toshihiko wakabayashi department of neurosurgery, nagoya university, graduate school of medicine toshihiko iuchi division of neurological surgery, chiba cancer center naohiro tsuyuguchi department of neurosurgery, osaka city university graduate school of medicine ryo nishikawa department of neuro-oncology/neurosurgery, saitama international medical center, saitama medical university yoshiki arakawa department of neurosurgery, kyoto university graduate school of medicine takashi sasayama department of neurosurgery, kobe university graduate school of medicine