1. Sapporo Azabu Neurosurgical Hospital, Hokkaido, Japan
2. Sapporo Yamanoue Hospital, Hokkaido, Japan
3. Department of Neurology, Hokkaido University of Medicine, Hokkaido, Japan
4. Health Sciences University of Hokkaido, Hokkaido, Japan
5. Department of Neurosurgery, Hokkaido University of Medicine, Hokkaido, Japan