[1] Kyoto Univ, Grad Sch Med, Dept Neurosurg, Kyoto, Japan
[2] Natl Cerebral & Cardiovasc Ctr, Dept Neurosurg, Suita, Osaka, Japan
[3] Hokkaido Univ, Grad Sch Med, Dept Neurosurg, Sapporo, Hokkaido, Japan
[4] Univ Toyama, Grad Sch Med & Pharmaceut Sci, Dept Neurosurg, Toyama, Japan
[5] Nagaoka Chuo Gen Hosp, Dept Neurosurg, Nagaoka, Niigata, Japan
[6] Tohoku Univ, Grad Sch Med, Dept Neurosurg, Sendai, Miyagi, Japan
[7] Tohoku Univ, Sch Publ Hlth, Grad Sch Med, Div Epidemiol,Dept Hlth Informat & Publ Hlth, Sendai, Miyagi, Japan