Decision-making in stereotactic epilepsy surgery

Functional mapping of movement and speech using task-based electrophysiological changes in stereoelectroencephalography

OBJECTIVE

Stereoelectroencephalography (SEEG) has become the predominant method for intracranial seizure localization. When imaging, semiology, and scalp EEG findings are not in full agreement or definitively localizing, implanted SEEG recordings are used to test candidate seizure onset zones (SOZs). Discovered SOZs may then be targeted for resection, laser ablation, or neurostimulation. If an SOZ is eloquent, resection and ablation are both contraindicated, so identifying functional representation is crucial for therapeutic decision-making. The authors present a novel functional brain mapping technique that utilizes task-based electrophysiological changes in SEEG during behavioral tasks and test this in pediatric and adult patients.

METHODS

SEEG was recorded in 20 patients with epilepsy who ranged in age from 6 to 39 years (12 female, 18 of 20 patients < 21 years of age) and underwent implanted monitoring to identify seizure onset. Each performed 1) visually cued simple repetitive movements of the hand, foot, or tongue while electromyography was recorded; and 2) simple picture-naming or verb-generation speech tasks while audio was recorded. Broadband changes in the power spectrum of the SEEG recording were compared between behavior and rest.

RESULTS

Electrophysiological functional mapping of movement and/or speech areas was completed in all 20 patients. Eloquent representation was identified in both cortex and white matter and generally corresponded to classically described functional anatomical organization as well as other clinical mapping results. Robust maps of brain activity were identified in healthy brain, regions of developmental or acquired structural abnormality, and SOZs.

CONCLUSIONS

Task-based electrophysiological mapping using broadband changes in the SEEG signal reliably identifies movement and speech representation in pediatric and adult epilepsy patients.

High-resolution multimodal profiling of human epileptic brain activity via explanted depth electrodes

The availability and integration of electrophysiological and molecular data from the living brain is critical in understanding and diagnosing complex human disease. Intracranial stereo electroencephalography (SEEG) electrodes used for identifying the seizure focus in patients with epilepsy could enable the integration of such multimodal data. Here, we report multimodal profiling of epileptic brain activity via explanted depth electrodes (MoPEDE), a method that recovers extensive protein-coding transcripts, including cell type markers, DNA methylation, and short variant profiles from explanted SEEG electrodes matched with electrophysiological and radiological data allowing for high-resolution reconstructions of brain structure and function. We found gene expression gradients that corresponded with the neurophysiology-assigned epileptogenicity index but also outlier molecular fingerprints in some electrodes, potentially indicating seizure generation or propagation zones not detected during electroclinical assessments. Additionally, we identified DNA methylation profiles indicative of transcriptionally permissive or restrictive chromatin states and SEEG-adherent differentially expressed and methylated genes not previously associated with epilepsy. Together, these findings validate that RNA profiles and genome-wide epigenetic data from explanted SEEG electrodes offer high-resolution surrogate molecular landscapes of brain activity. The MoPEDE approach has the potential to enhance diagnostic decisions and deepen our understanding of epileptogenic network processes in the human brain.

Implementation of a Novel Seizure Assessment Tool for Unified Seizure Evaluation Improves Nurse Response

ABSTRACT

BACKGROUND: Ictal and postictal testing is an essential aspect of clinical care when diagnosing and treating seizures. The epilepsy monitoring unit (EMU) has standard operating procedures for nursing care during and after seizure events, but there is limited interrater reliability. Streamlining ictal and postictal testing processes may enhance care consistency for patients in the EMU unit. The purpose of this study was to create an ictal and postictal seizure assessment tool that would increase the consistency of nursing assessment for EMU patients. METHODS: This prospective study had 4 phases: baseline assessment, instrument development, staff education, and field testing. During baseline assessment, an advanced practice provider and an epilepsy fellow graded nurse ictal and postictal assessment via survey questions. After instrument development, education, and implementation, the same survey was administered to determine if nursing consistency in assessing seizure events improved. The tool used in this study was created by a team of clinical experts to ensure consistency in the assessment of seizure patients. RESULTS: A total of 58 first seizure events were collected over a 6-month intervention period; 27 in the pretest and 31 in the posttest. Paired t test analyses revealed significant improvement in the clinical testing domains of verbal language function ( P < .005), motor function ( P < .0005), and item assessment order ( P < .005) postintervention. There was nonsignificant improvement in the domains of responsiveness (feeling [ P = .597], using a code word [ P = .093]) and visual language function ( P = .602). CONCLUSION: The data captured in this study support the need for this instrument. There is strong need to increase consistency in assessing seizure events and to promote continued collaboration among clinical teams to enhance care to EMU patients. Validation of this instrument will further improve team collaboration by allowing nurses to contribute to their fullest extent.

Cognitive outcomes after magnetic resonance-guided laser interstitial thermal therapy for mesial temporal lobe epilepsy in adolescent patients

Surgical treatment of medication-resistant mesial temporal lobe epilepsy (MTLE) is associated with cognitive deficits. Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) for MTLE has been shown to result in superior cognitive outcomes in adults when compared to open surgical resection. However, data regarding postoperative cognitive outcomes in adolescent and pediatric patients is limited. We retrospectively reviewed sequential cases of pediatric patients who underwent MRgLITT for MTLE between 2017 and 2023. Patients who had complete preoperative and 12 month postoperative neuropsychological evaluation were analyzed for changes in the neuropsychological domains of cognition, memory, executive functioning, visual scanning, graphomotor speed, and fine motor speed/dexterity. Six adolescent patients who underwent MRgLITT for MTLE (x̄ age = 19.0 years, SD = 1.2) and had complete preoperative and postoperative neuropsychological evaluations were included in the analysis. There were no statistically significant changes across neuropsychological domains when comparing pre- and postoperative cognitive evaluations, including verbal memory scores. Clinically significant changes in phonemic fluency were observed when examining side-specific effects and improved for patients who received right-sided MRgLITT but declined for patients who received left-sided MRgLITT. 50 % of patients achieved Engel I outcome at last follow-up. Our preliminary results suggest minimal adverse neuropsychologic effects following MRgLITT for adolescent MTLE, including preservation of verbal memory. Clinical outcomes were similar with those reported in the literature.

Cell therapy for neurological disorders

Cell therapies for neurological disorders are entering the clinic and present unique challenges and opportunities compared with conventional medicines. They have the potential to replace damaged nervous tissue and integrate into the brain or spinal cord to produce functional effects for the lifetime of the patient, which could revolutionize the way clinicians treat debilitating neurological disorders. The major challenge has been cell sourcing, which historically relied mainly on fetal brain tissue. This has largely been overcome with the advent of pluripotent stem cell technology and the ability to make almost any cell of the nervous system at scale. Furthermore, advances in gene editing now allow the generation of genetically modified cells that could perform better and evade the immune system. With all the remarkable new approaches to treat neurological disorders, we take a critical look at the state of current clinical trials and how challenges may be overcome with the evolving technology and innovation occurring in the stem cell field.

A Standardized Approach to MRI-Guided Stereotactic Laser Corpus Callosotomy: Technical Description and Pediatric Case Series

BACKGROUND AND OBJECTIVES

Corpus callosotomy is an effective procedure approach for treating medication-resistant drop seizures, which pose a significant challenge in patients with epilepsy. Laser interstitial thermal therapy offers an alternative to open surgery for performing corpus callosotomy that may limit approach-related comorbidities. Practices vary regarding the number of laser filaments used and staging; outcome data for pediatric patients remain relatively limited.

METHODS

We illustrate a set of 4 standardized trajectories for performing MRI-guided stereotactic laser corpus callosotomy (SLCC). For this retrospective cohort study in a pediatric neurosurgery practice, the medical records and imaging were reviewed for 10 consecutive patients who had medication-refractory drop seizures and underwent SLCC. Data collected and analyzed included patient and epilepsy characteristics, procedural details, surgical approaches, and clinical follow-up results.

RESULTS

Over 2 years, complete, single-stage SLCC was performed in 8 patients, and posterior completion SLCC was performed in 2 patients who had previously had open anterior corpus callosotomy. Four laser fibers were used in four-eighth complete SLCC, and 3 fibers were used in four-eighth complete SLCC. Seven of 10 patients were discharged from the hospital on postoperative day 1, with only 1 requiring a maximum stay of 6 days. Five of 9 evaluable patients reported no drop seizures at the last clinical follow-up. In the other 4 patients, 1 experienced them only rarely, another experienced less than 25% preoperative frequency, and the remaining 2 had less than a 50% improvement. In addition, improvement in other seizure types exceeded 50% in 8 of 9 patients. Notably, no perioperative or postoperative complications were observed, nor were there any sustained neurological deficits reported.

CONCLUSION

Complete SLCC can be safely and effectively performed in pediatric patients. It is comparable in effectiveness with open surgery but has lower complication rates and shorter hospitalization.

The changing landscape of electrical stimulation language mapping with subdural electrodes and stereoelectroencephalography for pediatric epilepsy: A literature review and commentary

Electrical stimulation mapping (ESM) is used to locate the brain areas supporting language directly within the human cortex to minimize the risk of functional decline following epilepsy surgery. ESM is completed by utilizing subdural grid or depth electrodes (stereo-electroencephalography [sEEG]) in combination with behavioral evaluation of language. Despite technological advances, there is no standardized method of assessing language during pediatric ESM. To identify current clinical practices for pediatric ESM of language, we surveyed neuropsychologists in the Pediatric Epilepsy Research Consortium. Results indicated that sEEG is used for functional mapping at >80% of participating epilepsy surgery centers (n = 13/16) in the United States. However, >65% of sites did not report a standardized protocol to map language. Survey results indicated a clear need for practice recommendations regarding ESM of language. We then utilized PubMed/Medline and PsychInfo to identify 42 articles that reported on ESM of language, of which 18 met inclusion criteria, which included use of ESM/signal recording to localize language regions in children (<21 years) and a detailed account of the procedure and language measures used, and region-specific language localization outcomes. Articles were grouped based on the language domain assessed, language measures used, and the brain regions involved. Our review revealed the need for evidence-based clinical guidelines for pediatric language paradigms during ESM and a standardized language mapping protocol as well as standardized reporting of brain regions in research. Relevant limitations and future directions are discussed with a focus on considerations for pediatric language mapping.

Neuronal synchrony and critical bistability: Mechanistic biomarkers for localizing the epileptogenic network

OBJECTIVE

Postsurgical seizure freedom in drug-resistant epilepsy (DRE) patients varies from 30% to 80%, implying that in many cases the current approaches fail to fully map the epileptogenic zone (EZ). We aimed to advance a novel approach to better characterize epileptogenicity and investigate whether the EZ encompasses a broader epileptogenic network (EpiNet) beyond the seizure zone (SZ) that exhibits seizure activity.

METHODS

We first used computational modeling to test putative complex systems-driven and systems neuroscience-driven mechanistic biomarkers for epileptogenicity. We then used these biomarkers to extract features from resting-state stereoelectroencephalograms recorded from DRE patients and trained supervised classifiers to localize the SZ against gold standard clinical localization. To further explore the prevalence of pathological features in an extended brain network outside of the clinically identified SZ, we also used unsupervised classification.

RESULTS

Supervised SZ classification trained on individual features achieved accuracies of .6-.7 area under the receiver operating characteristic curve (AUC). Combining all criticality and synchrony features further improved the AUC to .85. Unsupervised classification discovered an EpiNet-like cluster of brain regions, in which 51% of brain regions were outside of the SZ. Brain regions in the EpiNet-like cluster engaged in interareal hypersynchrony and locally exhibited high-amplitude bistability and excessive inhibition, which was strikingly similar to the high seizure risk regime revealed by our computational modeling.

SIGNIFICANCE

The finding that combining biomarkers improves SZ localization accuracy indicates that the novel mechanistic biomarkers for epileptogenicity employed here yield synergistic information. On the other hand, the discovery of SZ-like brain dynamics outside of the clinically defined SZ provides empirical evidence of an extended pathophysiological EpiNet.

Feasibility, Safety, and Performance of Full-Head Subscalp EEG Using Minimally Invasive Electrode Implantation

BACKGROUND AND OBJECTIVES

Current practice in clinical neurophysiology is limited to short recordings with conventional EEG (days) that fail to capture a range of brain (dys)functions at longer timescales (months). The future ability to optimally manage chronic brain disorders, such as epilepsy, hinges upon finding methods to monitor electrical brain activity in daily life. We developed a device for full-head subscalp EEG (Epios) and tested here the feasibility to safely insert the electrode leads beneath the scalp by a minimally invasive technique (primary outcome). As secondary outcome, we verified the noninferiority of subscalp EEG in measuring physiologic brain oscillations and pathologic discharges compared with scalp EEG, the established standard of care.

METHODS

Eight participants with pharmacoresistant epilepsy undergoing intracranial EEG received in the same surgery subscalp electrodes tunneled between the scalp and the skull with custom-made tools. Postoperative safety was monitored on an inpatient ward for up to 9 days. Sleep-wake, ictal, and interictal EEG signals from subscalp, scalp, and intracranial electrodes were compared quantitatively using windowed multitaper transforms and spectral coherence. Noninferiority was tested for pairs of neighboring subscalp and scalp electrodes with a Bland-Altman analysis for measurement bias and calculation of the interclass correlation coefficient (ICC).

RESULTS

As primary outcome, up to 28 subscalp electrodes could be safely placed over the entire head through 1-cm scalp incisions in a ∼1-hour procedure. Five of 10 observed perioperative adverse events were linked to the investigational procedure, but none were serious, and all resolved. As a secondary outcome, subscalp electrodes advantageously recorded EEG percutaneously without requiring any maintenance and were noninferior to scalp electrodes for measuring (1) variably strong, stage-specific brain oscillations (alpha in wake, delta, sigma, and beta in sleep) and (2) interictal spikes peak-potentials and ictal signals coherent with seizure propagation in different brain regions (ICC >0.8 and absence of bias).

DISCUSSION

Recording full-head subscalp EEG for localization and monitoring purposes is feasible up to 9 days in humans using minimally invasive techniques and noninferior to the current standard of care. A longer prospective ambulatory study of the full system will be necessary to establish the safety and utility of this innovative approach.

TRIAL REGISTRATION INFORMATION

clinicaltrials.gov/study/NCT04796597.

Heart rate variability as a preictal marker for determining the laterality of seizure onset zone in frontal lobe epilepsy

Determining the laterality of the seizure onset zone is challenging in frontal lobe epilepsy (FLE) due to the rapid propagation of epileptic discharges to the contralateral hemisphere. There is hemispheric lateralization of autonomic control, and heart rate is modulated by interactions between the sympathetic and parasympathetic nervous systems. Based on this notion, the laterality of seizure foci in FLE might be determined using heart rate variability (HRV) parameters. We explored preictal markers for differentiating the laterality of seizure foci in FLE using HRV parameters. Twelve patients with FLE (6 right FLE and 6 left FLE) were included in the analyzes. A total of 551 (460 left FLE and 91 right FLE) 1-min epoch electrocardiography data were used for HRV analysis. We found that most HRV parameters differed between the left and right FLE groups. Among the machine learning algorithms applied in this study, the light gradient boosting machine was the most accurate, with an AUC value of 0.983 and a classification accuracy of 0.961. Our findings suggest that HRV parameter-based laterality determination models can be convenient and effective tools in clinical settings. Considering that heart rate can be easily measured in real time with a wearable device, our proposed method can be applied to a closed-loop device as a real-time monitoring tool for determining the side of stimulation.

Functional Mapping of Movement and Speech Using Task-Based Electrophysiological Changes in Stereoelectroencephalography

Introduction

Stereoelectroencephalography (sEEG) has become the predominant method for intracranial seizure localization. When imaging, semiology, and scalp EEG are not in full agreement or definitively localizing, implanted sEEG recordings are used to test candidate seizure onset zones (SOZs). Discovered SOZs may then be targeted for resection, laser ablation, or neurostimulation. If a SOZ is eloquent, resection and ablation are both contraindicated, so identifying functional representation is crucial for therapeutic decision making.

Objective

We present a novel functional brain mapping technique that utilizes task-based electrophysiological changes in sEEG during behavioral tasks and test this in pediatric and adult patients.

Methods

sEEG was recorded in twenty patients with epilepsy, aged 6-39 (12 female, 18 of 20 patients < 21 years old), who underwent implanted monitoring to identify seizure onset. Each performed 1) visually cued simple repetitive movements of the hand, foot, or tongue while electromyography was recorded, and 2) simple picture naming or verb generation speech tasks while audio was recorded. Broadband changes in the power spectrum of the sEEG were compared between behavior and rest.

Results

Electrophysiological functional mapping of movement and/or speech areas was completed in all 20 patients. Eloquent representation was identified in both cortex and white matter, and generally corresponded to classically described functional anatomic organization as well as other clinical mapping results. Robust maps of brain activity were identified in healthy brain, regions of developmental or acquired structural abnormality, and SOZs.

Conclusion

Task based electrophysiological mapping using broadband changes in the sEEG signal reliably identifies movement and speech representation in pediatric and adult epilepsy patients.

Laser interstitial thermal therapy in pediatric cerebellar epilepsy

Cerebellar lesional epilepsy is rare, commonly manifesting in early life and posing diagnostic and treatment challenges. Seizure semiology may be subtle, with repetitive eye blinking, face twitching, and irregular breathing, while EEG commonly remains unremarkable. Pharmacoresistance is the rule, and surgical intervention is the only treatment with the potential for cure. Novel minimally invasive techniques, such as laser interstitial thermal therapy (LITT), are emerging for surgically less accessible, deep-seated epileptogenic lesions. We report the case of a patient who presented with peculiar eye and face movements occurring episodically and stereotypically since the first weeks of life and was later diagnosed with cerebellar epilepsy related to a hamartoma. Refractory daily seizures, unresponsive to antiseizure medication, were followed by increasingly prominent gait ataxia and delayed speech development. Staged LITT was performed in two consecutive sessions at 3 and 4 years, leading to seizure cessation, neurological improvement, and developmental gains over a postsurgical follow-up period of 8 months. Our case highlights cerebellar lesional epilepsy as a rare but important differential diagnosis in children with paroxysmal disorders predominantly involving the face. Furthermore, we illustrate the radiological correlates of neurocognitive deficit related to the cerebellar lesion, manifesting as cerebello-cerebral diaschisis. Most importantly, our observations showcase LITT as a safe and effective therapeutic approach in cerebellar lesional epilepsy and an attractive alternative to open brain surgery, especially for deep-seated lesions in the pediatric population.

Implantation and reimplantation of intracranial EEG electrodes in patients considering epilepsy surgery

In patients with drug-resistant epilepsy who are considering surgery, intracranial EEG (iEEG) helps delineate the putative epileptogenic zone. In a minority of patients, iEEG fails to identify seizure onsets. In such cases, it might be worthwhile to reimplant more iEEG electrodes. The consequences of such a strategy for the patient are unknown. We matched 12 patients in whom the initially implanted iEEG electrodes did not delineate the seizure onset zone precisely enough to offer resective surgery, and in whom additional iEEG electrodes were implanted during the same inpatient stay, to controls who did not undergo reimplantation. Seven cases and eight controls proceeded to resective surgery. No intracranial infection occurred. One control suffered an intracranial hemorrhage. Three cases and two controls suffered from a post-operative neurological or neuropsychological deficit. We found no difference in post-operative seizure control between cases and controls. Compared to an ILAE score of 5 (ie, stable seizure frequency in the absence of resective surgery), cases showed significant improvement. Reimplantation of iEEG electrodes can offer the possibility of resective epilepsy surgery to patients in whom the initial iEEG investigation was inconclusive, without compromising on the risk of complications or seizure control.

A motor association area in the depths of the central sulcus

Cells in the precentral gyrus directly send signals to the periphery to generate movement and are principally organized as a topological map of the body. We find that movement-induced electrophysiological responses from depth electrodes extend this map three-dimensionally throughout the gyrus. Unexpectedly, this organization is interrupted by a previously undescribed motor association area in the depths of the midlateral aspect of the central sulcus. This 'Rolandic motor association' (RMA) area is active during movements of different body parts from both sides of the body and may be important for coordinating complex behaviors.

Canonical Response Parameterization: Quantifying the structure of responses to single-pulse intracranial electrical brain stimulation

Single-pulse electrical stimulation in the nervous system, often called cortico-cortical evoked potential (CCEP) measurement, is an important technique to understand how brain regions interact with one another. Voltages are measured from implanted electrodes in one brain area while stimulating another with brief current impulses separated by several seconds. Historically, researchers have tried to understand the significance of evoked voltage polyphasic deflections by visual inspection, but no general-purpose tool has emerged to understand their shapes or describe them mathematically. We describe and illustrate a new technique to parameterize brain stimulation data, where voltage response traces are projected into one another using a semi-normalized dot product. The length of timepoints from stimulation included in the dot product is varied to obtain a temporal profile of structural significance, and the peak of the profile uniquely identifies the duration of the response. Using linear kernel PCA, a canonical response shape is obtained over this duration, and then single-trial traces are parameterized as a projection of this canonical shape with a residual term. Such parameterization allows for dissimilar trace shapes from different brain areas to be directly compared by quantifying cross-projection magnitudes, response duration, canonical shape projection amplitudes, signal-to-noise ratios, explained variance, and statistical significance. Artifactual trials are automatically identified by outliers in sub-distributions of cross-projection magnitude, and rejected. This technique, which we call "Canonical Response Parameterization" (CRP) dramatically simplifies the study of CCEP shapes, and may also be applied in a wide range of other settings involving event-triggered data.

Laser Interstitial Thermal Therapy for Epilepsy

Laser interstitial thermal therapy is an important new technique with a diverse use in epilepsy. This article gives an up-to-date evaluation of the current use of the technique within epilepsy, as well as provides some guidance to novice users appropriate clinical cases for its use.

Letter to the Editor Regarding “Stereotactic biopsy and laser ablation of the ganglioglioma using a thulium laser: a video case report”

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