1. Department of Neurosurgery, Tsukuba Medical Center Hospital, Tsukuba, Ibaraki, Japan
2. Department of Neurosurgery, Koyama Memorial Hospital, Kashima, Ibaraki, Japan
3. Department of Neurosurgery, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
4. Division of Stroke Prevention and Treatment, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan
5. Department of Neurosurgery, Saitama Medical Center, Dokkyo Medical University, Koshigaya, Saitama, Japan
6. Department of Neuro-Endovascular Therapy, Toranomon Hospital, Tokyo, Japan
7. Department of Neurosurgery, National Hospital Organization Mito Medical Center, Higashi-Ibaraki, Ibaraki, Japan