[1] Kyoto Univ, Grad Sch Med, Dept Hlth & Environm Sci, Sakyo Ku, Kyoto 6068501, Japan
[2] Kyoto Univ, Grad Sch Med, Dept Neurosurg, Kyoto 6068501, Japan
[3] Ohara Med Ctr, Dept Neurosurg, Fukushima, Japan
[4] Sapporo Med Univ, Grad Sch Med, Dept Neurol Surg, Sapporo, Hokkaido, Japan