1. Department of Neurosurgery, Graduate School of Medicine, Yokohama City University, Yokohama, Japan;
2. Department of Neurosurgery, The University of Tokyo Graduate School of Medicine, Tokyo, Japan;
3. Department of Radiology, Graduate School of Medicine, Yokohama City University, Yokohama, Japan;
4. Department of Diagnostic Radiology, Graduate School of Medicine, Tokyo Medical and Dental University, Tokyo, Japan