[1] Kumamoto Univ, Grad Sch Med Sci, Dept Neurosurg, Kumamoto, Japan
[2] Kyushu Mem Hosp, Dept Neurosurg, Kumamoto, Japan
[3] Kumamoto Univ, Grad Sch Med Sci, Dept Anesthesiol, Kumamoto, Japan
[4] Univ Tokushima, Grad Sch Med, Dept Clin Neurosci, Inst Hlth Biosci, Tokushima 770, Japan
[5] Univ Tokushima, COE Program 21st, Tokushima 770, Japan