Role of diffusion-weighted imaging in the discrimination of benign and metastatic parotid area lymph nodes in patients with nasopharyngeal carcinoma.

To assess the utility of apparent diffusion coefficient (ADC) determined on diffusion-weighted MR imaging (DWI) to differentiate between benign and malignant parotid area lymph nodes (PLN) in nasopharyngeal carcinoma (NPC) patients. Thirty-nine consecutive NPC patients with a total of 40 enlarged, biopsied PLNs underwent DWI examination. ADC values for benign and malignant PLNs were measured and compared. Receiver operating characteristic (ROC) curve analysis was to evaluate the optimal threshold level of ADC values for metastatic PLNs. The kappa was to assess the degree of agreement between histopathological diagnoses and ADC values, or imaging features of PLNs on MRI. We found the mean ADC value for benign PLNs was markedly higher than malignant PLNs. A threshold ADC of 1.01 × 10-3 mm2/s was associated with a sensitivity of 85.7% and a specificity of 72.7% (area under the curve: 0.84). A moderate agreement was observed between the histopathological diagnosis and the threshold of ADC value (k value: 0.483). However, short axis diameter, necrosis, extranodal extension, and regional grouping of PLNs on MRI showed only a fair agreement with the histopathological diagnosis (k value: 0.257, 0.305, 0.276, and 0.205, respectively). Therefore, DWI may be a promising technique to differentiate metastatic from benign PLNs.