1. Department of Neurosurgery, Qingdao Municipal Hospital, Qingdao University, Qingdao, Shandong 266000, P.R. China
2. Department of Neurosurgery, RenMin Hospital of Jimo, Qingdao, Shandong 266200, P.R. China
3. Department of Neurosurgery, The Affiliated Hospital of Qingdao University, Qingdao, Shandong 266000, P.R. China