1. Department of Neurosurgery, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan
2. Department of Pathology, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan
3. Present address: Department of Pathology, Yamaguchi University Graduate, School of Medicine, Minami-kogushi, Ube, Yamaguchi, Japan
4. Center for Clinical Research, Department of Preventive Medicine and Public Health, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan
5. Department of Neurosurgery, Saiseikai Utsunomiya Hospital, Takebayashi, Utsunomiya, Tochigi, Japan
6. Division of Diagnostic Pathology, Keio University School of Medicine, Shinanomachi, Shinjuku-ku, Tokyo, Japan
7. Department of Neurosurgery, Fujita Health University School of Medicine, Kutsukake-cho, Toyoake, Aichi, Japan