1. Department of Neurosurgery, Showa General Hospital, Kodaira, Tokyo, Japan
2. Department of Neurosurgery, Faculty of Medicine, The University of Tokyo, Tokyo, Japan
3. Department of Neurosurgery, Asama General Hospital, Saku, Nagano, Japan
4. Department of Neurosurgery, Saitama Medical Center, Saitama Medical University, Kawagoe, Saitama, Japan