Various applications of intraoperative electrocorticography for epileptogenic tissue mapping in awake glioma surgery

Abstract New-onset epilepsy is a symptomatic expression of diffuse glioma and lowers the quality of life. Surgical resection could extend beyond the traditional lesionectomy and include the epileptic focus when permitted by neurological function. Intraoperative electrocorticography (ioECoG) is used during epilepsy surgery to estimate the epileptogenic tissue by mapping the irritative zone. We aimed to determine the added value of ioECoG for postoperative seizure control in patients with non-refractory, glioma-related seizures. We retrospectively included patients who underwent ioECoG-assisted (awake) tumor resection. The ioECoG tailoring strategy was based on electrographic seizures and interictal discharges (sporadic spikes, continuous spiking patterns, and sharp waves). The extent of resection (EOR) and the residual tumor volume (cm3) were quantified from pre- and postoperative magnetic resonance imaging. We used the Weibull regression model for multivariate time to event (seizure recurrence) analyses. Fifty patients underwent ioECoG-assisted surgery. IoECoG recorded eight (16%) spontaneous electrographic seizures. Seventeen patients had residual interictal discharges after tumor resection. Residual interictal discharges were significantly associated with shorter seizure-free period after surgery (HR = 3.1 [1.3 – 7.2], p-value = 0,01). This effect was especially prominent in primary high-grade glioma resections. Residual tumor volume and EOR did not associate with seizure outcome. We sampled 14 interictal spike-positive brain tissues (three inside and 11 outside the MRI abnormalities) for additional histopathological analyses. Tumor cells were found in all specimens. The overall sensitivity of interictal spikes for tumor infiltration was 78% (95%CI [56 – 93]) and the specificity was 100%. IoECoG could serve multiple purposes in brain tumor surgery. It can assist in intraoperative seizure detection. Complete resection of epileptic discharges may improve seizure outcome independently of rest tumor volume or EOR. IoECoG could help guide supramaximal resection to improve seizure control and assist patient counseling. Furthermore, interictal spikes might serve as markers for intraoperative tumor identification.