Increased nationwide use of stereoencephalography for intracranial epilepsy electroencephalography recordings

Systematic review of seizure-onset patterns in stereo-electroencephalography: Current state and future directions

OBJECTIVE

Increasing evidence suggests that the seizure-onset pattern (SOP) in stereo-electroencephalography (SEEG) is important for localizing the "true" seizure onset. Specifically, SOPs with low-voltage fast activity (LVFA) are associated with seizure-free outcome (Engel I). However, several classifications and various terms corresponding to the same pattern have been reported, challenging its use in clinical practice.

METHOD

Following the Preferred Reporting Items of Systematic reviews and Meta-Analyses (PRISMA) guideline, we performed a systematic review of studies describing SOPs along with accompanying figures depicting the reported SOP in SEEG.

RESULTS

Of 1799 studies, 22 met the selection criteria. Among the various SOPs, we observed that the terminology for low frequency periodic spikes exhibited the most variability, whereas LVFA is the most frequently used term of this pattern. Some SOP terms were inconsistent with standard EEG terminology. Finally, there was a significant but weak association between presence of LVFA and seizure-free outcome.

CONCLUSION

Divergent terms were used to describe the same SOPs and some of these terms showed inconsistencies with the standard EEG terminology. Additionally, our results confirmed the link between patterns with LVFA and seizure-free outcomes. However, this association was not strong.

SIGNIFICANCE

These results underline the need for standardization of SEEG terminology.

The United States Stereotactic EEG Survey: Current Practice and Future Opportunities

PURPOSE

Stereotactic EEG (SEEG) is being increasingly used in the intracranial evaluation of refractory epilepsy in the United States. A 2022 survey of SEEG practices among National Association of Epilepsy Centers tertiary referral (NAEC level IV) centers found largely similar practices across institutions. However, a few significant differences were noted in technical and patient care practice, and in the level of SEEG background training. In the year since publication, we review the identified challenges facing SEEG practice and suggest specific corrective action.

CONCLUSIONS

Stereotactic EEG has rapidly become the principal method for intracranial EEG monitoring in epilepsy surgery centers in the United States. The rate of adoption of SEEG is currently higher than the growth of invasive monitoring overall. Most report similar indications for SEEG, although significant variability exists in personnel expertise and technical and patient care practice. Consensus statements, guidelines, and review of postgraduate training curricula are urgently needed to benchmark SEEG practice and develop appropriate skillsets in the next generation of practitioners in the United States.

Voxeloc: A time-saving graphical user interface for localizing and visualizing stereo-EEG electrodes

BACKGROUND

Thanks to its unrivalled spatial and temporal resolutions and signal-to-noise ratio, intracranial EEG (iEEG) is becoming a valuable tool in neuroscience research. To attribute functional properties to cortical tissue, it is paramount to be able to determine precisely the localization of each electrode with respect to a patient's brain anatomy. Several software packages or pipelines offer the possibility to localize manually or semi-automatically iEEG electrodes. However, their reliability and ease of use may leave to be desired.

NEW METHOD

Voxeloc (voxel electrode locator) is a Matlab-based graphical user interface to localize and visualize stereo-EEG electrodes. Voxeloc adopts a semi-automated approach to determine the coordinates of each electrode contact, the user only needing to indicate the deep-most contact of each electrode shaft and another point more proximally.

RESULTS

With a deliberately streamlined functionality and intuitive graphical user interface, the main advantages of Voxeloc are ease of use and inter-user reliability. Additionally, oblique slices along the shaft of each electrode can be generated to facilitate the precise localization of each contact. Voxeloc is open-source software and is compatible with the open iEEG-BIDS (Brain Imaging Data Structure) format.

COMPARISON WITH EXISTING METHODS

Localizing full patients' iEEG implants was faster using Voxeloc than two comparable software packages, and the inter-user agreement was better.

CONCLUSIONS

Voxeloc offers an easy-to-use and reliable tool to localize and visualize stereo-EEG electrodes. This will contribute to democratizing neuroscience research using iEEG.

Real-time display of intracranial subdural electrodes and the brain surface during an electrode implantation procedure using permeable film

Background

Subdural electrode (SDE) implantation is an important method of diagnosing epileptogenic lesions and mapping brain function, even with the current preference for stereoelectroencephalography. We developed a novel method to assess SDEs and the brain surface during the electrode implantation procedure using brain images printed onto permeable films and intraoperative fluoroscopy. This method can help verify the location of the electrode during surgery and improve the accuracy of SDE implantation.

Methods

We performed preoperative imaging by magnetic resonance imaging and computed tomography. Subsequently, the images were edited and fused to visualize the gyrus and sulcus better. We printed the images on permeable films and superimposed them on the intraoperative fluoroscopy display. The intraoperative and postoperative coordinates of the electrodes were obtained after the implantation surgery, and the differences in the locations were calculated.

Results

Permeable films were created for a total of eight patients with intractable epilepsy. The median difference of the electrodes between the intraoperative and postoperative images was 4.6 mm (Interquartile range 2.9-7.1). The locations of electrodes implanted outside the operation field were not significantly different from those implanted inside.

Conclusion

Our new method may guide the implantation of SDEs into their planned location.

An automated algorithm for stereoelectroencephalography electrode localization and labelling

PURPOSE

Stereoelectroencephalography (sEEG) is increasingly utilized for localization of seizure foci, functional mapping, and neurocognitive research due to its ability to target deep and difficult to reach anatomical locations and to study in vivo brain function with a high signal-to-noise ratio. The research potential of sEEG is constrained by the need for accurate localization of the implanted electrodes in a common template space for group analyses.

METHODS

We present an algorithm to automate the grouping of sEEG electrodes by trajectories, labelled by target and insertion point. This algorithm forms the core of a pipeline that fully automates the entire process of electrode localization in standard space, using raw CT and MRI images to produce atlas labelled MNI coordinates.

RESULTS

Across 196 trajectories from 20 patients, the pipeline successfully processed 190 trajectories with localizations within 0.25±0.55 mm of the manual annotation by two reviewers. Six electrode trajectories were not directly identified due to metal artifacts and locations were interpolated based on the first and last contact location and the number of contacts in that electrode as listed in the surgical record.

CONCLUSION

We introduce our algorithm and pipeline for automatically localizing, grouping, and classifying sEEG electrodes from raw CT and MRI. Our algorithm adds to existing pipelines and toolboxes for electrode localization by automating the manual step of marking and grouping electrodes, thereby expedites the analyses of sEEG data, particularly in large datasets.

Safety of Concomitant Cortical and Thalamic Stereoencephalography Explorations in Patients With Drug-Resistant Epilepsies

BACKGROUND AND OBJECTIVES

Intracranial electrophysiology of thalamic nuclei has demonstrated involvement of thalamic areas in the propagation of seizures in focal drug-resistant epilepsy. Recent studies have argued that thalamus stereoencephalography (sEEG) may aid in understanding the epileptogenic zone and treatment options. However, the study of thalamic sEEG-associated hemorrhage incidence has not been investigated in a cohort study design. In this article, we present the largest retrospective cohort study of sEEG patients and compare hemorrhage rates between those with and without thalamic sEEG monitoring.

METHODS

Retrospective chart review of clinical and epilepsy history, electrode implantation, rationale, and outcomes was performed for 76 patients (age 20-69 years) with drug-resistant epilepsy who underwent sEEG monitoring at our institution (2019-2022). A subset of 38% of patients (n = 30) underwent thalamic monitoring of the anterior thalamic nucleus (n = 14), pulvinar nucleus (n = 25), or both (n = 10). Planned perisylvian orthogonal sEEG trajectories were extended to 2- to 3-cm intraparenchymally access thalamic area(s).The decision to incorporate thalamic monitoring was made by the multidisciplinary epilepsy team. Statistical comparison of hemorrhage rate, type, and severity between patients with and without thalamic sEEG monitoring was made.

RESULTS

Our approach for thalamic monitoring was not associated with local intraparenchymal hemorrhage of thalamic areas or found along extended cortical trajectories, and symptomatic hemorrhage rates were greater for patients with thalamic coverage (10% vs 0%, P = .056), although this was not found to be significant. Importantly, patients with perisylvian electrode trajectories, with or without thalamic coverage, did not experience a higher incidence of hemorrhage (P = .34).

CONCLUSION

sEEG of the thalamus is a safe and valuable tool that can be used to interrogate the efficacy of thalamic neuromodulation for drug-resistant epilepsy. While patients with thalamic sEEG did have higher incidence of hemorrhage at any monitoring site, this finding was apparently not related to the method of perisylvian implantation and did not involve any trajectories targeting the thalamus.

Retained Intracerebral Depth Electrode after Stereotactic Electroencephalography Monitoring: A Case Report

Stereotactic electroencephalography (SEEG) is an increasingly popular surgical modality for localizing the epileptogenic zone. Robot-guided stereotactic electrode placement has been covered in Japan by National Health Insurance since 2020. However, several surgical devices, such as the anchor bolt (a thin, hollow, metal shaft that serves as a guide screw or fixing for each electrode), have not been approved. A 14-year-old female who underwent SEEG for intractable epilepsy and required additional surgery to remove a retained depth electrode from the skull after the SEEG monitoring was finished. She had uncontrolled focal seizures consisting of nausea and laryngeal constriction at the onset. After a comprehensive presurgical evaluation, robot-guided stereotactic electrode implantation was performed to evaluate her seizures by SEEG. Nine depth electrodes were implanted through the twist drill hole. The electrodes were sutured to her skin for fixation without anchor bolts. When we attempted to remove the electrodes after 8 days of SEEG monitoring, one of the electrodes was retained. The retained electrode was removed through an additional skin incision and a small craniectomy under general anesthesia. We confirmed narrowing of the twist drill hole pathway in the internal table of the skull due to osteogenesis, which locked the electrode. This complication might be avoided if an anchor bolt had been used. This case report prompts the approval of the anchor bolts to avoid difficulty in electrode removal. Moreover, approval of a depth electrode with a thinner diameter and more consistent hardness is needed.

Trends in the Utilization of Surgical Modalities for the Treatment of Drug-Resistant Epilepsy: A Comprehensive 10-Year Analysis Using the National Inpatient Sample

BACKGROUND AND OBJECTIVES

Epilepsy is considered one of the most prevalent and severe chronic neurological disorders worldwide. Our study aims to analyze the national trends in different treatment modalities for individuals with drug-resistant epilepsy and investigate the outcomes associated with these procedural trends in the United States.

METHODS

Using the National Inpatient Sample database from 2010 to 2020, patients with drug-resistant focal epilepsy who underwent laser interstitial thermal therapy (LITT), open surgical resection, vagus nerve stimulation (VNS), or responsive neurostimulation (RNS) were identified. Trend analysis was performed using piecewise joinpoint regression. Propensity score matching was used to compare outcomes between 10 years prepandemic before 2020 and the first peak of the COVID-19 pandemic.

RESULTS

This study analyzed a total of 33 969 patients with a diagnosis of drug-resistant epilepsy, with 3343 patients receiving surgical resection (78%), VNS (8.21%), RNS (8%), and LITT (6%). Between 2010 and 2020, there was an increase in the use of invasive electroencephalography monitoring for seizure zone localization (P = .003). There was an increase in the use of LITT and RNS (P < .001), while the use of surgical resection and VNS decreased over time (P < .001). Most of these patients (89%) were treated during the pre-COVID pandemic era (2010-2019), while a minority (11%) underwent treatment during the COVID pandemic (2020). After propensity score matching, the rate of pulmonary complications, postprocedural hematoma formation, and mortality were slightly higher during the pandemic compared with the prepandemic period (P = .045, P = .033, and P = .026, respectively).

CONCLUSION

This study indicates a relative decrease in the use of surgical resections, as a treatment for drug-resistant focal epilepsy. By contrast, newer, minimally invasive surgical approaches including LITT and RNS showed gradual increases in usage.

Decision and response monitoring during working memory are sequentially represented in the human insula

Emerging research supports a role of the insula in human cognition. Here, we used intracranial EEG to investigate the spatiotemporal dynamics in the insula during a verbal working memory (vWM) task. We found robust effects for theta, beta, and high frequency activity (HFA) during probe presentation requiring a decision. Theta band activity showed differential involvement across left and right insulae while sequential HFA modulations were observed along the anteroposterior axis. HFA in anterior insula tracked decision making and subsequent HFA was observed in posterior insula after the behavioral response. Our results provide electrophysiological evidence of engagement of different insula subregions in both decision-making and response monitoring during vWM and expand our knowledge of the role of the insula in complex human behavior.

An international survey of SEEG cortical stimulation practices

OBJECTIVE

Cortical stimulation is an important component of stereoelectroencephalography (SEEG). Despite this, there is currently no standardized approach and significant heterogeneity in the literature regarding cortical stimulation practices. Via an international survey of SEEG clinicians, we sought to examine the spectrum of cortical stimulation practices to reveal areas of consensus and variability.

METHODS

A 68-item questionnaire was developed to understand cortical stimulation practices including neurostimulation parameters, interpretation of epileptogenicity, functional and cognitive assessment and subsequent surgical decisions. Multiple recruitment pathways were pursued, with the questionnaire distributed directly to 183 clinicians.

RESULTS

Responses were received from 56 clinicians across 17 countries with experience ranging from 2 to 60 years (M = 10.73, SD = 9.44). Neurostimulation parameters varied considerably, with maximum current ranging from 3 to 10 mA (M = 5.33, SD = 2.29) for 1 Hz and from 2 to 15 mA (M = 6.54, SD = 3.68) for 50 Hz stimulation. Charge density ranged from 8 to 200 μC/cm2 , with up to 43% of responders utilizing charge densities higher than recommended upper safety limits, i.e. 55 μC/cm2 . North American responders reported statistically significant higher maximum current (P < 0.001) for 1 Hz stimulation and lower pulse width for 1 and 50 Hz stimulation (P = 0.008, P < 0.001, respectively) compared to European responders. All clinicians evaluated language, speech, and motor function during cortical stimulation; in contrast, 42% assessed visuospatial or visual function, 29% memory, and 13% executive function. Striking differences were reported in approaches to assessment, classification of positive sites, and surgical decisions guided by cortical stimulation. Patterns of consistency were observed for interpretation of the localizing capacity of stimulated electroclinical seizures and auras, with habitual electroclinical seizures induced by 1 Hz stimulation considered the most localizing.

SIGNIFICANCE

SEEG cortical stimulation practices differed vastly across clinicians internationally, highlighting the need for consensus-based clinical guidelines. In particular, an internationally standardized approach to assessment, classification, and functional prognostication will provide a common clinical and research framework for optimizing outcomes for people with drug-resistant epilepsy.

Quantifying interictal intracranial EEG to predict focal epilepsy

Introduction

Intracranial EEG (IEEG) is used for 2 main purposes, to determine: (1) if epileptic networks are amenable to focal treatment and (2) where to intervene. Currently these questions are answered qualitatively and sometimes differently across centers. There is a need for objective, standardized methods to guide surgical decision making and to enable large scale data analysis across centers and prospective clinical trials.

Methods

We analyzed interictal data from 101 patients with drug resistant epilepsy who underwent presurgical evaluation with IEEG. We chose interictal data because of its potential to reduce the morbidity and cost associated with ictal recording. 65 patients had unifocal seizure onset on IEEG, and 36 were non-focal or multi-focal. We quantified the spatial dispersion of implanted electrodes and interictal IEEG abnormalities for each patient. We compared these measures against the "5 Sense Score (5SS)," a pre-implant estimate of the likelihood of focal seizure onset, and assessed their ability to predict the clinicians' choice of therapeutic intervention and the patient outcome.

Results

The spatial dispersion of IEEG electrodes predicted network focality with precision similar to the 5SS (AUC = 0.67), indicating that electrode placement accurately reflected pre-implant information. A cross-validated model combining the 5SS and the spatial dispersion of interictal IEEG abnormalities significantly improved this prediction (AUC = 0.79; p<0.05). The combined model predicted ultimate treatment strategy (surgery vs. device) with an AUC of 0.81 and post-surgical outcome at 2 years with an AUC of 0.70. The 5SS, interictal IEEG, and electrode placement were not correlated and provided complementary information.

Conclusions

Quantitative, interictal IEEG significantly improved upon pre-implant estimates of network focality and predicted treatment with precision approaching that of clinical experts. We present this study as an important step in building standardized, quantitative tools to guide epilepsy surgery.

Use of the Globus ExcelsiusGPS System for Robotic Stereoelectroencephalography: An Initial Experience

BACKGROUND

Stereoelectroencephalography (SEEG) is a critical tool used in the identification of epileptogenic zones. Although stereotactic frame-based SEEG procedures have been performed traditionally, newer robotic-assisted SEEG procedures have become increasingly common. In this study, we evaluate the accuracy, efficacy of the ExcelsiusGPS robot (Globus Medica, Audubon, PA) in SEEG procedures.

METHODS

Five consecutive adult patients with drug resistant epilepsy were identified as SEEG candidates via a multidisciplinary epilepsy surgery committee. Preoperative scans were merged onto the robot to plan electrode placement. With the use of a camera system, dynamic reference base, and surveillance markers, the robotic arm was used to establish the trajectory of the electrodes. Postoperative computed tomography (CT) scans were merged onto the preoperatively planned trajectory and the radial, depth, and entry errors were calculated. Fiducial registration error was calculated for 4 cases to determine error between the patient and intraoperative CT merge.

RESULTS

A total of 59 electrodes were placed. The mean age at surgery was 41.6 ± 15.1 years. Mean operating room time, anesthesia time, and surgical time was 301.6 ± 44.4 min, 261.6 ± 50.2 min, and 155.8 ± 48.8 min, respectively. The overall mean depth, radial, and entry errors were 2.5 ± 1.9 mm, 1.9 ± 1.5 mm, and 1.6 ± 1.2 mm. Mean fiducial registration error retrospectively calculated for 4 of 5 cases was 0.13 ± 0.04 mm. There were no perioperative complications.

CONCLUSIONS

The initial performance of the ExcelsiusGPS robotic system yielded comparable results to other systems currently in use for adult SEEG procedures.

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.

Trans-Interhemispheric Stereoelectroencephalography Depth Electrode Placement for Mesial Frontal Lobe Explorations in Medically Refractory Epilepsy: A Technical Note and Case Series

BACKGROUND

Stereoelectroencephalography (SEEG) is an established and safe methodology for extra-operative invasive monitoring in patients with medical refractory epilepsy. SEEG has several advantages such as the ability to record deep cortical structures, mapping the epileptogenic zone in a three-dimensional manner, and analyze bihemispheric regions without the need for bilateral craniotomies. In patients with bilateral hemispheric hypotheses, especially the mesial surface of frontal lobes, bilateral lead placement is compulsory to further define and localize the epileptogenic zone. In this particular cohort of patients, bilateral monitoring may be accomplished from a single entry point using trans-interhemispheric placement of the electrodes. The use of trans-interhemispheric monitoring offers several advantages including sparing the need for additional leads.

OBJECTIVE

To test the hypothesis that, given the lack of the falx as a limiting structure in the ventral and mesial frontal lobe regions, trans-interhemispheric SEEG placement is feasible and a potential benefit for the SEEG method.

METHODS

We report on 6 patients who underwent bilateral monitoring using trans-interhemispheric SEEG lead placement and discuss the operative technique.

RESULTS

Six patients underwent trans-interhemispheric monitoring, with a median of 3 leads per patient (19 total). Trajectory error was minimal (<0.3 mm), and operating room time was comparable with that in previous reports. All leads were placed without adverse events, mislocalization, electrode hemorrhages, or any other complications. All patients had successful localization of the epileptogenic zone.

CONCLUSION

Trans-interhemispheric SEEG to monitor the mesial wall of frontal lobe regions is technically feasible. No adverse events were observed, suggesting a favorable safety profile.

Modern intracranial electroencephalography for epilepsy localization with combined subdural grid and depth electrodes with low and improved hemorrhagic complication rates

OBJECTIVE

Recent trends have moved from subdural grid electrocorticography (ECoG) recordings toward stereo-electroencephalography (SEEG) depth electrodes for intracranial localization of seizures, in part because of perceived morbidity from subdural grid and strip electrodes. For invasive epilepsy monitoring, the authors describe the outcomes of a hybrid approach, whereby patients receive a combination of subdural grids, strips, and frameless stereotactic depth electrode implantations through a craniotomy. Evolution of surgical techniques was employed to reduce complications. In this study, the authors review the surgical hemorrhage and functional outcomes of this hybrid approach.

METHODS

A retrospective review was performed of consecutive patients who underwent hybrid implantation from July 2012 to May 2022 at an academic epilepsy center by a single surgeon. Outcomes included hemorrhagic and nonhemorrhagic complications, neurological deficits, length of monitoring, and number of electrodes.

RESULTS

A total of 137 consecutive procedures were performed; 113 procedures included both subdural and depth electrodes. The number of depth electrodes and electrode contacts did not increase the risk of hemorrhage. A mean of 1.9 ± 0.8 grid, 4.9 ± 2.1 strip, and 3.0 ± 1.9 depth electrodes were implanted, for a mean of 125.1 ± 32 electrode contacts per patient. The overall incidence of hematomas over the study period was 5.1% (7 patients) and decreased significantly with experience and the introduction of new surgical techniques. The incidence of hematomas in the last 4 years of the study period was 0% (55 patients). Symptomatic hematomas were all delayed and extra-axial. These patients required surgical evacuation, and there were no cases of hematoma recurrence. All neurological deficits related to hematomas were temporary and were resolved at hospital discharge. There were 2 nonhemorrhagic complications. The mean duration of monitoring was 7.3 ± 3.2 days. Seizures were localized in 95% of patients, with 77% of patients eventually undergoing resection and 17% undergoing responsive neurostimulation device implantation.

CONCLUSIONS

In the authors' institutional experience, craniotomy-based subdural and depth electrode implantation was associated with low hemorrhage rates and no permanent morbidity. The rate of hemorrhage can be nearly eliminated with surgical experience and specific techniques. The decision to use subdural electrodes or SEEG should be tailored to the patient's unique pathology and surgeon experience.

Health care resource utilization and costs before and after epilepsy surgery

OBJECTIVE

To describe the demographics of epilepsy surgery utilization and its impact on health care resource use.

METHODS

Retrospective descriptive study using the MarketScan commercial claims database. We studied children and adults who underwent epilepsy surgery in the USA in the period 2006-2019. Our main outcome was health care resource utilization.

RESULTS

Among the 87,368 patients with refractory epilepsy, 2,011 (2.3%) patients underwent resective epilepsy surgery, 188 (0.2%) patients underwent partial or total hemispherectomy, and 183 (0.2%) patients underwent corpus callosotomy. The proportion of patients undergoing epilepsy surgery has barely increased in the period 2006 to 2019. The year of resective epilepsy surgery was associated with high healthcare costs per person-year [median (p₂₅-p₇₅): $140,322 ($88,749-$225,862)], but healthcare costs per person-year substantially decreased in the 5 years after compared to the 5 years before the year of resective epilepsy surgery [$7,691 ($2,738-$22,092) versus $18,750 ($7,361-$47,082), p-value < 0.0001]. This result held in all resective epilepsy surgery subgroups: children, adults, temporal, extratemporal, subdural EEG monitoring, stereoEEG monitoring, and no intracranial monitoring. Similarly, the year of hemispherectomy was associated with high healthcare costs per person-year [$260,983 ($154,791-$453,986)], but healthcare costs per person-year substantially decreased in the 5 years after compared to the 5 years before the year of hemispherectomy [$26,834 ($12,842-$52,627) versus $54,596 ($19,547-$136,412), p-value < 0.0001]. In contrast, the year of corpus callosotomy was associated with high healthcare costs per person-year [$162,399 ($108,150-$253,156)], but healthcare costs per person-year did not substantially decrease in the 5 years after than in the 5 years before the year of corpus callosotomy [$25,464 ($10,764-$69,338) versus $36,221 ($12,841-$85,747), p-value = 0.2142].

CONCLUSION

In privately insured patients in the USA, resective epilepsy surgery and hemispherectomy substantially decrease healthcare utilization in subsequent years. Epilepsy surgery may help contain costs in the field of epilepsy.

Cost-effectiveness of invasive monitoring strategies in epilepsy surgery

OBJECTIVE

Drug-resistant epilepsy occurs in up to 40% of patients with epilepsy who may be considered for epilepsy surgery. For drug-resistant focal epilepsy, up to 50% of patients require invasive monitoring prior to surgery. Of the most common invasive monitoring strategies (subdural electrodes [SDEs] and stereo-electroencephalography [sEEG]), the most cost-effective strategy is unknown despite substantial differences in morbidity profiles.

METHODS

Using data collected from an internationally representative sample published in available systematic reviews and meta-analyses, this economic evaluation study employs a decision analysis model to simulate the risks and benefits of SDE and sEEG invasive monitoring strategies. In this model, patients faced differing risks of morbidity, mortality, resection, and seizure freedom depending on which invasive monitoring strategy they underwent. A range of cost values was obtained from a recently published single-center cost-utility analysis. The model considers a base case simulation of a characteristic patient with drug-resistant epilepsy using clinical parameters obtained from systematic reviews of invasive monitoring available in the literature. The main outcome measure was the probability of a positive outcome after invasive monitoring, which was defined as improvement in seizures without a complication. Cost-effectiveness was measured using an incremental cost-effectiveness ratio (ICER).

RESULTS

Invasive monitoring with sEEG had an increased cost of $274 and increased probability of effectiveness of 0.02 compared with SDEs, yielding an ICER of $12,630 per positive outcome obtained. Sensitivity analyses varied parameters widely and revealed consistent model results across the range of clinical parameters reported in the literature. One-way sensitivity analyses revealed that invasive monitoring strategy costs were the most influential parameter for model outcome.

CONCLUSIONS

In this analysis, based on available observational data and estimates of complication costs, invasive monitoring with either SDEs or sEEG was nearly equivalent in terms of cost-effectiveness.

Targeting the Future: Developing a Training Curriculum for Robotic Assisted Neurosurgery

OBJECTIVE

Technological advances have significantly fostered the use of robotics in neurosurgery. Due to their novelty, there is a need to develop training methods within neurosurgical residency programs that provide trainees the skills to utilize these systems in their future practices safely and effectively.

METHODS

We describe a detailed curriculum for trainees with significant responsibilities in the operating room, as well as hands-on and theoretical didactics. The curriculum for robot-assisted stereotactic electroencephalography (SEEG) and deep brain stimulation (DBS) electrode implantation technique and assessment tool has been designed based on Accreditation Council for Graduate Medical Education's (ACGME's) milestone requirement for surgical treatment of epilepsy and movement disorders. Residents were surveyed to assess their use of robotics in their surgical training.

RESULTS

Since 2019, more than 100 patients have undergone robot-assisted SEEG and DBS depth electrode implantations at our institution. Residents and fellows were involved in all aspects of surgical planning and execution and were encouraged to take an active role during procedures. Didactic sessions led by experienced faculty are emphasized as important learning tools prior to hands-on experience in the operating room. The results of the survey show that residents receive more training intraoperatively as compared to training sessions, yet trainees would benefit from more instruction on informative cadaveric simulation sessions.

CONCLUSIONS

Our curriculum was developed to become a structured tool for assessment of robotic education in neurosurgical training. This curriculum based on ACGME milestone requirements serve as a template for resident and fellow education in robotics in neurosurgery.

Thalamic stereoelectroencephalography in epilepsy surgery: a scoping literature review

OBJECTIVE

Stereoelectroencephalography (sEEG) is a well-established surgical method for defining the epileptogenic network. Traditionally reserved for identifying discrete cortical regions for resection or ablation, sEEG in current practice is also used for identifying more broadly involved subcortical epileptic network components, driven by the availability of brain-based neuromodulation strategies. In particular, sEEG investigations including thalamic nuclei are becoming more frequent in parallel with the increase in therapeutic strategies involving thalamic targets such as deep brain stimulation (DBS) and responsive neurostimulation (RNS). The objective to this study was to evaluate existing evidence and trends regarding the purpose, techniques, and relevant electrographic findings of thalamic sEEG.

METHODS

MEDLINE and Embase databases were systematically queried for eligible peer-reviewed studies involving sEEG electrode implantation into thalamic nuclei of patients with epilepsy. Available data were abstracted concerning preoperative workup and purpose for implanting the thalamus, thalamic targets and trajectories, and electrophysiological methodology and findings.

RESULTS

sEEG investigations have included thalamic targets for both basic and clinical research purposes. Medial pulvinar, dorsomedial, anterior, and centromedian nuclei have been the most frequently studied. Few studies have reported any complications with thalamic sEEG implantation, and no studies have reported long-term complications. Various methods have been utilized to characterize thalamic activity in epileptic disorders including evoked potentials, power spectrograms, synchronization indices, and the epileptogenicity index. Thalamic intracranial recordings are beginning to be used to guide neuromodulation strategies including RNS and DBS, as well as to understand complex, network-dependent seizure disorders.

CONCLUSIONS

Inclusion of thalamic coverage during sEEG evaluation in drug-resistant epilepsy is a growing practice and is amenable to various methods of electrographic data analysis. Further study is required to establish well-defined criteria for thalamic implantation during invasive investigations as well as safety and ethical considerations.

Predictive value of magnetoencephalography in guiding the intracranial implant strategy for intractable epilepsy

OBJECTIVE

Magnetoencephalography (MEG) is a useful component of the presurgical evaluation of patients with epilepsy. Due to its high spatiotemporal resolution, MEG often provides additional information to the clinician when forming hypotheses about the epileptogenic zone (EZ). Because of the increasing utilization of stereo-electroencephalography (sEEG), MEG clusters are used to guide sEEG electrode targeting with increasing frequency. However, there are no predefined features of an MEG cluster that predict ictal activity. This study aims to determine which MEG cluster characteristics are predictive of the EZ.

METHODS

The authors retrospectively analyzed all patients who had an MEG study (2017-2021) and underwent subsequent sEEG evaluation. MEG dipoles and sEEG electrodes were reconstructed in the same coordinate space to calculate overlap among individual contacts on electrodes and MEG clusters. MEG cluster features-including number of dipoles, proximity, angle, density, magnitude, confidence parameters, and brain region-were used to predict ictal activity in sEEG. Logistic regression was used to identify important cluster features and to train a binary classifier to predict ictal activity.

RESULTS

Across 40 included patients, 196 electrodes (42.2%) sampled MEG clusters. Electrodes that sampled MEG clusters had higher rates of ictal and interictal activity than those that did not sample MEG clusters (ictal 68.4% vs 39.8%, p < 0.001; interictal 71.9% vs 44.6%, p < 0.001). Logistic regression revealed that the number of dipoles (odds ratio [OR] 1.09, 95% confidence interval [CI] 1.04-1.14, t = 3.43) and confidence volume (OR 0.02, 95% CI 0.00-0.86, t = -2.032) were predictive of ictal activity. This model was predictive of ictal activity with 77.3% accuracy (sensitivity = 80%, specificity = 74%, C-statistic = 0.81). Using only the number of dipoles had a predictive accuracy of 75%, whereas a threshold between 14 and 17 dipoles in a cluster detected ictal activity with 75.9%-85.2% sensitivity.

CONCLUSIONS

MEG clusters with approximately 14 or more dipoles are strong predictors of ictal activity and may be useful in the preoperative planning of sEEG implantation.

Interictal Connectivity Revealed by Granger Analysis of Stereoelectroencephalography: Association With Ictal Onset Zone, Resection, and Outcome

BACKGROUND

Stereoelectroencephalography (sEEG) facilitates electrical sampling and evaluation of complex deep-seated, dispersed, and multifocal locations. Granger causality (GC), previously used to study seizure networks using interictal data from subdural grids, may help identify the seizure-onset zone from interictal sEEG recordings.

OBJECTIVE

To examine whether statistical analysis of interictal sEEG helps identify surgical target sites and whether surgical resection of highly ranked nodes correspond to favorable outcomes.

METHODS

Ten minutes of extraoperative recordings from sequential patients who underwent sEEG evaluation were analyzed (n = 20). GC maps were compared with clinically defined surgical targets using rank order statistics. Outcomes of patients with focal resection/ablation with median follow-up of 3.6 years were classified as favorable (Engel 1, 2) or poor (Engel 3, 4) to assess their relationship with the removal of highly ranked nodes using the Wilcoxon rank-sum test.

RESULTS

In 12 of 20 cases, the rankings of contacts (based on the sum of outward connection weights) mapped to the seizure-onset zone showed higher causal node connectivity than predicted by chance ( P ≤ .02). A very low aggregate probability ( P < 10 -18 , n = 20) suggests that causal node connectivity predicts seizure networks. In 8 of 16 with outcome data, causal connectivity in the resection was significantly greater than in the remaining contacts ( P ≤ .05). We found a significant association between favorable outcome and the presence of highly ranked nodes in the resection ( P < .05).

CONCLUSION

Granger analysis can identify seizure foci from interictal sEEG and correlates highly ranked nodes with favorable outcome, potentially informing surgical decision-making without reliance on ictal recordings.

Subdural electrodes versus stereoelectroencephalography for pediatric epileptogenic zone localization: a retrospective cohort study

OBJECTIVE

The objective of this study was to compare the relative safety and effectiveness of invasive monitoring with subdural electrodes (SDEs) and stereoelectroencephalography (sEEG) in pediatric patients with drug-resistant epilepsy.

METHODS

A retrospective cohort study was performed in 176 patients who underwent invasive monitoring evaluations at UPMC Children’s Hospital of Pittsburgh between January 2000 and September 2021. To examine differences between SDE and sEEG groups, independent-samples t-tests for continuous variables and Pearson chi-square tests for categorical variables were performed. A p value < 0.1 was considered statistically significant.

RESULTS

There were 134 patients (76%) in the SDE group and 42 (24%) in the sEEG group. There was a difference in the proportion with complications (17.9% in the SDE group vs 7.1% in the sEEG group, p = 0.09) and resection (75.4% SDE vs 21.4% sEEG, p < 0.01) between SDE and sEEG patients. However, there was no observable difference in the rates of postresection seizure freedom at 1-year clinical follow-up (60.2% SDE vs 75.0% sEEG, p = 0.55).

CONCLUSIONS

These findings reveal a difference in rates of surgical complications and resection between SDEs and sEEG. Larger prospective, multi-institutional pediatric comparative effectiveness studies may further explore these associations.

Utility of adding electrodes in patients undergoing invasive seizure localization: A case series

Introduction

Surgery can be an effective treatment for epilepsy if the seizure onset is adequately localized. Invasive monitoring is used if noninvasive methods are inconclusive. Initial invasive monitoring may fail if the pre-surgical hypothesis regarding location of epileptic foci is wrong. At this point, a decision must be made whether to remove all electrodes without a clearly defined location of onset or to implant additional electrodes with the aim of achieving localization by expanding coverage.

Methods

Electrodes were placed according to a hypothesis derived from noninvasive monitoring techniques in adult patients with long term epilepsy. Seizure onset was not clearly localized at the end of the invasive monitoring period in ten patients, and additional electrodes were placed based on a new hypothesis that incorporated data from the invasive monitoring period.

Results

Successful localization was achieved in nine patients. There were no complications with adding additional electrodes. At final follow up, four patients were seizure free while four others had at least a 50% reduction in seizures after undergoing surgical intervention.

Conclusion

Seizure foci were localized safely in 90% of adult patients with long term epilepsy after implanting additional electrodes and expanding coverage. Patients undergoing invasive monitoring without clear localization should have additional electrodes placed to expand monitoring coverage as it is safe and effective.

Spontaneous neuronal oscillations in the human insula are hierarchically organized traveling waves

The insula plays a fundamental role in a wide range of adaptive human behaviors, but its electrophysiological dynamics are poorly understood. Here, we used human intracranial electroencephalographic recordings to investigate the electrophysiological properties and hierarchical organization of spontaneous neuronal oscillations within the insula. We analyzed the neuronal oscillations of the insula directly and found that rhythms in the theta and beta frequency oscillations are widespread and spontaneously present. These oscillations are largely organized along the anterior–posterior (AP) axis of the insula. Both the left and right insula showed anterior-­to-posterior decreasing gradients for the power of oscillations in the beta frequency band. The left insula also showed a posterior-to-anterior decreasing frequency gradient and an anterior-to-posterior decreasing power gradient in the theta frequency band. In addition to measuring the power of these oscillations, we also examined the phase of these signals across simultaneous recording channels and found that the insula oscillations in the theta and beta bands are traveling waves. The strength of the traveling waves in each frequency was positively correlated with the amplitude of each oscillation. However, the theta and beta traveling waves were uncoupled to each other in terms of phase and amplitude, which suggested that insular traveling waves in the theta and beta bands operate independently. Our findings provide new insights into the spatiotemporal dynamics and hierarchical organization of neuronal oscillations within the insula, which, given its rich connectivity with widespread cortical regions, indicates that oscillations and traveling waves have an important role in intrainsular and interinsular communications.

Primary Experiences with Robot-assisted Navigation-based Frameless Stereo-electroencephalography: Higher Accuracy than Neuronavigation-guided Manual Adjustment

The use of robot-assisted frameless stereotactic electroencephalography (SEEG) is becoming more common. Among available robotic arms, Stealth Autoguide (SA) (Medtronic, Minneapolis, MN, USA) functions as an optional instrument of the neuronavigation system. The aims of this study were to present our primary experiences with SEEG using SA and to compare the accuracy of implantation between SA and navigation-guided manual adjustment (MA). Seventeen electrodes from two patients who underwent SEEG with SA and 18 electrodes from four patients with MA were retrospectively reviewed. We measured the distance between the planned location and the actual location at entry (De) and the target (Dt) in each electrode. The length of the trajectory did not show a strong correlation with Dt in SA (Pearson's correlation coefficient [r] = 0.099, p = 0.706) or MA (r = 0.233, p = 0.351). De and Dt in SA were shorter than those in MA (1.99 ± 0.90 vs 4.29 ± 1.92 mm, p = 0.0002; 3.59 ± 2.22 vs 5.12 ± 1.40 mm, p = 0.0065, respectively). SA offered higher accuracy than MA both at entry and target. Surgical times per electrode were 38.9 and 32 min in the two patients with SA and ranged from 51.6 to 88.5 min in the four patients with MA. During the implantation period of 10.3 ± 3.6 days, no patients experienced any complications.

Single-center cost comparison analysis of stereoelectroencephalography with subdural grid and strip implantation

OBJECTIVE

Use of invasive stereoelectroencephalography (SEEG) has gained traction recently. However, scant research has investigated the costs and resource utilization of SEEG compared with subdural grid (SDG)-based techniques in pediatric patients. Here, the authors have presented a retrospective analysis of charges associated with SEEG and SDG monitoring at a single institution.

METHODS

The authors performed a retrospective case series analysis of pediatric patients with similar characteristics in terms of age, sex, seizure etiology, and epilepsy treatment strategy who underwent SEEG or SDG monitoring and subsequent craniotomy for resection of epileptogenic focus at St. Louis Children Hospital, St. Louis, Missouri, between 2013 and 2020. Financial data, including hospital charges, supplies, and professional fees (i.e., those related to anesthesia, neurology, neurosurgery, and critical care), were adjusted for inflation to 2020 US dollars.

RESULTS

The authors identified 18 patients (9 underwent SEEG and 9 underwent SDG) with similar characteristics in terms of age (mean [range] 13.6 [1.9-21.8] years for SDG patients vs 11.9 [2.4-19.6] years for SEEG patients, p = 0.607), sex (4 females underwent SDG vs 6 females underwent SEEG, p = 0.637), and presence of lesion (5 patients with a lesion underwent SDG vs 8 underwent SEEG, p = 0.294). All patients underwent subsequent craniotomy for resection of epileptogenic focus. SEEG patients were more likely to have a history of status epilepticus (p = 0.029). Across 1 hospitalization for each SDG patient and 2 hospitalizations for each SEEG patient, SEEG patients had a significantly shorter mean operating room time (288 vs 356 minutes, p = 0.015), mean length of stay in the ICU (1.0 vs 2.1 days, p < 0.001), and tended to have a shorter overall length of stay in the hospital (8.4 vs 10.6 days, p = 0.086). Both groups underwent invasive monitoring for similar lengths of time (5.2 days for SEEG patients vs 6.4 days for SDG patients, p = 0.257). Time to treatment from the initial invasive monitoring evaluation was significantly longer in SEEG patients (64.6 vs 6.4 days, p < 0.001). Neither group underwent readmission within the first 30 days after hospital discharge. Seizure outcomes and complication rates were similar. After adjustment for inflation, the average total perioperative charges were $104,442 for SDG and $106,291 for SEEG (p = 0.800).

CONCLUSIONS

Even though 2 hospitalizations were required for SEEG and 1 hospitalization was required for SDG monitoring, patients who underwent SEEG had a significantly shorter average length of stay in the ICU and operating room time. Surgical morbidity and outcomes were similar. Total perioperative charges for invasive monitoring and resection were approximately 2% higher for SEEG patients when corrected for inflation, but this difference was not statistically significant.

Theoretical stereoelectroencephalography density on the brain convexity

INTRODUCTION

Invasive electroencephalography (EEG) remains the "gold standard" for diagnosing the epileptogenic zone in patients with drug-resistant epilepsy and discrepancies between seizure semiology, video-EEG and magnetic resonance imaging (MRI) findings. However, the possibilities of stereoelectroencephalography (SEEG) to explore the brain surface remain a matter of debate and subdural EEG (SDEEG) is still preferred in some centers for cases when the supposed epileptogenic zone is on the brain convexity. The aim of our study was to evaluate the theoretical safe SEEG coverage on the brain convexity and to compare the theoretical SEEG cortical density with the usual SDEEG density.

MATERIALS AND METHODS

Our material included 10 hemispheres in 5 patients, who had been already investigated with SEEG for drug-resistant epilepsy. We translated our previously described technique in a theoretical model in an attempt to calculate the maximal number of avascular windows for each cerebral hemisphere. The distance between every entry point and the other entry points for each hemisphere was calculated using a mathematical formula. Subsequently, the theoretical SEEG coverage on the brain convexity was described using the maximal, minimal and average distances between each entry point and the closest 4 neighboring points. This type of measurement allows a direct comparison between SEEG and SDEEG in their ability to explore the brain convexity.

RESULTS

Ten hemispheres had 1328 safe entry points with a safety margin of 2.5 mm and a minimal distance of 2.5 mm between 2 entry points (average number of entry points: 132.8 (SD ± 5). The number of entry points in the explored 10 hemispheres varied from 104 to 156. The average distance between each entry point and its 4 neighbors was 11.47 mm. The maximal distance between two entry points in these 10 hemispheres was ranging from 20.28 to 27.23 mm (average: 24.67 mm). The closest entry points for the explored hemispheres were at an average distance of 4.67 mm (range: 2.82 - 5.96 mm). The average convexity surface was 223.68 cm2 (range: 204.63-238.77 cm2). The safe electrode density without electrode collision on the cortical surface was ranging from 0.46 to 0.69 electrodes per cm2 (average: 0.59 electrodes per cm2) (SD ± 0.023).

CONCLUSION

The theoretical SEEG cortical density is comparable with the usual SDEEG density. These findings, combined with the better safety profile of SEEG and the possibilities to explore deep cortical structures, explain the progressive shift from SDEEG to SEEG during the last years.

LeGUI: A Fast and Accurate Graphical User Interface for Automated Detection and Anatomical Localization of Intracranial Electrodes

Accurate anatomical localization of intracranial electrodes is important for identifying the seizure foci in patients with epilepsy and for interpreting effects from cognitive studies employing intracranial electroencephalography. Localization is typically performed by coregistering postimplant computed tomography (CT) with preoperative magnetic resonance imaging (MRI). Electrodes are then detected in the CT, and the corresponding brain region is identified using the MRI. Many existing software packages for electrode localization chain together separate preexisting programs or rely on command line instructions to perform the various localization steps, making them difficult to install and operate for a typical user. Further, many packages provide solutions for some, but not all, of the steps needed for confident localization. We have developed software, Locate electrodes Graphical User Interface (LeGUI), that consists of a single interface to perform all steps needed to localize both surface and depth/penetrating intracranial electrodes, including coregistration of the CT to MRI, normalization of the MRI to the Montreal Neurological Institute template, automated electrode detection for multiple types of electrodes, electrode spacing correction and projection to the brain surface, electrode labeling, and anatomical targeting. The software is written in MATLAB, core image processing is performed using the Statistical Parametric Mapping toolbox, and standalone executable binaries are available for Windows, Mac, and Linux platforms. LeGUI was tested and validated on 51 datasets from two universities. The total user and computational time required to process a single dataset was approximately 1 h. Automatic electrode detection correctly identified 4362 of 4695 surface and depth electrodes with only 71 false positives. Anatomical targeting was verified by comparing electrode locations from LeGUI to locations that were assigned by an experienced neuroanatomist. LeGUI showed a 94% match with the 482 neuroanatomist-assigned locations. LeGUI combines all the features needed for fast and accurate anatomical localization of intracranial electrodes into a single interface, making it a valuable tool for intracranial electrophysiology research.

Speech-related auditory salience detection in the posterior superior temporal region

Processing auditory human speech requires both detection (early and transient) and analysis (sustained). We analyzed high gamma (70-110 Hz) activity of intracranial electroencephalography waveforms acquired during an auditory task that paired forward speech, reverse speech, and signal correlated noise. We identified widespread superior temporal sites with sustained activity responding only to forward and reverse speech regardless of paired order. More localized superior temporal auditory onset sites responded to all stimulus types when presented first in a pair and responded in recurrent fashion to the second paired stimulus in select conditions even in the absence of interstimulus silence; a novel finding. Auditory onset activity to a second paired sound recurred according to relative salience, with evidence of partial suppression during linguistic processing. We propose that temporal lobe auditory onset sites facilitate a salience detector function with hysteresis of 200 ms and are influenced by cortico-cortical feedback loops involving linguistic processing and articulation.

Probabilistic comparison of gray and white matter coverage between depth and surface intracranial electrodes in epilepsy

In this study, we quantified the coverage of gray and white matter during intracranial electroencephalography in a cohort of epilepsy patients with surface and depth electrodes. We included 65 patients with strip electrodes (n = 12), strip and grid electrodes (n = 24), strip, grid, and depth electrodes (n = 7), or depth electrodes only (n = 22). Patient-specific imaging was used to generate probabilistic gray and white matter maps and atlas segmentations. Gray and white matter coverage was quantified using spherical volumes centered on electrode centroids, with radii ranging from 1 to 15 mm, along with detailed finite element models of local electric fields. Gray matter coverage was highly dependent on the chosen radius of influence (RoI). Using a 2.5 mm RoI, depth electrodes covered more gray matter than surface electrodes; however, surface electrodes covered more gray matter at RoI larger than 4 mm. White matter coverage and amygdala and hippocampal coverage was greatest for depth electrodes at all RoIs. This study provides the first probabilistic analysis to quantify coverage for different intracranial recording configurations. Depth electrodes offer increased coverage of gray matter over other recording strategies if the desired signals are local, while subdural grids and strips sample more gray matter if the desired signals are diffuse.

Development and Validation of the 5-SENSE Score to Predict Focality of the Seizure-Onset Zone as Assessed by Stereoelectroencephalography

Importance

Stereoelectroencephalography (SEEG) has become the criterion standard in case of inconclusive noninvasive presurgical epilepsy workup. However, up to 40% of patients are subsequently not offered surgery because the seizure-onset zone is less focal than expected or cannot be identified.

Objective

To predict focality of the seizure-onset zone in SEEG, the 5-point 5-SENSE score was developed and validated.

Design, Setting, and Participants

This was a monocentric cohort study for score development followed by multicenter validation with patient selection intervals between February 2002 to October 2018 and May 2002 to December 2019. The minimum follow-up period was 1 year. Patients with drug-resistant epilepsy undergoing SEEG at the Montreal Neurological Institute were analyzed to identify a focal seizure-onset zone. Selection criteria were 2 or more seizures in electroencephalography and availability of complete neuropsychological and neuroimaging data sets. For validation, patients from 9 epilepsy centers meeting these criteria were included. Analysis took place between May and July 2021.

Main Outcomes and Measures

Based on SEEG, patients were grouped as focal and nonfocal seizure-onset zone. Demographic, clinical, electroencephalography, neuroimaging, and neuropsychology data were analyzed, and a multiple logistic regression model for developing a score to predict SEEG focality was created and validated in an independent sample.

Results

A total of 128 patients (57 women [44.5%]; median [range] age, 31 [13-58] years) were analyzed for score development and 207 patients (97 women [46.9%]; median [range] age, 32 [16-70] years) were analyzed for validation. The score comprised the following 5 predictive variables: focal lesion on structural magnetic resonance imaging, absence of bilateral independent spikes in scalp electroencephalography, localizing neuropsychological deficit, strongly localizing semiology, and regional ictal scalp electroencephalography onset. The 5-SENSE score had an optimal mean (SD) probability cutoff for identifying a focal seizure-onset zone of 37.6 (3.5). Area under the curve, specificity, and sensitivity were 0.83, 76.3% (95% CI, 66.7-85.8), and 83.3% (95% CI, 72.30-94.1), respectively. Validation showed 76.0% (95% CI, 67.5-84.0) specificity and 52.3% (95% CI, 43.0-61.5) sensitivity.

Conclusions and Relevance

High specificity in score development and validation confirms that the 5-SENSE score predicts patients where SEEG is unlikely to identify a focal seizure-onset zone. It is a simple and useful tool for assisting clinicians to reduce unnecessary invasive diagnostic burden on patients and overutilization of limited health care resources.

Comparative Effectiveness of Stereotactic Electroencephalography Versus Subdural Grids in Epilepsy Surgery

OBJECTIVE

The aim was to compare the outcomes of subdural electrode (SDE) implantations versus stereotactic electroencephalography (SEEG), the 2 predominant methods of intracranial electroencephalography (iEEG) performed in difficult-to-localize drug-resistant focal epilepsy.

METHODS

The Surgical Therapies Commission of the International League Against Epilepsy created an international registry of iEEG patients implanted between 2005 and 2019 with ≥1 year of follow-up. We used propensity score matching to control exposure selection bias and generate comparable cohorts. Study endpoints were: (1) likelihood of resection after iEEG; (2) seizure freedom at last follow-up; and (3) complications (composite of postoperative infection, symptomatic intracranial hemorrhage, or permanent neurological deficit).

RESULTS

Ten study sites from 7 countries and 3 continents contributed 2,012 patients, including 1,468 (73%) eligible for analysis (526 SDE and 942 SEEG), of whom 988 (67%) underwent subsequent resection. Propensity score matching improved covariate balance between exposure groups for all analyses. Propensity-matched patients who underwent SDE had higher odds of subsequent resective surgery (odds ratio [OR] = 1.4, 95% confidence interval [CI] 1.05, 1.84) and higher odds of complications (OR = 2.24, 95% CI 1.34, 3.74; unadjusted: 9.6% after SDE vs 3.3% after SEEG). Odds of seizure freedom in propensity-matched resected patients were 1.66 times higher (95% CI 1.21, 2.26) for SEEG compared with SDE (unadjusted: 55% seizure free after SEEG-guided resections vs 41% after SDE).

INTERPRETATION

In comparison to SEEG, SDE evaluations are more likely to lead to brain surgery in patients with drug-resistant epilepsy but have more surgical complications and lower probability of seizure freedom. This comparative-effectiveness study provides the highest feasible evidence level to guide decisions on iEEG. ANN NEUROL 2021.

Robotic-assisted stereotactic drainage of cerebral abscess and placement of ventriculostomy

BACKGROUND

Robotic surgery has found increasing use in multiple subfields of neurosurgery. While the initial applications of stereotactic robotic surgery were for the placement of electrodes for extra-operative seizure monitoring, this technique has become increasingly relevant in other areas of neurosurgery. To the best of our knowledge, we report the first case of successful robotic surgery utilization to drain a cerebral abscess and place an external ventricular drain.

CASE REPORT

The authors demonstrate a novel use for stereotactic robotic assistance to drain a cerebral abscess and place ventriculostomy in a 74-year-old female patient who presented with a left basal ganglia Streptococcus intermedius abscess and concomitant ventriculitis. Drainage of a deep-seated abscess and placement of ventriculostomy was successfully performed in this patient without intraoperative difficulties or complications. The total operative time, including registration was 64 minutes and the estimated blood loss was 25 mL. The patient recovered well and was discharged to inpatient rehabilitation on postoperative day 19.

CONCLUSIONS

The use of robotic surgery to drain cerebral abscesses and place ventriculostomies is technically feasible and may potentially decrease operative time and increase accuracy and safety.

Comparison of robotic and manual implantation of intracerebral electrodes: a single-centre, single-blinded, randomised controlled trial

There has been a significant rise in robotic trajectory guidance devices that have been utilised for stereotactic neurosurgical procedures. These devices have significant costs and associated learning curves. Previous studies reporting devices usage have not undertaken prospective parallel-group comparisons before their introduction, so the comparative differences are unknown. We study the difference in stereoelectroencephalography electrode implantation time between a robotic trajectory guidance device (iSYS1) and manual frameless implantation (PAD) in patients with drug-refractory focal epilepsy through a single-blinded randomised control parallel-group investigation of SEEG electrode implantation, concordant with CONSORT statement. Thirty-two patients (18 male) completed the trial. The iSYS1 returned significantly shorter median operative time for intracranial bolt insertion, 6.36 min (95% CI 5.72–7.07) versus 9.06 min (95% CI 8.16–10.06), p = 0.0001. The PAD group had a better median target point accuracy 1.58 mm (95% CI 1.38–1.82) versus 1.16 mm (95% CI 1.01–1.33), p = 0.004. The mean electrode implantation angle error was 2.13° for the iSYS1 group and 1.71° for the PAD groups (p = 0.023). There was no statistically significant difference for any other outcome. Health policy and hospital commissioners should consider these differences in the context of the opportunity cost of introducing robotic devices.

Trial registration: ISRCTN17209025 (https://doi.org/10.1186/ISRCTN17209025).

sEEG for Expansion of a Surgical Epilepsy Program: Safety and Efficacy in 152 Consecutive Cases

Objective

Stereoelectroencephalography (sEEG) is an intracranial encephalography method of expanding use. The need for increased epilepsy surgery access has led to the consideration of sEEG adoption by new or expanding surgical epilepsy programs. Data regarding safety and efficacy are uncommon outside of high‐volume, well‐established centers, which may be less applicable to newer or low‐volume centers. The objective of this study was to add to the sEEG outcomes in the literature from the perspective of a rapidly expanding center.

Methods

A retrospective chart review of consecutive sEEG cases from January 2016 to December 2019 was performed. Data extraction included demographic data, surgical data, and outcome data, which pertinently examined surgical method, progression to therapeutic procedure, clinically significant adverse events, and Engel outcomes.

Results

One hundred and fifty‐two sEEG procedures were performed on 131 patients. Procedures averaged 10.5 electrodes for a total of 1603 electrodes. The majority (84%) of patients progressed to a therapeutic procedure. Six clinically significant complications occurred: three retained electrodes, two hemorrhages, and one failure to complete investigation. Only one complication resulted in a permanent deficit. Engel 1 outcome was achieved in 63.3% of patients reaching one‐year follow‐up after a curative procedure.

Significance

New or expanding epilepsy surgery centers can appropriately consider the use of sEEG. The complication rate is low and the majority of patients progress to therapeutic surgery. Procedural safety, progression to therapeutic intervention, and Engel outcomes are comparable to cohorts from long‐established epilepsy surgery programs.

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

Background:

Paralysis and neuropathy, affecting millions of people worldwide, can be accompanied by significant loss of somatosensation. With tactile sensation being central to achieving dexterous movement, brain-computer interface (BCI) researchers have used intracortical and cortical surface electrical stimulation to restore somatotopically-relevant sensation to the hand. However, these approaches are restricted to stimulating the gyral areas of the brain. Since representation of distal regions of the hand extends into the sulcal regions of human primary somatosensory cortex (S1), it has been challenging to evoke sensory percepts localized to the fingertips.

Objective/hypothesis:

Targeted stimulation of sulcal regions of S1, using stereoelectroencephalography (SEEG) depth electrodes, can evoke focal sensory percepts in the fingertips.

Methods:

Two participants with intractable epilepsy received cortical stimulation both at the gyri via high-density electrocorticography (HD-ECoG) grids and in the sulci via SEEG depth electrode leads. We characterized the evoked sensory percepts localized to the hand.

Results:

We show that highly focal percepts can be evoked in the fingertips of the hand through sulcal stimulation. fMRI, myelin content, and cortical thickness maps from the Human Connectome Project elucidated specific cortical areas and sub-regions within S1 that evoked these focal percepts. Within-participant comparisons showed that percepts evoked by sulcal stimulation via SEEG electrodes were significantly more focal (80% less area; p = 0.02) and localized to the fingertips more often, than by gyral stimulation via HD-ECoG electrodes. Finally, sulcal locations with consistent modulation of high-frequency neural activity during mechanical tactile stimulation of the fingertips showed the same somatotopic correspondence as cortical stimulation.

Conclusions:

Our findings indicate minimally invasive sulcal stimulation via SEEG electrodes could be a clinically viable approach to restoring sensation.

Stereotactic Electroencephalography Implantation Through Nonautologous Cranioplasty: Proof of Concept

BACKGROUND

Stereoelectroencephalography (SEEG) is an effective method to define the epileptogenic zone (EZ) in patients with medically intractable epilepsy. Typical placement requires passing and anchoring electrodes through native skull.

OBJECTIVE

To describe the successful placement of SEEG electrodes in patients without native bone. To the best of our knowledge, the use of SEEG in patients with nonautologous cranioplasties has not been described.

METHODS

We describe 3 cases in which SEEG was performed through nonautologous cranioplasty. The first is a 30-yr-old male with a titanium mesh cranioplasty following a left pterional craniotomy for aneurysm clipping. The second is a 51-yr-old female who previously underwent lesionectomy of a ganglioglioma with mesh cranioplasty and subsequent recurrence of her seizures. The third is a 31-yr-old male with a polyether ether ketone cranioplasty following decompressive hemicraniectomy for trauma.

RESULTS

SEEG was performed successfully in all three cases without intraoperative difficulties or complications and with excellent electroencephalogram recording and optimal localization of the seizure focus. The EZ was successfully localized in all three patients. There were no limitations related to drilling or inserting the guiding bolt/electrode through the nonautologous cranioplasties.

CONCLUSION

SEEG through nonautologous cranioplasties was clinically feasible, safe, and effective in our series. The presence of nonautologous bone cranioplasty should not preclude such patients from undergoing SEEG explorations.

Stereotactic Electroencephalography Is Associated With Reduced Pain and Opioid Use When Compared with Subdural Grids: A Case Series

BACKGROUND

Minimally invasive surgery (MIS) has been shown to decrease length of hospital stay and opioid use.

OBJECTIVE

To identify whether surgery for epilepsy mapping via MIS stereotactically placed electroencephalography (SEEG) electrodes decreased overall opioid use when compared with craniotomy for EEG grid placement (ECoG).

METHODS

Patients who underwent surgery for epilepsy mapping, either SEEG or ECoG, were identified through retrospective chart review from 2015 through 2018. The hospital stay was separated into specific time periods to distinguish opioid use immediately postoperatively, throughout the rest of the stay and at discharge. The total amount of opioids consumed during each period was calculated by transforming all types of opioids into their morphine equivalents (ME). Pain scores were also collected using a modification of the Clinically Aligned Pain Assessment (CAPA) scale. The 2 surgical groups were compared using appropriate statistical tests.

RESULTS

The study identified 43 patients who met the inclusion criteria: 36 underwent SEEG placement and 17 underwent craniotomy grid placement. There was a statistically significant difference in median opioid consumption per hospital stay between the ECoG and the SEEG placement groups, 307.8 vs 71.5 ME, respectively (P = .0011). There was also a significant difference in CAPA scales between the 2 groups (P = .0117).

CONCLUSION

Opioid use is significantly lower in patients who undergo MIS epilepsy mapping via SEEG compared with those who undergo the more invasive ECoG procedure. As part of efforts to decrease the overall opioid burden, these results should be considered by patients and surgeons when deciding on surgical methods.

Difficult-to-Localize Epilepsy After Stereoelectroencephalography: Technique, Safety, and Efficacy of Placing Additional Electrodes During the Same Admission

BACKGROUND

Stereoelectroencephalography (SEEG) is used to identify the epileptogenic zone (EZ) in patients with epilepsy for potential surgical intervention. Occasionally, the EZ is difficult to localize even after an SEEG implantation.

OBJECTIVE

To demonstrate a safe technique for placing additional electrodes in ongoing SEEG evaluations. Describe efficacy, complications, and surgical outcomes.

METHODS

An operative technique which involves maintaining previously placed electrodes and sterilely placing new electrodes was developed and implemented. All patients who underwent placement of additional SEEG electrodes during the same admission were retrospectively reviewed.

RESULTS

A total of 14 patients met criteria and had undergone SEEG evaluation with 198 electrodes implanted. A total 93% of patients (13/14) had nonlesional epilepsy. After unsuccessful localization of the EZ after a mean of 9.6 d of monitoring, each patient underwent additional placement of electrodes (5.5 average electrodes per patient) to augment the original implantation. At no point did any patients develop new hemorrhage, infection, wound breakdown, or require any kind of additional antimicrobial treatment. A total 64% (9/14) of patients were able to undergo surgery aimed at removing the EZ guided by the additional SEEG electrodes. A total 44% (4/9) of surgical patients had Engel class I outcomes at an average follow-up time of 11 mo.

CONCLUSION

Placing additional SEEG electrodes, while maintaining the previously placed electrodes, appears to be safe, effective, and had no infectious complications. When confronted with difficult-to-localize epilepsy even after invasive monitoring, it appears to be safe and potentially clinically effective to place additional electrodes during the same admission.

VarioGuide® frameless neuronavigation-guided stereoelectroencephalography in adult epilepsy patients: technique, accuracy and clinical experience

Background

Stereoelectroencephalography (SEEG) allows the identification of deep-seated seizure foci and determination of the epileptogenic zone (EZ) in drug-resistant epilepsy (DRE) patients. We evaluated the accuracy and treatment-associated morbidity of frameless VarioGuide® (VG) neuronavigation-guided depth electrode (DE) implantations.

Methods

We retrospectively identified all consecutive adult DRE patients, who underwent VG-neuronavigation DE implantations, between March 2013 and April 2019. Clinical data were extracted from the electronic patient charts. An interdisciplinary team agreed upon all treatment decisions. We performed trajectory planning with iPlan® Cranial software and DE implantations with the VG system. Each electrode’s accuracy was assessed at the entry (EP), the centre (CP) and the target point (TP). We conducted correlation analyses to identify factors associated with accuracy.

Results

The study population comprised 17 patients (10 women) with a median age of 32.0 years (range 21.0–54.0). In total, 220 DEs (median length 49.3 mm, range 25.1–93.8) were implanted in 21 SEEG procedures (range 3–16 DEs/surgery). Adequate signals for postoperative SEEG were detected for all but one implanted DEs (99.5%); in 15/17 (88.2%) patients, the EZ was identified and 8/17 (47.1%) eventually underwent focus resection. The mean deviations were 3.2 ± 2.4 mm for EP, 3.0 ± 2.2 mm for CP and 2.7 ± 2.0 mm for TP. One patient suffered from postoperative SEEG-associated morbidity (i.e. conservatively treated delayed bacterial meningitis). No mortality or new neurological deficits were recorded.

Conclusions

The accuracy of VG-SEEG proved sufficient to identify EZ in DRE patients and associated with a good risk-profile. It is a viable and safe alternative to frame-based or robotic systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-021-04755-w.

Gray Matter Sampling Differences Between Subdural Electrodes and Stereoelectroencephalography Electrodes

Objective: Stereoelectroencephalography (SEEG) has seen a recent increase in popularity in North America; however, concerns regarding the spatial sampling capabilities of SEEG remain. We aimed to quantify and compare the spatial sampling of subdural electrode (SDE) and SEEG implants.

Methods: Patients with drug-resistant epilepsy who underwent invasive monitoring were included in this retrospective case-control study. Ten SEEG cases were compared with ten matched SDE cases based on clinical presentation and pre-implantation hypothesis. To quantify gray matter sampling, MR and CT images were coregistered and a 2.5mm radius sphere was superimposed over the center of each electrode contact. The estimated recording volume of gray matter was defined as the cortical voxels within these spherical models. Paired t-tests were performed to compare volumes and locations of SDE and SEEG recording. A Ripley's K-function analysis was performed to quantify differences in spatial distributions.

Results: The average recording volume of gray matter by each individual contact was similar between the two modalities. SEEG implants sampled an average of 20% more total gray matter, consisted of an average of 17% more electrode contacts, and had 77% more of their contacts covering gray matter within sulci. Insular coverage was only achieved with SEEG. SEEG implants generally consist of discrete areas of dense local coverage scattered across the brain; while SDE implants cover relatively contiguous areas with lower density recording.

Significance: Average recording volumes per electrode contact are similar for SEEG and SDE, but SEEG may allow for greater overall volumes of recording as more electrodes can be routinely implanted. The primary difference lies in the location and distribution of gray matter than can be sampled. The selection between SEEG and SDE implantation depends on sampling needs of the invasive implant.

Fast Automated Stereo-EEG Electrode Contact Identification and Labeling Ensemble

INTRODUCTION

Stereotactic electroencephalography (SEEG) has emerged as the preferred modality for intracranial monitoring in drug-resistant epilepsy (DRE) patients being evaluated for neurosurgery. After implantation of SEEG electrodes, it is important to determine the neuroanatomic locations of electrode contacts (ECs), to localize ictal onset and propagation, and integrate functional information to facilitate surgical decisions. Although there are tools for coregistration of preoperative MRI and postoperative CT scans, identification, sorting, and labeling of SEEG ECs is often performed manually, which is resource intensive. We report development and validation of a software named Fast Automated SEEG Electrode Contact Identification and Labeling Ensemble (FASCILE).

METHODS

FASCILE is written in Python 3.8.3 and employs a novel automated method for identifying ECs, assigning them to respected SEEG electrodes, and labeling. We compared FASCILE with our clinical process of identifying, sorting, and labeling ECs, by computing localization error in anteroposterior, superoinferior, and lateral dimensions. We also measured mean Euclidean distances between ECs identified by FASCILE and the clinical method. We compared time taken for EC identification, sorting, and labeling for the software developer using FASCILE, a first-time clinical user using FASCILE, and the conventional clinical process.

RESULTS

Validation in 35 consecutive DRE patients showed a mean overall localization error of 0.73 ± 0.15 mm. FASCILE required 10.7 ± 5.5 min/patient for identifying, sorting, and labeling ECs by a first-time clinical user, compared to 3.3 ± 0.7 h/patient required for the conventional clinical process.

CONCLUSION

Given the accuracy, speed, and ease of use, we expect FASCILE to be used frequently for SEEG-driven epilepsy surgery. It is freely available for noncommercial use. FASCILE is specifically designed to expedite localization of ECs, assigning them to respective SEEG electrodes (sorting), and labeling them and not for coregistration of CT and MRI data as there are commercial software available for this purpose.

Efficient automated localization of ECoG electrodes in CT images via shape analysis

Purpose

People with drug-refractory epilepsy are potential candidates for surgery. In many cases, epileptogenic zone localization requires intracranial investigations, e.g., via ElectroCorticoGraphy (ECoG), which uses subdural electrodes to map eloquent areas of large cortical regions. Precise electrodes localization on cortical surface is mandatory to delineate the seizure onset zone. Simple thresholding operations performed on patients’ computed tomography (CT) volumes recognize electrodes but also other metal objects (e.g., wires, stitches), which need to be manually removed. A new automated method based on shape analysis is proposed, which provides substantially improved performances in ECoG electrodes recognition.

Methods

The proposed method was retrospectively tested on 24 CT volumes of subjects with drug-refractory focal epilepsy, presenting a large number (> 1700) of round platinum electrodes. After CT volume thresholding, six geometric features of voxel clusters (volume, symmetry axes lengths, circularity and cylinder similarity) were used to recognize the actual electrodes among all metal objects via a Gaussian support vector machine (G-SVM). The proposed method was further tested on seven CT volumes from a public repository. Simultaneous recognition of depth and ECoG electrodes was also investigated on three additional CT volumes, containing penetrating depth electrodes.

Results

The G-SVM provided a 99.74% mean classification accuracy across all 24 single-patient datasets, as well as on the combined dataset. High accuracies were obtained also on the CT volumes from public repository (98.27% across all patients, 99.68% on combined dataset). An overall accuracy of 99.34% was achieved for the recognition of depth and ECoG electrodes.

Conclusions

The proposed method accomplishes automated ECoG electrodes localization with unprecedented accuracy and can be easily implemented into existing software for preoperative analysis process. The preliminary yet surprisingly good results achieved for the simultaneous depth and ECoG electrodes recognition are encouraging.

Ethical approval n°NCT04479410 by “IRCCS Neuromed” (Pozzilli, Italy), 30th July 2020.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11548-021-02325-0.

Accuracy and Feasibility Analysis of SEEG Electrode Implantation using the VarioGuide Frameless Navigation System in Patients with Drug-Resistant Epilepsy

OBJECTIVE

 The objective of the study was to evaluate the feasibility and accuracy of frameless stereoelectroencephalography (SEEG) electrode implantation in patients with drug-resistant epilepsy using the VarioGuide system.

METHODS

 The VarioGuide frameless navigation system was used to implant SEEG electrodes in patients with medically drug-resistant epilepsy. Demographic data, surgery duration, number of electrodes, and complications were retrospectively analyzed. Accuracy was compared by measuring the distance between the planned and actual electrode positions as determined by postoperative computed tomography images.

RESULTS

 A total of 141 SEEG electrodes were implanted in 19 patients from May 2015 to December 2018 with an average of 7.42 (range: 4-10) leads per patient. The average entry point localization error (EPLE) was 1.96 ± 0.47 mm (range: 0.32-3.29) and average target point localization error (TPLE) was 2.47 ± 0.79 mm (range: 0.72-4.83). The average operating time per lead (OTPL) was 14.16 ± 2.68 minutes (range: 8.64-21.58). No complications occurred.

CONCLUSION

 The VarioGuide frameless navigation system can be an effective method for SEEG electrode implantation in patients with drug-resistant epilepsy, particularly when the electrodes are concentrated in a relatively small region and the number of implanted electrodes is small.

Cost-effectiveness analysis of invasive EEG monitoring in drug-resistant epilepsy

PURPOSE

Our aim was to determine the cost-effectiveness of two intracranial electroencephalography (iEEG) interventions: 1) stereoelectroencephalography (SEEG) and 2) placement of subdural grid electrodes (SDGs) both followed by resective surgery in patients with drug-resistant, partial-onset epilepsy, compared with medical management (MM) in Hungary from payer's perspective.

METHODS

The incremental health gains and costs of iEEG interventions have been determined with a combination of a decision tree and prevalence Markov process model over a 30-year time horizon in a cost-utility analysis (CUA). To address the effect of parameter uncertainty on the incremental cost-effectiveness ratio (ICER), deterministic and probabilistic sensitivity analyses were performed.

RESULTS

Our results showed that both SEEG and SDG interventions represent a more expensive but more effective strategy than MM representing the current standard of care. The total discounted cost of SEEG and SDG were € 32,760 and € 25,028 representing € 18,108 and € 10,375 additional cost compared with MM, respectively. However, they provide an additional 3.931 (in SEEG group) and 3.444 quality-adjusted life years (QALYs; in SDG group), correspondingly. Thus, the ICER of SEEG is € 4607 per QALY gain, while the ICER for SDG is € 3013 per QALY gain, compared with MM. At a cost-effectiveness threshold of € 41,058 per QALY in Hungary, both subtypes of iEEG interventions are cost-effective and provide good value for money.

SIGNIFICANCE

Because of the high cost of implanting electrodes and monitoring, the invasive EEG for patients with refractory epilepsy is currently not available in the Hungarian national healthcare system. Our study demonstrated that these procedures in Hungary are cost-effective compared with the MM. As a result, the introduction of iEEG interventions to the reimbursement list of the National Health Insurance Fund Administration was initiated.

Contributions of Robotics to the Safety and Efficacy of Invasive Monitoring With Stereoelectroencephalography

The purpose of this review is to provide a discussion of the history and utility of robotics in invasive monitoring for epilepsy surgery using stereoelectroencephalography (sEEG). The authors conducted a literature review of available sources to describe how the advent of surgical robotics has improved the efficacy and ease of performing sEEG surgery. The sEEG method integrates anatomic, electrographic, and clinical information to test hypotheses regarding the localization of the epileptogenic zone (EZ) and has been used in Europe since the 1950s. One of the primary benefits of robot-assisted sEEG implantation techniques is the ability to seamlessly transition between both orthogonal and oblique trajectory types using a single technique. Based on available information, it is our view that, when applied appropriately, robotic sEEG can have a low rate of complications and many advantages over both non-robotic sEEG implantation and traditional craniotomy-based invasive monitoring methods.