Purpose: To explore the pattern of metastasis to retropharyngeal lymph nodes (RLN) and its relationship with tumor range in nasopharyngeal carcinoma (NPC) patients by using magnetic resonance imaging.
Methods and materials: Magnetic resonance images of 618 NPC patients were reviewed. Nodes were classified as metastatic on the basis of size criteria, the presence of nodal necrosis, and extracapsular spread.
Results: A total of 597 involved RLN were detected in 392 patients (63.4%). The sites of RLN metastasis included occipital bone, 37 (6.2%); first cervical vertebra (C1), 453 (75.9%); second cervical vertebra (C2), 104 (17.4%); and third cervical vertebra (C3), 3 (0.5%). The incidence of RLN involvement was less than that of Level IIb node involvement (72.2% vs. 86.5%) in 543 patients with lymphadenopathy. The incidence of RLN metastasis was significantly higher in cases of parapharyngeal space invasion or involvement of Level II, Level III, Level IV, and/or Level V nodes and significantly lower in N0 and Stage I disease. Conversely, the incidence of RLN metastasis did not differ significantly among T1, 2, 3, and 4 disease or among Stage II, III, and IV disease.
Conclusions: Level IIb nodes, rather than RLN, seem to be the first-echelon nodes in NPC. The incidence of RLN metastasis decreases steadily from level C1 to level C3. Retropharyngeal lymph node metastasis correlates well with involvement of the parapharyngeal space and metastases to Level II, III, IV, and/or V nodes but not with T stage.