Esophageal cancer is the eighth most common cancer around the world, with more than 450000 new cases per year. Esophagectomy with radical lymphadenectomy (2-field lymphadenectomy) is the mainstay of treatment in many countries for patients with esophageal cancer. To improve the survival, 3-field lymphadenectomy combined with cervical lymphadenectomy was starTed in 1980s. More potential positive lymph nodes were found during more extended lymphadenectomy, offering more accurate TNM staging, affecting consequent treatment. However，3-field-lymphadenectomy was associated with increased surgical morbidity and mortality. Positron emission tomography (PET) is used for detecting distant metastases and lymphatic involvement. The aim of the study is to evaluate the role of PET in predicting cervical lymph metastases of patients with thoracic esophageal squamous cell carcinoma, and to determine if we can use PET to guide future cervical lymphadenectomy.