P18-F Intraoperative high-frequency electrocorticography in structural epilepsy

Abstract

Background High-frequency oscillations (HFOs) are associated with epileptogenesis. Nevertheless, clinical implications of this marker are still limited. The objective of this study was to determine the diagnostic efficacy of high-frequency electrocorticography (HF-ECoG) in structural epilepsy surgery. Material and methods This is a retrospective study of 32 patients who underwent surgery for tumor-associated (subgroup 1, 11 pts) or pharmacoresistant (subgroup 2, 21 pts) epilepsy in Polenov Russian Neurosurgical Institute in 2017–2018. Comparison group included patients with tumors without epilepsy. HF-ECoG in all patients was recorded with subdural grid electrodes (AdTech, USA) before and after lesion resection via Mitsar-EEG-202 hardware (Russia). Epilepsy surgery outcome was assessed in 12 months postoperatively. The recordings were visually analyzed and HFO index (HFOi) was calculated. HFOi is the maximum of HFO-compromised seconds in all artifact-free minute-long epochs of HF-ECoG. Results Postoperatively in 25% of the cases in subgroup 1 and 50% of subroup 2 patients had seizures. Preresective HF-ECoG in comparison group showed morphologically similar HFOs to those in epilepsy patients. Preresective HFOi was higher in subgroup 2 vs 1 (mean - 27 ± 13.2% vs 13.6 ± 11.3%), probably due to the duration and severity of the disease. Presence of HFOs in postresective HF-ECoG in epilepsy patients was not associated with worse outcome. Significant reduction of HFOi correlated with good seizure outcome. Specificity equaled 85.7%, while sensitivity was 58.3%. Conclusions HFOs reflect the processes of epileptogenesis. HF-ECoG provides an opportunity to predict seizure outcome. However, this technique is still not considered self-sufficient for epilepsy surgery.