1. Department of Neurosurgery; Chiba Hokuso Hospital, Nippon Medical School; 1715 Kamagari, Inzai-City Chiba Japan
2. Department of Neurology; Tokyo University; Tokyo Japan
3. Department of Neurosurgery; Kushiro Rosai Hospital; Hokkaido Japan
4. Department of Neurology; Sapporo Yamanoue Hospital; Hokkaido Japan
5. Department of Neurosurgery; Nippon Medical School; Tokyo Japan