Department of General Surgery, Beijing Friendship Hospital, Capital Medical University & National Clinical Research Center for Digestive Diseases, No.95 Yong-an Road, Xi-Cheng District, Beijing, 100050, China. National Clinical Research Center for Digestive Diseases, Beijing Friendship Hospital, Capital Medical University, No.95 Yong-an Road, Xi-Cheng District, Beijing, 100050, China. Department of Radiology, Beijing Friendship Hospital, Capital Medical University, No.95 Yong-an Road, Xi-Cheng District, Beijing, 100050, China. Department of General Surgery, Beijing Friendship Hospital, Capital Medical University & National Clinical Research Center for Digestive Diseases, No.95 Yong-an Road, Xi-Cheng District, Beijing, 100050, China. zhangpg@yahoo.com. Department of General Surgery, Beijing Friendship Hospital, Capital Medical University & National Clinical Research Center for Digestive Diseases, No.95 Yong-an Road, Xi-Cheng District, Beijing, 100050, China. zhangzht@ccmu.edu.cn.