Advances of Intracranial Electroencephalography in Localizing the Epileptogenic Zone

Intracranial electroencephalography（i EEG）provides the best precision in estimating the location and boundary of an epileptogenic zone. Analysis of i EEG in the routine EEG frequency range（0.5-70 Hz） remains the basis in clinical practice. Low-voltage fast activity is the most commonly reported ictal onset pattern in neocortical epilepsy, and low-frequency high-amplitude repetitive spiking is the most commonly reported ictal onset pattern in mesial temporal lobe epilepsy. Recent studies using wideband EEG recording have demonstrated that examining higher（80-1000 Hz） and lower（0.016-0.5 Hz） EEG frequencies can provide additional diagnostic information and help to improve the surgical outcome. In addition,novel computational techniques of i EEG signal analysis have provided new insights into the epileptic network.Here, we review some of these recent advances. Although these sophisticated and advanced techniques of i EEG analysis show promise in localizing the epileptogenic zone,their utility needs to be further validated in larger studies.

Interictal Electrophysiological Source Imaging Based on Realistic Epilepsy Head Model in Presurgical Evaluation:A Prospective Study

Invasive techniques are becoming increasingly important in the presurgical evaluation of epilepsy.Adopting the electrophysiological source imaging(ESI)of interictal scalp electroencephalography(EEG)to localize the epileptogenic zone remains a challenge.The accuracy of the preoperative localization of the epileptogenic zone is key to curing epilepsy.The T1 MRI and the boundary element method were used to build the realistic head model.To solve the inverse problem,the distributed inverse solution and equivalent current dipole(ECD)methods were employed to locate the epileptogenic zone.Furthermore,a combination of inverse solution algorithms and Granger causality connectivity measures was evaluated.The ECD method exhibited excellent focalization in lateralization and localization,achieving a coincidence rate of 99.02%(p<0.05)with the stereo electroencephalogram.The combination of ECD and the directed transfer function led to excellent matching between the information flow obtained from intracranial and scalp EEG recordings.The ECD inverse solution method showed the highest performance and could extract the discharge information at the cortex level from noninvasive low-density EEG data.Thus,the accurate preoperative localization of the epileptogenic zone could reduce the number of intracranial electrode implantations required.

Emerging personalized virtual brain models: next-generation resection neurosurgery for drug-resistant epilepsy?

Recently,a novel workflow known as the virtual epileptic patient(VEP)has been proposed by a research team from Aix Marseille Universitéin their papers published in Lancet Neurology,Science Translational Medicine and Epilepsia.This method involves creating an individualized virtual brain model based on computational modelling,which can facilitate clinical decision-making by estimating the epileptogenic zone and performing the virtual surgery.Here,we summarize brief workflow,strengths,and limitations of VEP,as well as its performance in a retrospective study of 53 patients with drug-resistant focal epilepsy who underwent stereoelectroencephalography.A large-scale clinical trial(NCT03643016)is underway to further assess VEP,which is expected to enroll 356 patients prospectively.As supporting evidence accumulates,the clinical application of VEP has the potential to improve clinical practice,leading to better outcomes and qualities of life of patients.

Prognostic value of high-frequency oscillations combined with multimodal imaging methods for epilepsy surgery

Background:The combination of high-frequency oscillations(HFOs)with single-mode imaging methods has been proved useful in identifying epileptogenic zones,whereas few studies have examined HFOs combined with multimodal imaging methods.The aim of this study was to evaluate the prognostic value of ripples,an HFO subtype with a frequency of 80 to 200 Hz is combined with multimodal imaging methods in predicting epilepsy surgery outcome.Methods:HFOs were analyzed in 21 consecutive medically refractory epilepsy patients who underwent epilepsy surgery.All patients underwent positron emission tomography(PET)and deep electrode implantation for stereo-electroencephalography(SEEG);11 patients underwent magnetoencephalography(MEG).Sensitivity,specificity,positive predictive value,negative predictive value,and accuracy in predicting surgical outcome were calculated for ripples combined with PET,MEG,both PET and MEG,and PET combined with MEG.Kaplan-Meier survival analyses were conducted in each group to estimate prognostic value.Results:The study included 13 men and 8 women.Accuracy for ripples,PET,and MEG alone in predicting surgical outcome was 42.9%,42.9%,and 81.8%,respectively.Accuracy for ripples combined with PET and MEG was the highest.Resection of regions identified by ripples,MEG dipoles,and combined PET findings was significantly associated with better surgical outcome(P<0.05).Conclusions:Intracranial electrodes are essential to detect regions which generate ripples and to remove these areas which indicate good surgical outcome for medically intractable epilepsy.With the assistance of presurgical noninvasive imaging examinations,PET and MEG,for example,the SEEG electrodes would identify epileptogenic regions more effectively.