1. Department of Neurosurgery, Institute of Clinical Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan
2. Katsuta Hospital Mito GammaHouse, Hitachi-naka, Japan
3. Department of Neurosurgery, Ibaraki Prefectural Central Hospital, Kasama, Japan
4. Department of Pathology, Ibaraki Prefectural Central Hospital, Kasama, Japan