1. Nishinomiya Kyoritsu Neurosurgical Hospital, Imazuyamanakacho, Nishinomiya, Hyogo, Japan
2. Department of Neurosurgery, Osaka Medical College, Daigakucho, Takatsuki, Osaka, Japan
3. Department of Neurosurgery, Graduate school of medicine, Chiba University, Inohana, Chuouku, Chiba, Chiba, Japan
4. Department of Neurosurgery, Yamaguchi University School of Medicine, Minamikogushi, Ube, Yamaguchi, Japan
5. Department of Neurosurgery, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Shikadacho, Okayama, Okayama, Japan
6. Department of Neurosurgery, Saiseikai Yahata General Hospital, Yahata Higashiku Harunocho, Kitakyusyu, Fukuoka, Japan
7. Department of Neurosurgery, Nakamura Memorial Hospital, Chuouku, Sapporo, Hokkaido, Japan