1. Department of Neurosurgery, Iwate Medical University
2. Department of Neurosurgery, Iwate Prefectural Chubu Hospital, Kitakami, Iwate
3. Department of Neurosurgery, Noshiro Kosei Medical Center, Noshiro, Akita
4. Department of Neurosurgery, Hachinohe Red Cross Hospital, Hachinohe, Aomori, Japan