Patterns of lymph node metastases from nasopharyngeal carcinoma: an analysis of 3100 patients based on MRI

Objective: To investigate the patterns of lymph node metastases from nasopharyngeal carcinoma (NPC) based on magnetic resonance imaging (MRI) and to provide a basis for neck irradiation field in intensity-modulated radiation therapy. Methods: From 2010 to 2013, 3100 patients newly diagnosed with NPC who underwent MRI were analyzed. All images were evaluated by the multi-disciplinary treatment group for NPC to analyze lymph node metastases. The locations of lymph nodes were determined by the RTOG consensus guidelines published in 2003. Results: Of 3 100 patients, 2679 (86.42%) had lymph node metastases; the detailed distribution was as follows: lateral retropharyngeal region (2012 patients, 64.90%; 6 patients were also in the medial group), level II_b(2341 patients, 75.52%; 492 had the upper border reaching half of C₁ vertebra and 115 had the upper border reaching the skull base), level II_a(1798 patients, 58.00%), level III (1184 patients, 38.19%), level IV (350 patients, 11.29%; 28 had the lower border beyond the RTOG recommended boundary), level V (995 patients, 32.10%; 91 had the lymph nodes beyond the RTOG recommended boundary), level I_b (115 patients, 3.71%), and parotid region (40 patients, 1.29%), Extensive ipsilateral lymph node metastases were seen in patients with lymph nodes metastases in levels IV and V, and the total numbers of involved nodes were ≥ 6 and 7. Skip metastasis occurred in 6 patients (0.19%). Conclusions: Metastases to retropharyngeal lymph nodes are seen mainly in the lateral group but rarely in the medial group. The upper border of level II lymph nodes should be the skull base. Lymph node metastases from NPC are in an orderly manner, and skip metastasis is rarely seen. When level IV/V lymph nodes are involved, there might exist metastases beyond the RTOG recommended boundary. In case of extensive ipsilateral lymph node metastases, the parotid region might be involved. (authors)