Radiologic Criteria of Retropharyngeal Lymph Node Metastasis in Nasopharyngeal Carcinoma Treated with Radiation Therapy

Purpose: To determine the appropriate radiologic criteria of metastatic retropharyngeal lymph nodes (RLNs) in patients with nasopharyngeal carcinoma (NPC). Materials and Methods: After institutional review board approval and informed consent, 303 consecutive NPC patients treated with definitive radiation therapy were examined after completion of therapy. RLNs were classified as metastatic on the basis of the results of magnetic resonance (MR) imaging follow-up. The receiver operating characteristic curve and area under the curve were determined to assess the accuracy of different size criteria in the diagnosis of RLN metastasis. Results: Initial MR images revealed 523 RLNs in 265 patients. Two hundred sixty-four (50.5%) RLNs positive for malignant involvement were confirmed in 177 patients. The remaining 259 (49.5%) nodes were classified as negative for benign process at follow-up. The minimal axial diameter was found to be more accurate than the maximal axial diameter for assessing metastatic RLNs. The most accurate size criterion of metastatic RLNs was a minimal axial diameter of 6 mm or larger, resulting in an accuracy of 87.5% (457 of 522). Central necrosis or groups of two or more of RLNs had a 100% specificity for diagnosis of RLN metastases. Conclusion: The radiologic criteria that should be used for assessment of RLN metastases in NPC patients are nodes with a minimal axial diameter 6 mm or larger, any node with central necrosis, groups of two or more RLNs, or any medial RLN; these criteria may be useful in tumor staging and treatment planning. (C) RSNA, 2010