1. Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Tokyo, Japan;
2. Department of Neurosurgery, Tohoku University, Graduate School of Medicine, Sendai, Miyagi, Japan;
3. Department of Neurosurgery, Kohnan Hospital, Sendai, Miyagi, Japan;
4. Department of Neurosurgery, Hokkaido University, Graduate School of Medicine, Sapporo, Hokkaido, Japan;
5. Department of Neurosurgery, Hokkaido Neurosurgical Memorial Hospital, Sapporo, Hokkaido, Japan; and
6. Department of Neurosurgery, Hiroshima University Hospital, Hiroshima, Japan