1. a Department of Neurosurgery, Kyoto University Medical School
2. b Institute for Frontier Medical Sciences, Kyoto University, 53 Kawahara-cho Shogoin, Sakyo-ku, Kyoto 606, Japan
3. c Institute for Frontier Medical Sciences, Kyoto University, 53 Kawahara-cho Shogoin, Sakyo-ku, Kyoto 606, Japan
4. d Department of Neurosurgery, Kyoto University Medical School
5. e Department of Neurosurgery, Kyoto University Medical School
6. f Department of Neurosurgery, Kyoto University Medical School
7. g Institute for Frontier Medical Sciences, Kyoto University, 53 Kawahara-cho Shogoin, Sakyo-ku, Kyoto 606, Japan