Fast or Slow? A Comparison Between Two Transcranial Electrical Stimulation Techniques for Eliciting Motor-Evoked Potentials During Supratentorial Surgery

Purpose: Few and contradictory data are available regarding intraoperative seizures during surgery for low-grade gliomas. Aim of this study was to evaluate possible risk factors for the occurrence of IOS. Methods: The authors performed a retrospective analysis of 155 patients affected by low-grade gliomas and tumor-related epilepsy, who underwent surgery in our Department, between 2007 and 2018. A statistical analysis was performed by means of univariate and multivariate regression to evaluate any possible correlation between seizure occurrence and several demographic, clinical, neurophysiological, and histopathological features. Results: Intraoperative seizure occurred in 39 patients (25.16%) with a total of 62 seizure events recorded. Focal seizures were the prevalent seizure type: among them, 39 seizures did not show motor signs, being those with only electrographic and/or with cognitive features the most represented subtypes. Twenty-six seizures occurring during surgery were not spontaneous: direct cortical stimulation with Penfield paradigm was the most prevalent evoking factor. The univariate analysis showed that the following prognostic factors were statistically associated with the occurrence of intraoperative seizure: the awake technique (P ¼ 0.01) and the interictal epileptiform discharges detected on the baseline electrocorticography (ECoG) (P , 0.001). After controlling for confounding factors with multivariate analysis, the awake surgery and the epileptic ECoG pattern kept statistical significance. Conclusions: The awake surgery procedure and the epileptic ECoG pattern are risk factors for intraoperative seizure. ECoG is mandatory to detect electrographic seizures or seizures without motor signs.