Patterns of Retropharyngeal Node Metastasis in Nasopharyngeal Carcinoma

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.

Introduction

Nasopharyngeal carcinoma (NPC) is common among Asians, especially in southern China. The nasopharynx has a well-developed network of lymphatics, and cervical lymphadenopathy is common in NPC. Most patients with NPC (60–90%) have nodal metastases at presentation on computed tomography (CT) or magnetic resonance (MR) imaging 1, 2, 3, 4, 5, 6, 7. Because radiotherapy is the standard treatment of both the primary tumor and nodal metastases in NPC, the pattern of nodal spread has an important bearing on radiotherapy treatment planning. The retropharyngeal lymph nodes (RLN) and cervical Level II nodes have been reported to be the most commonly involved nodal regions 3, 4, 5, 7. Despite the high incidence of metastasis to the RLN in NPC, its prognostic significance has not been fully resolved 8, 9, 10, and the recommendations in published staging systems that pertain to RLN involvement are ambiguous 11, 12. Data describing RLN spread patterns based on radiographic observations will provide critical guidance for further research on prognostic significance and staging categories.

The relationships between RLN metastasis and primary tumor extensions and cervical nodal metastases are useful for clarifying the patterns of lymphatic drainage and nodal metastases in NPC but have not yet been thoroughly investigated. Liu et al.(7) and Chua et al.(8) observed a higher incidence of enlarged RLN associated with oropharyngeal, parapharyngeal, and cervical lymph node involvement. Lam et al.(13) found a statistical association between RLN metastasis and Level II node involvement but not with other groups of neck nodes. Apart from these three articles, there is little published information concerning the relationship between RLN metastasis and tumor extensions in NPC. Furthermore, there is no consensus as to whether RLN are the first-echelon nodes. Retropharyngeal lymph nodes had been regarded as the first-echelon nodes of NPC 3, 14, but the findings of Shu-Hang Ng et al.(15) indicate that RLN are involved less frequently than cervical nodes. The aims of our study were to analyze the incidence, number, and distribution of RLN metastases in a cohort of patients with NPC and to examine through MR imaging the relationship of these metastases with primary tumor extension and cervical lymphadenopathy to document patterns of RLN spread.