1. Department of Neurological Surgery, Chiba University Graduate School of Medicine, Chiba;
2. Department of Neurosurgery, Chiba Cerebral and Cardiovascular Center, Ichihara;
3. Tokyo Gamma Unit Center, Tsukiji Neurological Clinic, Tokyo; and
4. Department of Neurosurgery, Seikeikai Chiba Medical Center, Chiba, Japan