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