The Pattern of Cervical Lymph Node Metastasis and Risk Factors of Retropharyngeal Lymph Node Metastasis Based on Magnetic Resonance Imaging in Different Sites of Hypopharyngeal Carcinoma

BACKGROUND: This study was to determine the patterns of regional lymph node (LN) spread and the risk factors of retropharyngeal lymph node (RPLN) metastasis based on magnetic resonance imaging (MRI) in hypopharyngeal squamous carcinoma (HPC) to improve clinical target volume (CTV) delineation. METHODS: A cohort of 326 consecutive patients of HPC in a single institute were retrospectively reviewed. All patients underwent MRI prior to initial treatment, and the diagnosis based on MRI of the LN metastasis was confirmed by all radiation oncologists in the head and neck group during twice weekly chat rounds. Statistical analysis of data was using chi-square test and multivariant logistic regression model in SPSS 22.0 software. RESULTS: The LN metastasis rate of all patients in this cohort was 90.5% (295/326). Level IIa/b and level III were the most frequently involved regions followed by level IV and retropharyngeal region. Skip metastasis only occurred in 6.4% (19/295). Univariate and multivariate analysis demonstrated that primary tumor subsites were located in the posterior pharyngeal wall (P=0.002), bilateral cervical LN metastasis (P=0.020), larger volume of primary gross target (GTVp, P=0.003), and larger volume of LN gross target (GTVnd, P=0.023) were significantly associated with RPLN metastasis. CONCLUSION: The regional LN spread of HPC follows an ordered pattern as level II is the most frequently involved area followed by level III, level IV, and RPLN. RPLN metastasis is more likely to occur in patients with primary site of posterior pharyngeal wall, large tumor burden, or bilateral neck LN metastasis. Therefore, it is highly recommended that the RPLN should be included into CTV for patients who have these risk factors.