Prevalence and Risk Factors for Retropharyngeal and Retro-Styloid Lymph Node Metastasis in Hypopharyngeal Carcinoma

Abstract

We evaluated the prevalence and identified the risk factors for retropharyngeal and retro-styloid lymph node metastasis (LNM) in patients with hypopharyngeal carcinoma (HPC). This was achieved using a combination of MR and FDG-PET/CT images. Two board-certified radiation oncologists, who experienced 16 and 18 years in the diagnosis and treatment of head and neck cancers retrospectively reviewed pretreatment FDG-PET/CT images and contrast-enhanced thin-slice CT and MR images of 155 patients with HPC who underwent radiotherapy. Observers assessed these images without prior knowledge of the patient's clinical information and disagreements were resolved by consensus. The radiological diagnostic criteria for lateral retropharyngeal LNM (RPLNM) and retro-styloid LNM (RSLNM) were a short-axis diameter of ≥5 mm and/or necrosis and/or abnormal FDG uptake. Any visible medial RPLN was defined as LNM. RPLNM was confirmed in 20 (13%) patients. Of these, 10 (6%) had ipsilateral RPLNM, 5 (3%) had contralateral RPLNM, and 5 (3%) had bilateral RPLNM. No patients were diagnosed with medial RPLNM. Fisher's exact test revealed tumor site (p = 0.006), T category (p = 0.049), and cervical LNM (p < 0.001) to be significantly associated with RPLNM. Logistic regression analysis revealed posterior wall (PW) tumors (odds ratio [OR]: 4.128, 95% confidence interval [CI]: 1.339-12.727; p = 0.014) and bilateral or contralateral cervical LNM (OR: 11.577, 95% CI: 2.135-62.789; p = 0.005) to be significantly correlated with RPLNM. The RPLNM was found in 9 (32%) of the 28 patients with PW tumors. Of these 9 patients, 2 (7%) had ipsilateral RPLNM, 3 (11%) had contralateral RPLNM, and 4 (14%) had bilateral RPLNM. Fisher's exact test revealed the PW tumors to be significantly associated with contralateral RPLNM (p < 0.001). Retro-styloid LNM (RSLNM) was confirmed in two (1%) patients, both of whom had ipsilateral RSLNM with lymph nodes (LNs) of ≥15 mm in the upper limit of ipsilateral level II. Fisher's exact test revealed the LN of ≥15 mm in the upper limit of ipsilateral level II to be significantly associated with ipsilateral RSLNM (p = 0.001). The RPLNM was identified in 13% of patients with HPC. The PW tumors and bilateral or contralateral cervical LNM were risk factors for RPLNM; particularly, PW tumors were a specific risk factor for contralateral RPLNM. Although the RSLNM was rare, LNs of ≥15 mm in the upper limit of ipsilateral level II were a risk factor for ipsilateral RSLNM.