1. Department of Neurosurgery, Jikei University School of Medicine Kashiwa Hospital, Kashiwa-shi, Chiba 277-8567, Japan
2. Department of Neurosurgery, Keio University School of Medicine, Shinjuku-ku, Tokyo 160-8582, Japan
3. Division of Diagnostic Pathology, Keio University School of Medicine, Shinjuku-ku, Tokyo 160-8582, Japan
4. Department of Neurosurgery, Kagawa University Hospital, Kita-gun, Kagawa 761-0793, Japan
5. Department of Neurosurgery, Jikei University School of Medicine, Minato-ku, Tokyo 105-8461, Japan