1. Department of Neurosurgery, Institute of Medicine, University of Tsukuba, Tsukuba, Japan
2. Department of Neurosurgery, Mito Kyodo General Hospital, Tsukuba University Hospital, Mito Area Medical Education Center, Mito, Ibaraki, Japan
3. Department of Neurosurgery, Southern Tohoku Hospital, Koriyama, Japan
4. Department of Neurosurgery, Tsukuba Memorial Hospital, Tsukuba, Japan
5. Department of Neurosurgery, University of Tsukuba Hospital, Tsukuba, Japan
6. Department of Neurosurgery, University of Tsukuba, Tsukuba, Japan
7. Department of Neurosurgery, Dokkyo Medical University, Mibu, Japan