1p/19q-codeletion in the context of an IDH mutation is the genetic hallmark of oligodendrogliomas26 and is a strong favorable prognostic factor for overall survival20,23,27 and a strong predictor of response to radiochemotherapy.28–31 More relevant to intraoperative decision-making, Wijnenga et al.2 examined the impact on overall survival of the extent of surgical resection, measured as volume of residual tumor seen on postoperative contrast magnetic resonance imaging, in molecularly stratified low grade gliomas (WHO grade II astrocytomas and oligodendrogliomas). This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).