1. Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551, Japan
2. Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima 890-8520, Japan
3. Department of Neurosurgery, Onomichi General Hospital, Onomichi 722-8508, Japan