenty-six consecutive patients with head and neck cancer underwent diffusion-weighted imaging (b value, 0 and $800s/mm^2$) preoperatively between January 2009 and December 2010. Two readers independently measured the ADC values of each cervical lymph node with a minimum-axial diameter of ${\geq}5$ mm but < 11 mm using manually drawn regions of interest. Necrotic lymph nodes were excluded. Mean ADC values were compared between benign and metastatic lymph nodes after correlating the pathology. Results: A total of 116 lymph nodes (91 benign and 25 metastatic) from 25 patients were included. Metastatic lymph nodes (mean ${\pm}$ standard deviation [SD], $7.4{\pm}1.6$ mm) were larger than benign lymph nodes (mean ${\pm}SD$, $6.6{\pm}1.4$ mm) (p = 0.018). Mean ADC values for reader 1 were $1.17{\pm}0.31{\times}10^{-3}mm^2/s$ for benign and $1.25{\pm}0.76{\times}10^{-3}mm^2/s$ for metastatic lymph nodes. Mean ADC values for reader 2 were $1.21{\pm}0.46{\times}10^{-3}mm^2/s$ for benign and $1.14{\pm}0.34{\times}10^{-3}mm^2/s$ for metastatic lymph nodes. Mean ADC values between benign and metastatic lymph nodes were not significantly different (p = 0.594 for reader 1, 0.463 for reader 2). Conclusion: Measuring mean ADC does not allow differentiating benign from metastatic cervical lymph nodes in patients with head and neck cancer and non-necrotic, small lymph nodes.