IDH1 and oligodendroglial tumor: Multivariable analysis indicated that a preoperative seizure was not an independent prognostic factor in diffuse astrocytic and oligodendroglial tumors (P = 0.57), and high-grade tumor (WHO grade III or IV) and wild-type IDH were negative prognostic factors for patient survival (P = 0.002 and P = 0.014, respectively).