18F-FDG PET for retropharyngeal lymph node metastasis in oropharyngeal and hypopharyngeal cancers: impact on diagnosis and prediction analysis

Abstract

Retropharyngeal lymph node (RPLN) metastasis is a poor prognosticator in oropharyngeal and hypopharyngeal cancers. The purpose of this study is to evaluate the impact of F-fluorodeoxyglucose positron emission tomography (F-FDG PET) on the diagnosis and predictor analysis of RPLN in these cancers. We enrolled patients with oropharyngeal and hypopharyngeal cancers before receiving definitive treatment. Staging was performed by F-FDG PET and conventional imaging modalities. Differences in RPLN metastasis detection rates were compared. Independent predictors of RPLN involvement were also assessed. A total of 224 patients were investigated. RPLN involvement was identified in 17% of the study patients. In 18% of the 38 patients with RPLN involvement, RPLN metastases were identified by F-FDG PET only. Only 4% of the patients with oropharyngeal cancer and RPLN metastasis were not identified without the use of F-FDG PET, compared with 46% of patients with hypopharyngeal cancer. In multivariate analysis, posterior pharyngeal wall tumor (P=0.02) or the presence of ipsilateral level V lymph node metastasis (P=0.025) were independent predictors of RPLN involvement in hypopharyngeal cancer. In oropharyngeal cancer, no factors retained their independent significance. We concluded that F-FDG PET is helpful in detecting RPLN metastasis in hypopharyngeal cancer. The presence of ipsilateral level V lymph node metastasis or tumors originating from the posterior pharyngeal wall can predict RPLN involvement in hypopharyngeal cancer and might represent an indication for elective irradiation of this nodal basin. However, regional lymph node involvement is not an independent predictor in oropharyngeal cancer. The predictor for RPLN metastasis seems to change after the introduction of PET.