Description of the surgical procedure
The neck dissection method was selected in accordance with the preoperative examination, primary tumour extent and regional lymph node metastasis. Patients with N0–N1 underwent ipsilateral Ⅱ–Ⅳ selective neck dissection, patients with N2 underwent ipsilateral Ⅱ–Ⅴ neck dissection, and patients with N3 underwent ipsilateral Ⅰ–Ⅴ + contralateral Ⅱ–Ⅳ neck dissections. If the tumour crosses the midline, bilateral neck dissection is performed; level VI and retropharyngeal lymph node dissections were performed for patients with T3–T4 and N2b or above.