1. Department of Neurosurgery, Chiba Rosai Hospital, Ichihara City, Chiba, Japan
2. Department of Neurosurgery, Chiba University Graduate School of Medicine, Chiba City, Chiba, Japan
3. Department of Neurosurgery, Tsukiji Neurological Clinic, Tokyo, Japan
4. Department of Neurosurgery, Chiba Cerebral and Cardiovascular Center, Chiba, Japan
5. Department of Neurosurgery, Seikei-kai Chiba Medical Center, Chiba, Japan