1. Department of Special Medicine, Basic Medicine College, Qingdao University, Qingdao, Shandong 266071, P. R. China
2. Department of Neurosurgery, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266000, P. R. China
3. Department of Otolaryngology Head and Neck Surgery, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266000, P. R. China