1. Department of Neurosurgery, Teikyo University Ichihara Hospital, Ichihara City, Chiba, Japan
2. Teaching and Research Support Center, Tokai University School of Medicine, Boseidai, Isehara City, Kanagawa, Japan
3. Department of Pathology, Tokai University School of Medicine, Boseidai, Isehara City, Kanagawa, Japan