1 Department of Thoracic Surgery, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, P. R. China.
2 Department of Esophageal Surgery, The Sixth Affiliated Hospital, Sun Yat-sen University, Guangzhou, Guangdong, P. R. China.
3 Department of Ultrasonography, Guangzhou First People's Hospital, School of Medicine, South China University of Technology, Guangzhou, Guangdong, P. R. China.