Abstract: Objective To investigate the clinical value of 3.0T MR diffusion weighted imaging(DWI) in differentiating benign and malignant retropharyngeal lymph nodes. Methods The clinical and imaging data of 44 patients with retropharyngeal lymph nodes RLNs were collected. All of the patients underwent MRI examination, and were divided into benign group(13 cases) and malignant group(31 cases) according to pathological biopsy. The DWI signal and apparent dispersion coefficient（ADC）value were compared, and the receiver operating characteristic(ROC) curve was used to calculate the optimal critical value of ADC and area under the curve(AUC), to evaluate the diagnostic efficacy and to analyze the difference of signal and ADC value of different malignant lymph nodes. Results A total of 65 lymph nodes in the posterior lateral pharyngeal group of 44 patients were included in the analysis, the ADC values of benign group(23 nodes) and malignant group(42 nodes) were（0.833±0.095）×10^－3 mm²/s and（0.737±0.136）×10^－3 mm²/s , respectively, and the difference was statistically significant(P=0.004). The ADC value of 65 lymph nodes(both benign and malignant) were used to determine benign and malignant lymph nodes and draw ROC curve, and AUC was 0.756. With 0.769×10^-3 mm²/s as the best diagnostic cut-off value, the sensitivity for the diagnosis of benign and malignant was 78.3%, and the specificity was 64.3%. The ADC values of the malignant lymph nodes in the signal uniform group and the inhomogeneous group were(0.688±0.092)×10^-3 mm²/s and(0.787±0.156)×10^-3 mm²/s, respectively, and the difference was statistically significant(P= 0.016). The ADC values of the maximum short diameter of malignant lymph nodes ≤10 mm goup and >10 mm group were(0.745±0.146)×10-3 mm2/s and(0.731±0.131)×10^-3 mm²/s, respectively , and the difference was not statistically significant(P=0.748). Conclusion The ADC value of 3.0T MR DWI is an important reference for the differential diagnosis of benign and malignant postpharyngeal lymph nodes. Moreover, DWI can further improve the detection rate of small metastatic retropharyngeal lymph nodes with the maximum short diameter <5 mm.

Key words: Nasopharyngeal neoplasm, Retropharyngeal lymph node, Magnetic resonance imaging, Diffusion weighted imaging