Intraoperative Electrocorticography Research Articles

Seizure Outcome After Intraoperative Electrocorticography-Tailored Epilepsy Surgery: A Systematic Review and Meta-Analysis.

Tailoring epilepsy surgery using intraoperative electrocorticography (ioECoG) has been debated, and modest number of epilepsy surgery centers apply this diagnostic method. We assessed the current evidence to use ioECoG-tailored epilepsy surgery for improving postsurgical outcome. PubMed and Embase were searched for original studies reporting on ≥10 cases who underwent ioECoG-tailored surgery for epilepsy, with a follow-up of at least 6 months. We used a random-effects model to calculate the overall rate of patients achieving favorable seizure outcome (FSO), defined as Engel class I, ILAE class 1, or seizure-free status. Meta-regression was used to investigate potential sources of heterogeneity. We calculated the odds ratio (OR) for estimating variables on FSO:ioECoG vs non-ioECoG-tailored surgery (if included studies contained patients with non-ioECoG-tailored surgery), ioECoG-tailored epilepsy surgery in children vs adults, temporal (TL) vs extratemporal lobe (eTL), MRI-positive vs MRI-negative, and complete vs incomplete resection of tissue that generated interictal epileptiform discharges (IEDs). A Bayesian network meta-analysis was conducted for underlying pathologies. We assessed the evidence certainty using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE). Eighty-three studies (82 observational studies, 1 trial) comprising 3,631 patients with ioECoG-tailored surgery were included. The overall pooled rate of patients who attained FSO after ioECoG-tailored surgery was 74% (95% CI 71-77) with significant heterogeneity, which was predominantly attributed to pathologies and seizure outcome classifications. Twenty-two studies contained non-ioECoG-tailored surgeries. IoECoG-tailored surgeries reached a higher rate of FSO than non-ioECoG-tailored surgeries (OR 2.10 [95% CI 1.37-3.24]; p < 0.01; very low certainty). Complete resection of tissue that displayed IEDs in ioECoG predicted FSO better compared with incomplete resection (OR 3.04 [1.76-5.25]; p < 0.01; low certainty). We found insignificant difference in FSO after ioECoG-tailored surgery in children vs adults, TL vs eTL, or MRI-positive vs MRI-negative. The network meta-analysis showed that the odds of FSO was lower for malformations of cortical development than for tumors (OR 0.47 95% credible interval 0.25-0.87). Although limited by low-quality evidence, our meta-analysis shows a relatively good surgical outcome (74% FSO) after epilepsy surgery with ioECoG, especially in tumors, with better outcome for ioECoG-tailored surgeries in studies describing both and better outcome after complete removal of IED areas.

Robust compression and detection of epileptiform patterns in ECoG using a real-time spiking neural network hardware framework

Interictal Epileptiform Discharges (IED) and High Frequency Oscillations (HFO) in intraoperative electrocorticography (ECoG) may guide the surgeon by delineating the epileptogenic zone. We designed a modular spiking neural network (SNN) in a mixed-signal neuromorphic device to process the ECoG in real-time. We exploit the variability of the inhomogeneous silicon neurons to achieve efficient sparse and decorrelated temporal signal encoding. We interface the full-custom SNN device to the BCI2000 real-time framework and configure the setup to detect HFO and IED co-occurring with HFO (IED-HFO). We validate the setup on pre-recorded data and obtain HFO rates that are concordant with a previously validated offline algorithm (Spearman’s ρ = 0.75, p = 1e-4), achieving the same postsurgical seizure freedom predictions for all patients. In a remote on-line analysis, intraoperative ECoG recorded in Utrecht was compressed and transferred to Zurich for SNN processing and successful IED-HFO detection in real-time. These results further demonstrate how automated remote real-time detection may enable the use of HFO in clinical practice.

Intraoperative ECoG in bottom-of-the-sulcus syndrome using a novel flexible strip electrode.

The recording of epileptiform discharges from bottom-of-sulcus focal cortical dysplasia (BOSD) is often difficult during intraoperative electrocorticography (ECoG) due to the deep localization. We describe the use in this scenario of a new-generation electrode strip with high flexibility, easily adapted to cortical gyri and sulci. A right-handed 20-year-old male with drug-resistant focal epilepsy due to BOSD of the inferior frontal gyrus and daily focal aware seizures was evaluated for epilepsy surgery. Based on electroclinical and neuroimaging results, a focal cortectomy guided by ECoG was proposed. ECoG recordings were performed with new-generation cortical strips (Wise Cortical Strip; WCS®) and standard cortical strips. ECoG, performed on the convexity of the frontal cortical surface, recorded only sporadic spikes with both types of strips. Then, after microsurgical trans-sulcal dissection, WCS was molded along the sulcal surface of the suspected BOSD based on 3D-imaging reconstruction, showing continuous/subcontinuous 3-4-Hz rhythmic spike activity from the deepest electrode. Registration after resection of the BOSD did not show any epileptiform activity. Pathology showed dysmorphic neurons and gliosis. No surgical complications occurred. The patient is seizure-free after 12 months. This single case experience shows that highly flexible electrode strips with adaptability to cortical gyrations can identify IEDs originating from deep location and could therefore be useful in cases of bottom of the sulcus dysplasia.

Pediatric Intraoperative Neurophysiologic Mapping and Monitoring in Brain Surgery.

Similar to adults, children undergoing brain surgery can significantly benefit from intraoperative neurophysiologic mapping and monitoring. Although young brains present the advantage of increased plasticity, during procedures in close proximity to eloquent regions, the risk of irreversible neurological compromise remains and can be lowered further by these techniques. More so, pathologies specific to the pediatric population, such as neurodevelopmental lesions, often result in medically refractory epilepsy. Thus, their successful surgical treatment also relies on accurate demarcation and resection of the epileptogenic zone, processes in which intraoperative electrocorticography is often employed. However, stemming from the development and maturation of the central and peripheral nervous systems as the child grows, intraoperative neurophysiologic testing in this population poses methodologic and interpretative challenges even to experienced clinical neurophysiologists. For example, it is difficult to perform awake craniotomies and language testing in the majority of pediatric patients. In addition, children may be more prone to intraoperative seizures and exhibit afterdischarges more frequently during functional mapping using electrical cortical stimulation because of high stimulation thresholds needed to depolarize immature cortex. Moreover, choice of anesthetic regimen and doses may be different in pediatric patients, as is the effect of these drugs on immature brain; these factors add additional complexity in terms of interpretation and analysis of neurophysiologic recordings. Below, we are describing the modalities commonly used during intraoperative neurophysiologic testing in pediatric brain surgery, with emphasis on age-specific clinical indications, methodology, and challenges.

Good Outcome of Resective Epilepsy Surgery in a 1-Year-Old Child with Drug-Resistant Focal Epilepsy with a Novel Pathogenic COL4A1 Mutation.

Pathogenic variants in COL4A1, encoding the α chain of type IV collagen, have been associated with cerebrovascular pathology as well as malformations of cortical development, thereby causing structural epilepsy. This case illustrates successful resective epilepsy surgery in a 12-month-old girl with left occipital focal cortical dysplasia (FCD) associated with a heterozygous splice-donor variant in COL4A1. She presented with drug-resistant focal epilepsy with daily seizures from the age of 2 months, refractory to several combinations of antiseizure medications, as well as mild right-sided hemiparesis and developmental delay. All presurgical diagnostic modalities, including ictal and interictal electroencephalography, magnetic resonance imaging, and ictal fluorodeoxyglucose positron emission tomography, showed congruent findings, pointing toward one single left occipital epileptogenic zone (EZ). We performed a left occipital lobectomy, using intraoperative electrocorticography to confirm the boundaries of the EZ. After surgery, the patient has remained seizure free, and both cognitive and motor developments have improved. Histopathology of the resected brain tissue showed FCD type Ia. Resective epilepsy surgery can have a very good outcome, also in patients with genetic mutations in COL4A1, constituting a less invasive option than the previously used more radical surgical procedures such as hemispherectomy.

Ultrasound-Navigated Multiple Hippocampal Transections: An Anatomical Study.

Multiple hippocampal transection (MHT) is a surgical technique used for the treatment of drug-resistant mesial temporal lobe epilepsy in situations where standard procedures would pose a high risk for memory deterioration. During MHT, the longitudinal fibers of the hippocampus, implicated in epilepsy spreading, are interrupted, while the transverse memory circuits are spared. The extent of MHT is governed by intraoperative electrocorticography; abolition of epileptic discharges serves as an end point to terminate the transection. In other words, the aim of MHT is not the anatomical completeness of hippocampal transection. In contrast, we hypothesize that only the complete transection of hippocampal cross-section is needed to durably terminate epilepsy, avoiding possible postoperative reorganization of longitudinal pathways. Here, we report an anatomical study designed to evaluate the feasibility of complete transection of hippocampus with the aid of ultrasound neuronavigation and we propose new instruments to reach this goal. Five cadaveric brains were analyzed in this study. MHT was performed on both sides of each brain either with or without ultrasound neuronavigation. The percentage of transected cross-section of the hippocampus was measured using magnetic resonance imaging (MRI) and both sides were compared. The ultrasound-guided MHTs were more likely to achieve complete hippocampal transection compared with the nonnavigated MHT transection (73 vs 58%; p < 0.01). Our study also allowed us to propose specialized transectors to minimize invasivity of this procedure. Completeness of MHT can be better reached with the aid of an ultrasound neuronavigation system; modified instruments for this procedure were also designed.

Clinical characteristics and surgical outcomes of low-grade epilepsy-associated brain tumors

Background: Low-grade epilepsy-associated brain tumors (LEATs) are found to be the second most common lesion-related epilepsy. Malignant potential of LEATs is very low and the overall survival is good, so the focus of treatment is focused more on seizure outcome rather than oncological prognosis. Objectives: This study was conducted to evaluate the risk factors of seizure outcomes after resection in patients with LEATs. Design: A retrospective study. Methods: A retrospective analysis of patients with LEATs who underwent resective surgery in our three epilepsy centers between October 2010 and April 2023 with a minimum follow-up of 1 year. Demography, clinical characters, neurophysiology, and molecular neuropathology were assessed for association with postoperative seizure outcomes at 1-, 2-, and 5-year follow-up. Synthetic minority oversampling technique (SMOTE) algorithm model was performed to handle the imbalance of data distribution. Gaussian Naïve Bayes (GNB) algorithms were created as a basis for classifying outcomes according to observation indicators. Results: A total of 111 patients were enrolled in the cohort. The most common pathology was ganglioglioma ( n = 37, 33.3%). The percentage of patients with seizure freedom was 91.0% (101/111) at 1-year follow-up, 87.5% (77/88) at 2-year follow-up, and 79.1% (53/67) at 5-year follow-up. Partial resection had a significantly poor seizure outcome compared to total resection and supratotal resection ( p &lt; 0.05). The epileptiform discharge on post-resective intraoperative electrocorticography (ECoG) or postoperative scalp electroencephalography (EEG) were negative factors on postoperative seizure freedom at 1-, 2-, or 5-year follow-ups ( p &lt; 0.05). The area under the receiver-operating characteristic curve value of the GNB-SMOTE model was 0.95 (95% CI, 0.876–1.000), 0.892 (95% CI, 0.656–0.934), and 0.786 (95% CI, 0.491–0.937) at 1-, 2-, and 5-year follow-up, respectively. Conclusion: The partial resection, post-resective intraoperative ECoG, and postoperative scalp EEG were valuable indicators of poor seizure outcomes. The utilization of post-resective intraoperative ECoG is beneficial to improve seizure outcomes. Based on the data diversity and completeness of three medical centers, a multivariate correlation analysis model was established based on GNB algorithm.

KRM–II–81 suppresses epileptifom activity across the neural network of cortical tissue from a patient with pharmacoresistant epilepsy

A clinical case of a 19-year-old male patient with pharmacoresistant seizures occurring following parieto-occipital tumor-resection at age 6 is described. Seizure surgery work-up included prolonged video EEG monitoring and head CT without contrast. Seizure focus was localized to the left temporal lobe, and we felt that the patient was an excellent candidate for seizure surgery. The patient underwent a left frontotemporal craniotomy for removal of the seizure focus with intraoperative electrocorticography (ECoG) conducted pre and post resection. ECoG recordings pre- and post-resection confirmed resolution of seizure generation. Imaging obtained immediately postoperatively showed complete resection of the residual tumor with no evidence of recurrence in follow-ups. A year after the surgery the patient is seizure-free but remains on seizure medication. With the patient's consent the excised epileptogenic tissue was used for ex-vivo research studies. The microelectrode recordings confirmed epileptiform activity in the excised tissue incubated in excitatory artificial cerebrospinal fluid. The epileptiform activity in the epileptogenic tissue was suppressed by addition of KRM–II–81, a novel α2/3 subtype preferring GABAA receptor (GABAAR) potentiator with previously demonstrated antiepileptic efficacy in multiple animal models of epilepsy and with reduced potential for CNS side-effects compared to classical benzodiazepine GABAAR potentiators. These findings support the proposition that KRM–II–81 might reduce seizure burden in pharmacoresistant patients.

Can we improve electrocorticography using a circular grid array in brain tumor surgery?

Intraoperative electrocorticography (iECoG) is used as an adjunct to localize the epileptogenic zone during surgical resection of brain tumors in patients with focal epilepsies. It also enables monitoring of after-discharges and seizures with EEG during functional brain mapping with electrical stimulation. When seizures or after-discharges are present, they complicate accurate interpretation of the mapping strategy to outline the brain’s eloquent function and can affect the surgical procedure. Recurrent seizures during surgery requires urgent treatment and, when occurring during awake craniotomy, often leads to premature termination of brain mapping due to post-ictal confusion or sedation from acute rescue therapy. There are mixed results in studies on efficacy with iECoG in patients with epilepsy and brain tumors influencing survival and functional outcomes following surgery. Commercially available electrode arrays have inherent limitations. These could be improved with customization potentially leading to greater precision in safe and maximal resection of brain tumors. Few studies have assessed customized electrode grid designs as an alternative to commercially available products. Higher density electrode grids with intercontact distances less than 1 cm improve spatial delineation of electrophysiologic sources, including epileptiform activity, electrographic seizures, and afterdischarges on iECoG during functional brain mapping. In response to the shortcomings of current iECoG grid technologies, we designed and developed a novel higher-density hollow circular electrode grid array. The 360-degree iECoG monitoring capability allows continuous EEG recording during surgical intervention through the aperture with and without electrical stimulation mapping. Compared with linear strip electrodes that are commonly used for iECoG during surgery, the circular grid demonstrates significant benefits in brain tumor surgery. This includes quicker recovery of post-operative motor deficits (2.4 days versus 9 days, p = 0.05), more extensive tumor resection (92.0% versus 77.6%, p = 0.003), lesser reduction in Karnofsky Performance scale postoperatively (−2 versus −11.6, p = 0.007), and more sensitivity to recording afterdischarges. In this narrative review, we discuss the advantages and disadvantages of commercially available recording devices in the operating room and focus on the usefulness of the higher-density circular grid.

Localized focal cortical dysplasia type II: seizure freedom with lesionectomy guided by MRI and FDG-PET.

The authors perform thorough, noninvasive presurgical evaluations for intractable epilepsy at their center and avoid unnecessary intracranial EEG when possible. The purpose of this study was to clarify the appropriateness of their lesion-oriented surgical strategy for localized focal cortical dysplasia (FCD) type II. Fifty-one patients with pathologically proven localized FCD type II who were followed for at least 1 year after surgery were included. Patients with FCD type II with lobar or multilobar distribution were excluded. The results of presurgical evaluations, including thin-slice 3-T MRI, FDG-PET, and ictal SPECT, as well as surgical procedures and postoperative seizure and functional outcomes, were examined retrospectively. MRI was positive in 46 (90%) of 51 patients, and FDG-PET revealed localized hypo- or hypermetabolism in 47 (92%) of 51 patients. Ictal SPECT revealed concordant hyperperfusion in 37 of 42 patients examined. Intracranial EEG was used in only 13 patients (25%), including 5 with negative MRI results and 4 with subtle MRI findings. Of the 15 patients with FCD in the vicinity of eloquent (sensorimotor and language) areas, intracranial EEG was used in 4. Lesionectomy was performed in all 51 patients. Intraoperative electrocorticography (ECoG) was performed in 8 patients, but the findings were not used to tailor the extent of resection. Postoperative seizure outcomes were Engel class I in 47 patients (92%) and Ia in 45 (88%). In the 15 patients with FCD in the vicinity of eloquent areas, 13 (87%) achieved a class I outcome. Predictive factors for favorable seizure outcome were complete resection of the MRI lesion (p = 0.006) and frontal lobe surgery (p = 0.012). Postoperative neurological deficits were noted in only 4 (27%) of 15 patients with FCD in the vicinity of eloquent areas. All 5 MRI-negative patients achieved an Engel class I outcome. In most of the patients with localized FCD type II, MRI and/or FDG-PET detected the localized abnormality. Lesionectomy without intracranial EEG led to seizure freedom in most cases. Even when lesions were in the vicinity of eloquent areas, seizure and functional outcomes were favorable. Intraoperative ECoG may thus be unnecessary. Complete resection of the lesion is essential for favorable seizure outcome in MRI-positive patients. In MRI-negative patients, surgery with intracranial EEG guided by FDG-PET provided seizure-free outcomes.

Risk factors for preoperative and postoperative seizures in patients with glioblastoma according to the 2021 World Health Organization classification.

To identify risk factors for developing glioblastoma (GBM) related preoperative (PRS) and postoperative seizures (POS). Also, we aimed to analyze the impact of PRS and POS on survival in a GBM cohort according to the revised 2021 WHO glioma classification. We performed a single-center retrospective cohort study of patients with GBM (according to the 2021 World Health Organization Classification) treated at Mayo Clinic Florida between January 2018 and July 2022. Seizures were stratified into preoperative seizures (PRS) and postoperative seizures (POS, >7 days after surgery). Associations between patients' characteristics and overall survival with PRS and POS were assessed. One hundred nineteen adults (mean =60.9 years), 49 (41.2%) females, were identified. The rates of PRS and POS in the cohort were 35.3% (n=42) and 37.8% (n=45), respectively. Patients with PRS were younger (p = 0.035) and were likely to undergo intraoperative electrocorticography. The incidence of PRS (p = 0.049) and POS (p<0.001) was lower among patients with tumors located in the occipital location. PRS increased the risk of POS after adjusting for age and sex (RR: 2.59, CI=1.44-4.65, p = 0.001). There was no association between PRS or POS and other patient-related factors, including several tumor molecular markers (TMMs) examined. PRS (p = 0.036), POS (p<0.001), and O6-Methylguanine-DNA Methyltransferase (MGMT) promotor methylation status (p = 0.032) were associated with longer survival time. PRS and POS are associated with non-occipital tumor location and longer survival time in patients with GBM. While younger ages predicted PRS, PRS predicted POS. Well-designed prospective studies with larger sample sizes are needed to clarify the influence of TMMs in the genesis of epileptic seizures in patients with GBM.

Effect of Sevoflurane Anesthesia on Intraoperative Spikes, High-Frequency Oscillations, and Phase-Amplitude Coupling in MRI-Normal Hippocampus.

The purpose of this study was to determine the effect of sevoflurane anesthesia on spikes, high-frequency oscillations (HFOs), and phase-amplitude coupling using a modulation index in MRI-normal hippocampus, with the aim of evaluating the utility of intraoperative electrocorticography in identifying the epileptogenic hippocampus during sevoflurane administration. Eleven patients with intractable temporal lobe epilepsy with a normal hippocampus on MRI underwent extra-operative electrocorticography evaluation. Patients were assigned to the Ictal (+) or Ictal (-) group depending on whether the parahippocampal gyrus was included in the seizure onset zone. Intraoperative electrocorticography was performed under 0.5 and 1.5 minimum alveolar concentration of sevoflurane. The rates of spikes, ripples, fast ripples (FRs), ripples on spikes, FRs on spikes, and MI HFO(3-4 Hz) were evaluated. During the intraoperative electrocorticography procedure, sevoflurane administration was found to significantly increase the rate of spikes, ripples on spikes, fast ripples on spikes, and MI HFO(3-4 Hz) in the Ictal (+) group (P < 0.01). By contrast, the Ictal (-) group exhibited a paradoxical increase in the rate of ripples and fast ripple (P < 0.05). Our findings indicate that the administration of sevoflurane during intraoperative electrocorticography in patients with MRI-normal hippocampus can lead to a dose-dependent enhancement of epileptic biomarkers (spikes, ripples on spikes, fast ripples on spikes, and MI (HFO 3-4)) in the epileptogenic hippocampus, while paradoxically increasing the rate of ripples and fast ripple in the nonepileptogenic hippocampus. These results have significant implications for the identification of the MRI-normal hippocampus that requires surgical intervention and preservation of the nonepileptogenic hippocampus.

Brief potentially ictal rhythmic discharges on intraoperative electrocorticography predict a good outcome of focal cortical dysplasia after surgical resection: a case report

BackgroundFocal cortical dysplasia (FCD) is a common cause of drug-resistant epilepsy. Electroencephalography (EEG) biomarkers that predict good postoperative outcomes are essential for identifying patients with focal epilepsies.Case presentationWe report the case of a 21-year-old female with seizure onset at the age of 9, characterized by left-hand dystonic posturing and impaired awareness, which evolved to bilateral tonic-clonic seizures, evaluated in a neurological referral center in Lima, Peru. During 6-h video-EEG, interictal EEG revealing focal brief potentially ictal rhythmic discharges (BIRDs) over the right frontal central region, lasting less than 10 s. The ictal features were characterized by low-voltage fast activity over the same area. Brain magnetic resonance imaging (MRI) demonstrated a focal lesion of focal cortical dysplasia type II in the right frontal lobe. The patient underwent a lesionectomy guided by electrocorticography, which showed continuous polyspikes. BIRDs showing a brief burst of spikes lasting longer than 0.5 s, were also identified on intraoperative electrocorticography (ECoG) and helped define the extent of resection. The patient obtained an Engel Outcome Class IA at 6 years of follow-up.ConclusionsThe atypical BIRDs on ECoG can be used as a prognostic biomarker for prolonged seizure-freedom outcome in patients with epilepsy. Additional reports are needed in developing countries with and without brain MRI lesions to advance outpatient presurgical evaluations despite limited resources.

Resective epilepsy surgery in a limited-resource settings: A cohort from a multi-disciplinary epilepsy team in a developing country.

Multidisciplinary pre-surgical evaluation is vital for epilepsy surgery decision and outcomes. Resective epilepsy surgery with assisted monitoring is currently a standard treatment for focal drug resistant epilepsy (DRE). In resource-limited countries, lack of epilepsy surgery center is a huge challenge. We presented and illustrated how to create a multidisciplinary protocol with resource-limited settings in a developing country and epilepsy surgery outcome using brain mapping and monitoring techniques for ensuring satisfactory resection. We created multicentric incomplete but complementary units covering all epilepsy-related sub-specialties and covering a wide geographical area in our country. Then, we conducted a prospective and multicentric study with low resource settings on patients with focal DRE, who underwent resective epilepsy surgery and were followed up for at least 12 months and were evaluated for postoperative seizure outcome and complications if present. Preoperative comprehensive clinical, neurophysiological, neuropsychological, and radiological evaluations were performed by multidisciplinary epilepsy team. Intraoperative brain mapping including awake craniotomy and direct stimulation techniques, neurophysiological monitoring, and electrocorticography was carried out during surgical resection. The study included 47 patients (18 females and 29 males) with mean age 20.4 ± 10.02 years. Twenty-two (46.8%) patients were temporal epilepsy while 25 (53.2%) were extra-temporal epilepsy. The epilepsy surgery outcome at the last follow up was Engel Class I (seizure free) in 35 (74.5%), Class II (almost seizure free) in 8 (17%), Class III (worthwhile improvement) in 3 (6.4%), and Class IV (no worthwhile improvement) in 1 patient (2.1%). With low resource settings and lack of single fully equipped epilepsy center, favorable outcomes after resective surgery in patients with focal DRE could be achieved using careful presurgical multidisciplinary selection, especially with using intraoperative brain mapping and electrocorticography techniques.

Surgical treatment of epilepsy - Initial experience from a comprehensive epilepsy program in coastal South India.

The objectives of this study were to share our initial experience with epilepsy surgery and provide an overview on the surgical treatments of epilepsies. This was a retrospective analysis of the demographics and clinical and investigative features of patients who underwent epilepsy surgery between January 2016 and August 2021. Postoperative seizure outcome was categorized according to modified Engel's classification, and the minimum period of follow-up was 1 year. The study group included 30 patients with an age ranging from 6 years to 45 years (mean: 22.28 years, median: 20 years) and a male: female ratio of 20:10. The epilepsy duration before surgery ranged from 3 years to 32 years (median: 7 years). Majority of our patients underwent resective surgeries (28/30 = 93.3%), and disconnection procedures were done in two patients. This included one functional hemispherotomy and one posterior quadrantic disconnection. Temporal lobe resective surgery was the most common procedure (16/30 = 53.3%), followed by eight frontal lobe and two parietal lobe surgeries. Among resective surgeries, majority were lesional surgeries and the pathologies included mesial temporal sclerosis (4), dysembryoplastic neuroepithelial tumor (8), ganglioglioma (6), cavernoma (4), focal cortical dysplasia (2), gliosis (1), and one case of hypothalamic hamartoma. Intraoperative electrocorticography was used in all cases for optimizing surgical resection/disconnection. Nearly two-thirds of our patients (66.6%) had an Engel's Class I outcome, five patients had Engel's Class II outcome, three patients had Class III outcome, and one patient did not have any worthwhile improvement. Temporal lobe surgery patients had a better seizure outcome compared to extratemporal surgeries (84% vs. 74%). Overall, complications were minimal and short lasting, and comprised meningitis in three patients (5.6%) and transient worsening of hemiparesis following hemispherotomy in two patients. There was no mortality or long-lasting major morbidity in our patients. In carefully selected patients with drug-resistant epilepsy, surgery offers an excellent chance of becoming seizure-free with significant improvement in overall quality of life. Majority of the common epilepsy surgery procedures can be performed through a multidisciplinary approach even in centers with limited resources.

Clinical characteristics associated with the development of preoperative and postoperative seizures in patients with glioblastoma (P3-1.002)

<h3>Objective:</h3> To determine the factors which predict the occurrence of preoperative seizures (PRS) and post-operative seizures (POS) among patients with glioblastoma (GBM). <h3>Background:</h3> Seizures have been well described in patients with GBM, albeit at a lower frequency than low grade gliomas. Although recent studies suggest epileptogenesis has more to do with genetic molecular markers in low grade glioma-related seizure, information on factors that influence the development of of GBM-related PRS and POS is lacking. <h3>Design/Methods:</h3> We performed a single-center retrospective cohort study of patients with GBM evaluated at Mayo Clinic Florida, between 2018 and 2022. Clinical factors including, tumor molecular markers, neurophysiological and imaging findings were analyzed according to the status of PRS and POS. <h3>Results:</h3> One hundred thirty-two adult patients (median age=61.5 years), 79 (59.85%) females) were included. The most common locations were the temporal (n=50, 42.02%) and frontal (n=47, 39.50%) lobes. All patients underwent GBM resection, with 17.1% undergoing total resection (n=22). Sixty-two patients (46.27%) underwent intra-operative electrocorticography during GBM resection. Isocitrate dehydrogenase 1 (IDH1) wildtype was present in 121 patients (90.3%), 61 patients had O⁶-methylguanine-DNA methyltransferase (<i>MGMT</i>)-methylated GBM (46.21%). Forty patients (33.9%) had PRS, and 39 patients (38.24%) had POS (median follow-up=17.27 months; IQR=10.6–30.1). IDH1 wildtype and MGMT methylation status were not associated with PRS or POS. Patients with PRS were younger (59 years vs. 64 years, <b><i>p=0.021</i></b>) and experienced a longer survival time (16.1 months vs. 8.3 months, <b><i>p=0.044</i></b>) compared to patients without PRS. Occipital lobe GBM was associated with a lower likelihood of PRS (<b><i>p=0.043</i></b>) and POS (<b><i>p=0.001</i></b>). <h3>Conclusions:</h3> PRS is associated with younger age and longer survival time. PRS and POS are less likely to occur with occipital lobe tumors. Further studies are needed to confirm our findings and elucidate the influence of other tumor molecular markers in the development of PRS and POS in patients with GBM. <b>Disclosure:</b> Dr. Sánchez Boluarte has nothing to disclose. Dr. Garcia has nothing to disclose. Dr. Gunasekera has nothing to disclose. Dr. Tatum has received personal compensation in the range of $10,000-$49,999 for serving as a Consultant for Bioserenity. Dr. Tatum has received personal compensation in the range of $500-$4,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for Elsevier. Dr. Tatum has received personal compensation in the range of $500-$4,999 for serving as an Expert Witness for Defense Law Firm on behalf of a patient with epilepsy with funds donated to the Epilepsy Foundation of America. The institution of Dr. Tatum has received research support from Esai. The institution of Dr. Tatum has received research support from Mayo Clinic. The institution of Dr. Tatum has received research support from Liva Nova. The institution of Dr. Tatum has received research support from Engage Pharmaceuticals. The institution of Dr. Tatum has received research support from Xenon. Dr. Tatum has received publishing royalties from a publication relating to health care. Dr. Tatum has received publishing royalties from a publication relating to health care. Dr. Sirven has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for UCB. Dr. Sirven has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Medtronic. Dr. Sirven has received personal compensation in the range of $5,000-$9,999 for serving as a Consultant for Neurelis. Dr. Sirven has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Medtronic. Dr. Sirven has received personal compensation in the range of $10,000-$49,999 for serving as an Editor, Associate Editor, or Editorial Advisory Board Member for AAN. Dr. Sirven has stock in Doximity. Dr. Sirven has received publishing royalties from a publication relating to health care. Dr. Sirven has a non-compensated relationship as a Host with WJCT Public Media/ NPR that is relevant to AAN interests or activities. Dr. Freund has nothing to disclose. The institution of Dr. Ritaccio has received research support from NIH. Dr. Ritaccio has received intellectual property interests from a discovery or technology relating to health care. Kaisorn Chaichana has nothing to disclose. Alfredo Quiñones-Hinojosa has nothing to disclose. Dr. Feyissa has nothing to disclose.

154 Comparison of Chronic and Intraoperative LFP and ECoG Recordings in Humans With Parkinson’s Disease

INTRODUCTION: Advances in implantable neurotechnologies have enabled chronic invasive long-term recordings of field potentials from depth leads or paddle-type electrocorticography (ECoG) leads. The relationship between these long-term recordings and those obtained acutely in the operating room has not been studied. METHODS: Human subjects (n=6) with movement disorders (Parkinson’s disease, dystonia) were permanently implanted with quadripolar DBS leads, and quadripolar ECoG leads over primary motor and sensory cortices, attached to a Medtronic Summit RC+S investigational device in the chest. Recordings were acquired intraoperatively using a NeuroOmega (Alpha Omega, Inc) recording system customized for research use. RC+S recordings were acquired between 1 and 345 days post implantation. The same processing pipeline was applied to both data sets, and average power spectra in canonical frequency bands (delta, theta, alpha, beta, gamma) were compared using rank sum tests within each subject. RESULTS: Power spectra show similar power law scaling phenomena between intraoperative and chronic recordings. Disease specific frequency band characteristics such as beta peaks could be seen in both chronic and intraoperative recordings, however, within subjects these were not always consistently seen. CONCLUSIONS: We present within-patient comparisons of signal characteristics (power spectra) of intraoperative recordings from a research grade recording system, with wirelessly streamed data from a chronic implantable device, using the same brain leads. Power spectra have similar characteristics between the intraoperative and long term recordings, however, there are distinct differences between the intraoperative and longer term clinic recordings, reinforcing the utility of tracking neural signals over time after the effects of lead insertion on the motor circuit have diminished.

210 Intra-Operative Electrocorticography (ECoG) for Lesional Epilepsy: A Randomized Controlled Trial (IO-ECoG Trial)

INTRODUCTION: Usage of Electrocorticography (ECoG) is not clearly established. Robust evidence doesnot exist to support its regular usage in Long term Epilepsy associated tumors (LEATs) which constitutes approximately 25-35% cases of drug resistant epilepsy. METHODS: Prospective randomized controlled trial, including all patients operated for drug resistant epilepsy with non-eloquent area LEATs. Patients were randomized into 2 groups namely Group I (without usage of ECoG) and Group II (with ECoG usage). Group II patients further underwent tailored resections if necessary, as per ECoG practice protocols. Surgical outcomes were evaluated for seizure outcome (Engel scale) and adverse event profile. RESULTS: Total of 38 patients operated for LEATs having drug resistant epilepsy were included in the study with mean age of 21.1 years (range 2-46 years). 18 patients belonged to Group I and 20 patients belonged to Group II with mean follow-up period of 11.02 months (range 3-22 months). 30% patients (n = 6) in Group II underwent extended resection based on rhythmic persistent post resection spikes. 90% of Group II patients had Engel score Ia during follow up compared to 77.7% of Group I with Engel score Ia (p = 0.302). In Group II, 85.7% patients with extended tailored resection had Engel score Ia compared to 83.8% cases without extended resection (p = 0.904). CONCLUSIONS: Though ECoGs role may have been established in focal cortical dysplasia, its utility in LEATs is limited. Our randomized study confirmed that there is no added benefit conferred by the use of ECoG in LEATS. Additional tailored resections aided by ECoG also did not yield seizure outcome benefits in LEATS.

Usefulness of Intraoperative Electrocorticography for the Localization of Epileptogenic Zones.

Intraoperative electrocorticography (iECoG) is widely performed to identify irritative zones in the cortex during brain surgery; however, several limitations (e.g., short recording times and the effects of general anesthesia) reduce its effectiveness. The present study aimed to evaluate the utility of iECoG for localizing epileptogenic zones. We compared the results of iECoG and chronic electrocorticography (cECoG) in 25 patients with refractory epilepsy. Subdural electrodes were implanted with iECoG under general anesthesia (2% sevoflurane). cECoG recordings were performed for 3-14 days. The distribution of iECoG spikes was compared with cECoG spike, seizure onset zone, and resection areas. The concordance patterns of each distribution were classified into four patterns: Group 1: No spike in iECoG, Group 2: concordant (2a: iECoG smaller, 2b: iECoG larger, Group 3: discordant >50%). The concordance rate of interictal spikes, seizure onset zones, and resection areas were 88.0% (Group 2a: 72.0%, Group 2b: 16.0%), 70.0% (Group 2a: 25.0%, Group 2b: 45.0%), and 81.0% (Group 2a: 42.9%, Group 2b: 38.1%), respectively. The resection of iECoG spike areas significantly correlated with good surgical outcomes. The indication and limitations of iECoG need to be realized, and the complementary use of iECoG and cECoG may enhance clinical utility.

Electrocorticography for the Evaluation of Focus Resection

Electrocorticography(ECoG)with intracranial electrodes has a higher spatial resolution and higher sensitivity than conventional electroencephagrahy. Chronic VIDEO-ECoG with subdural grid electrodes has been used to determine the resection border of epileptic focus, and to evaluate cortical function prior to resective surgery. Recording multiple seizures is necessary to determine whether they are the same as habitual seizures and whether they are reproducible, to allow subsequent identification of the seizure onset zone. It is also necessary to understand the ictal ECoG patterns of various seizure onsets. Recent advances in engineering technology have made wideband(0.01 Hz-600Hz)analysis possible. The resection of the area with the ictal DC shift and high frequency oscillation is reported to improve surgical outcome. Although the procedure of subdural grid insertion is technically easy, high rates of complications, such as infections and bleeding, have been reported. Intraoperative acute ECoG was used to validate the extent of resection area. Overall, intraoperative ECoG is greatly affected by anesthetics, and the interictal epileptic discharge should be evaluated carefully.