1. Cerebrovascular Diseases Research Institute, Xuanwu Hospital of Capital Medical University, Beijing 100053, P.R. China
2. Department of Neurosurgery, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, P.R. China
3. Department of Neurosurgery, The Affiliated Hospital of Weifang Medical College, Weifang, Shandong 261031, P.R. China