1. Department of Neurosurgery, Hiroshima University, Graduate School of Biomedical and Health Sciences, Hiroshima;
2. Fujieda Heisei Memorial Hospital, Fujieda, Shizuoka;
3. Department of Neurosurgery, Kagoshima University, Graduate School of Medical and Dental Sciences, Kagoshima; and
4. Sapporo Azabu Neurosurgical Hospital, Sapporo, Hokkaido, Japan