Surgical outcomes related to invasive EEG monitoring with subdural grids or depth electrodes in adults: A systematic review and meta-analysis

Functional Brain Mapping Using Depth Electrodes

OBJECTIVE

This study investigated the neurologic symptoms and stimulus intensities in the stimulation of deep structures and subcortical fibers with the depth electrodes.

METHODS

Seventeen patients with drug-refractory epilepsy who underwent functional brain mapping with the depth electrodes were enrolled. The 50 Hz electrical stimulation was applied, and the diffusion tensor image was used to identify subcortical fibers. The responsible structures and stimulus intensities for the induced neurologic symptoms were evaluated.

RESULTS

Neurologic symptoms were induced in 11 of 17 patients. The opercular stimulation elicited the neurologic symptoms in 6 patients at the median threshold of 4.0 mA (visceral/face/hand sensory, hand/throat motor, negative motor and auditory symptoms). The insular stimulation induced the neurologic symptoms in 4 patients at the median threshold of 4.0 mA (auditory, negative motor, and sensory symptoms). The stimulation of subcortical fibers was induced in 5 of 9 patients at the median threshold of 4.5 mA. The thresholds of depth electrodes were significantly lower than those of subdural electrodes in 8 patients who used both subdural and depth electrodes and induced symptoms with both electrodes.

CONCLUSIONS

The stimulation of depth electrodes can identify the function of deep structures and subcortical fibers with lower intensities than subdural electrodes.

Non-lesional epilepsy does not necessarily convey poor outcomes after invasive monitoring followed by resection or thermal ablation

OBJECTIVE

We aimed to compare outcomes including seizure-free status at the last follow-up in adult patients with medically refractory focal epilepsy identified as lesional vs. non-lesional based on their magnetic resonance imaging (MRI) findings who underwent invasive evaluation followed by subsequent resection or thermal ablation (LiTT).

METHODS

We identified 88 adult patients who underwent intracranial monitoring between 2014 and 2021. Of those, 40 received resection or LiTT, and they were dichotomized based on MRI findings, as lesional (N = 28) and non-lesional (N = 12). Patient demographics, seizure characteristics, non-invasive interventions, intracranial monitoring, and surgical variables were compared between the groups. Postsurgical seizure outcome at the last follow-up was rated according to the Engel classification, and postoperative seizure freedom was determined by Kaplan-Meyer survival analysis. Statistical analyses employed Fisher's exact test to compare categorical variables, while a t-test was used for continuous variables.

RESULTS

There were no differences in baseline characteristics between groups except for more often noted PET abnormality in the lesional group (p = 0.0003). 64% of the lesional group and 57% of the non-lesional group received surgical resection or LiTT (p = 0.78). At the last follow-up, 78.5% of the patients with lesional MRI findings achieved Engel I outcomes compared to 66.7% of non-lesional patients (p = 0.45). Kaplan-Meier curves did not show a significant difference in seizure-free duration between both groups after surgical intervention (p = 0.49).

SIGNIFICANCE

In our sample, the absence of lesion on brain MRI was not associated with worse seizure outcomes in adult patients who underwent invasive intracranial monitoring followed by resection or thermal ablation.

Depth versus surface: A critical review of subdural and depth electrodes in intracranial electroencephalographic studies

Intracranial electroencephalographic (IEEG) recording, using subdural electrodes (SDEs) and stereoelectroencephalography (SEEG), plays a pivotal role in localizing the epileptogenic zone (EZ). SDEs, employed for superficial cortical seizure foci localization, provide information on two-dimensional seizure onset and propagation. In contrast, SEEG, with its three-dimensional sampling, allows exploration of deep brain structures, sulcal folds, and bihemispheric networks. SEEG offers the advantages of fewer complications, better tolerability, and coverage of sulci. Although both modalities allow electrical stimulation, SDE mapping can tessellate cortical gyri, providing the opportunity for a tailored resection. With SEEG, both superficial gyri and deep sulci can be stimulated, and there is a lower risk of afterdischarges and stimulation-induced seizures. Most systematic reviews and meta-analyses have addressed the comparative effectiveness of SDEs and SEEG in localizing the EZ and achieving seizure freedom, although discrepancies persist in the literature. The combination of SDEs and SEEG could potentially overcome the limitations inherent to each technique individually, better delineating seizure foci. This review describes the strengths and limitations of SDE and SEEG recordings, highlighting their unique indications in seizure localization, as evidenced by recent publications. Addressing controversies in the perceived usefulness of the two techniques offers insights that can aid in selecting the most suitable IEEG in clinical practice.

Predictors of SOZ localization, subsequent surgical intervention, and seizure outcomes in iEEG

OBJECTIVE

A third of the patients who undergo intracranial EEG (iEEG) for seizure-onset zone (SOZ) localization do not proceed to resective surgery for epilepsy, and over half of those who do continue to have seizures following treatment. To better identify candidates who are more likely to see benefits from undergoing iEEG, we investigated preoperative and iEEG peri-operative features associated with the localization of a putative SOZ, undergoing subsequent surgical treatment, and seizure outcomes.

METHODS

We conducted a retrospective cohort study of consecutive patients who underwent iEEG from 2001 to 2022 at two institutions. Outcomes included SOZ identification, proceeding to surgical treatment (resection vs. neuromodulation), and subsequent seizure freedom.

RESULTS

We identified 329 unique patients who were followed for a median of 3.9 (IQR:7) years, with a minimum of 2-year follow-up for seizure outcomes analyses. Multivariate analysis identified lateralized and lobar localization on scalp EEG (OR 3.8, p = 0.001) to be associated with SOZ localization. Patients with unilateral localization on scalp EEG (OR 3.0, p = 0.003), unilateral preimplantation hypothesis (OR 3.1, p = 0.001), and lesional preoperative MRI (OR 2.1, p = 0.033) were more likely to undergo resection than neuromodulation. Similarly, a unilateral pre-implantation hypothesis (OR 2.6, p < 0.001) favored seizure freedom, whereas prior neuromodulation (OR 0.3, p = 0.013) decreased the odds. Larger number of preoperative anti-seizure medications (ASMs) did not influence seizure freedom rates but did decrease favorable (Engel I, II) seizure outcomes (OR 0.7, p = 0.026).

INTERPRETATION

Non-invasive localization data prior to iEEG are associated with subsequent resection and seizure freedom, independent of iEEG localization. Factors predictive of SOZ localization are not necessarily predictive of post-operative seizure freedom.

Stereoelectroencephalography: a review of complications and outcomes in a new Australian centre

BACKGROUND

Surgical management of refractory focal epilepsy requires preoperative localisation of the epileptogenic zone (EZ). To augment noninvasive studies, stereoelectroencephalography (SEEG) is being increasingly adopted as a form of intracranial monitoring.

AIMS

This study aimed to determine the rate of complications for patients undergoing SEEG and to report the success of SEEG with regard to EZ detection and seizure outcome following definitive surgery.

METHODS

A retrospective cohort design investigated all cases of SEEG at our institution. Surgical, anaesthetic and medical complications with subsequent epilepsy surgery and seizure outcome data were extracted from medical records. Multivariate logistic regression was used to investigate the relationship between both the number of electrodes per patient and the duration of SEEG recording with the rate of complications.

RESULTS

Sixty-four patients with 66 implantations were included. Headache was the most common complication (n = 54, 82%). There were no major surgical or medical complications. Two anaesthetic complications occurred. EZ localisation was successful in 63 cases (95%). Curative intent surgery was performed in 39 patients (59%) and 23 patients achieved an Engel class I outcome (59% of those undergoing surgery). The number of electrodes and duration of recording were not associated with complications.

CONCLUSIONS

No patients in our series experienced major surgical or medical complications and we have highlighted the challenges associated with neuroanaesthesia in SEEG. Our complication rates and seizure outcomes are equivalent to published literature indicating that this technique can be successfully established in newer centres using careful case selection. Standardised reporting of SEEG complications should be adopted.

On the clinical utility of on-scalp MEG: A modeling study of epileptic activity source estimation

OBJECTIVE

Epilepsy surgery requires localization of the seizure onset zone (SOZ). Today this can only be achieved by intracranial electroencephalography (iEEG). The iEEG electrode placement is guided by findings from non-invasive modalities that cannot themselves detect SOZ-generated initial seizure activity. On scalp magnetoencephalography (osMEG), with sensors placed on the scalp, demonstrates higher sensitivity than conventional MEG (convMEG) and could potentially detect early seizure activity. Here, we modeled EEG, convMEG and osMEG to compare the modalities' ability to localize SOZ activity and to detect epileptic spikes.

METHODS

We modeled seizure propagation within ten epileptic networks located in the mesial and lateral temporal lobe; basal, dorsal, central and frontopolar frontal lobe; parietal and occipital lobe as well as insula and cingulum. The networks included brain regions often involved in focal epilepsy. 128-channel osMEG, convMEG, EEG and combined osMEG + EEG and convMEG + EEG were modeled, and the SOZ source estimation accuracy was quantified and compared using Student's t-test.

RESULTS

OsMEG was significantly (p-value <0.01) better than both convMEG and EEG at detecting the earliest SOZ-generated seizure activity and epileptic spikes, and better at localizing seizure activity from all epileptic networks (p < 0.01).

CONCLUSIONS

Our modeling results clearly show that osMEG has an unsurpassed potential to detect both epileptic spikes and seizure activity from all simulated anatomical sites.

SIGNIFICANCE

No clinically available non-invasive technique can detect SOZ activity from all brain regions. Our study indicates that osMEG has the potential to become an important clinical tool, improving both non-invasive SOZ localization and iEEG electrode placement accuracy.

Automated Identification of Stereoelectroencephalography Contacts and Measurement of Factors Influencing Accuracy of Frame Stereotaxy

OBJECTIVE

Stereoelectroencephalography (SEEG) is an established invasive diagnostic technique for use in patients with drug-resistant focal epilepsy evaluated before resective epilepsy surgery. The factors that influence the accuracy of electrode implantation are not fully understood. Adequate accuracy prevents the risk of major surgery complications. Precise knowledge of the anatomical positions of individual electrode contacts is crucial for the interpretation of SEEG recordings and subsequent surgery.

METHODS

We developed an image processing pipeline to localize implanted electrodes and detect individual contact positions using computed tomography (CT), as a substitute for time-consuming manual labeling. The algorithm automates measurement of parameters of the electrodes implanted in the skull (bone thickness, implantation angle and depth) for use in modeling of predictive factors that influence implantation accuracy.

RESULTS

Fifty-four patients evaluated by SEEG were analyzed. A total of 662 SEEG electrodes with 8,745 contacts were stereotactically inserted. The automated detector localized all contacts with better accuracy than manual labeling (p < 0.001). The retrospective implantation accuracy of the target point was 2.4 ± 1.1 mm. A multifactorial analysis determined that almost 58% of the total error was attributable to measurable factors. The remaining 42% was attributable to random error.

CONCLUSION

SEEG contacts can be reliably marked by our proposed method. The trajectory of electrodes can be parametrically analyzed to predict and validate implantation accuracy using a multifactorial model.

SIGNIFICANCE

This novel, automated image processing technique is a potentially clinically important, assistive tool for increasing the yield, efficiency, and safety of SEEG.

Stereoelectroencephalography Implantation Using Frameless Neuronavigation and Varioguide: Prospective Analysis of Accuracy and Safety in a Case Series of 11 Patients

BACKGROUND

Stereoencephalography (SEEG) is becoming a widespread diagnostic procedure for drug-resistant epilepsy investigation. Techniques include frame-based and robot-assisted implantation, and more recently, frameless neuronavigated systems (FNSs). Despite its recent use, the accuracy and safety of FNS are still under investigation.

OBJECTIVE

To assess in a prospective study the accuracy and safety of a specific FNS use for SEEG implantation.

METHODS

Twelve patients who underwent SEEG implantation using FNS (Varioguide [Brainlab]) were included in this study. Data were collected prospectively and included demographic data, postoperative complications, functional results, and implantation characteristics (i.e., duration and number of electrodes). Further analysis included accuracy at entry point and target using measurements of the euclidean distance between planned and actual trajectories.

RESULTS

Eleven patients underwent SEEG-FNS implantation from May 2019 to March 2020. One patient did not undergo surgery because of a bleeding disorder. The mean target deviation was 4.06 mm, and mean entry point deviation was 4.2 mm, with insular electrodes significantly more deviated. Results excluding insular electrodes showed a mean target deviation of 3.66 mm and a mean entry point deviation of 3.77 mm. No severe complications occurred; a few mild to moderate adverse events were reported (1 superficial infection, 1 seizure cluster, and 3 transient neurologic impairments). The mean implantation duration by electrodes was 18.5 minutes.

CONCLUSIONS

Implantation of depth electrodes for SEEG using FNS seems to be safe, but larger prospective studies are needed to validate these results. Accuracy is sufficient for noninsular trajectories but warrant caution for insular trajectories with statistically significantly less accuracy.

Sensing local field potentials with a directional and scalable depth electrode array

Objective. A variety of electrophysiology tools are available to the neurosurgeon for diagnosis, functional therapy, and neural prosthetics. However, no tool can currently address these three critical needs: (a) access to all cortical regions in a minimally invasive manner; (b) recordings with microscale, mesoscale, and macroscale resolutions simultaneously; and (c) access to spatially distant multiple brain regions that constitute distributed cognitive networks.Approach.We modeled, designed, and demonstrated a novel device for recording local field potentials (LFPs) with the form factor of a stereo-electroencephalographic electrode and combined with radially distributed microelectrodes.Main results. Electro-quasistatic models demonstrate that the lead body amplifies and shields LFP sources based on direction, enablingdirectional sensitivity andscalability, referred to as thedirectional andscalable (DISC) array.In vivo,DISC demonstrated significantly improved signal-to-noise ratio, directional sensitivity, and decoding accuracy from rat barrel cortex recordings during whisker stimulation. Critical for future translation, DISC demonstrated a higher signal to noise ratio (SNR) than virtual ring electrodes and a noise floor approaching that of large ring electrodes in an unshielded environment after common average referencing. DISC also revealed independent, stereoscopic current source density measures whose direction was verified after histology.Significance. Directional sensitivity of LFPs may significantly improve brain-computer interfaces and many diagnostic procedures, including epilepsy foci detection and deep brain targeting.

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.

Factors Predicting Outcome After Intracranial EEG Evaluation in Patients With Medically Refractory Epilepsy

BACKGROUND AND OBJECTIVES

The aim of this study was to identify predictors of a resective surgery and subsequent seizure freedom following intracranial EEG (ICEEG) for seizure-onset localization.

METHODS

This is a retrospective chart review of 178 consecutive patients with medically refractory epilepsy who underwent ICEEG monitoring from 2002 to 2015. Univariable and multivariable regression analysis identified independent predictors of resection vs other options. Stepwise Akaike information criteria with the aid of clinical consideration were used to select the best multivariable model for predicting resection and outcome. Discrete time survival analysis was used to analyze the factors predicting seizure-free outcome. Cumulative probability of seizure freedom was analyzed using Kaplan-Meier curves and compared between resection and nonresection groups. Additional univariate analysis was performed on 8 select clinical scenarios commonly encountered during epilepsy surgical evaluations.

RESULTS

Multivariable analysis identified the presence of a lesional MRI, presurgical hypothesis suggesting temporal lobe onset, and a nondominant hemisphere implant as independent predictors of resection (p < 0.0001, area under the receiver operating characteristic curve 0.80, 95% CI 0.73-0.87). Focal ICEEG onset and undergoing a resective surgery predicted absolute seizure freedom at the 5-year follow-up. Patients who underwent resective surgery were more likely to be seizure-free at 5 years compared with continued medical treatment or neuromodulation (60% vs 7%; p < 0.0001, hazard ratio 0.16, 95% CI 0.09-0.28). Even patients thought to have unfavorable predictors (nonlesional MRI or extratemporal lobe hypothesis or dominant hemisphere implant) had ≥50% chance of seizure freedom at 5 years if they underwent resection.

DISCUSSION

Unfavorable predictors, including having nonlesional extratemporal epilepsy, should not deter a thorough presurgical evaluation, including with invasive recordings in many cases. Resective surgery without functional impairment offers the best chance for sustained seizure freedom and should always be considered first.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that the presence of a lesional MRI, presurgical hypothesis suggesting temporal lobe onset, and a nondominant hemisphere implant are independent predictors of resection. Focal ICEEG onset and undergoing resection are independent predictors of 5-year seizure freedom.

Multimodal prognostic features of seizure freedom in epilepsy surgery

OBJECTIVE

Accurate preoperative predictions of seizure freedom following surgery for focal drug resistant epilepsy remain elusive. Our objective was to systematically evaluate all meta-analyses of epilepsy surgery with seizure freedom as the primary outcome, to identify clinical features that are consistently prognostic and should be included in the future models.

METHODS

We searched PubMed and Cochrane using free-text and Medical Subject Heading (MeSH) terms according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses. This study was registered on PROSPERO. We classified features as prognostic, non-prognostic and uncertain and into seven subcategories: 'clinical', 'imaging', 'neurophysiology', 'multimodal concordance', 'genetic', 'surgical technique' and 'pathology'. We propose a structural causal model based on these features.

RESULTS

We found 46 features from 38 meta-analyses over 22 years. The following were consistently prognostic across meta-analyses: febrile convulsions, hippocampal sclerosis, focal abnormal MRI, Single-Photon Emission Computed Tomography (SPECT) coregistered to MRI, focal ictal/interictal EEG, EEG-MRI concordance, temporal lobe resections, complete excision, histopathological lesions, tumours and focal cortical dysplasia type IIb. Severe learning disability was predictive of poor prognosis. Others, including sex and side of resection, were non-prognostic. There were limited meta-analyses investigating genetic contributions, structural connectivity or multimodal concordance and few adjusted for known confounders or performed corrections for multiple comparisons.

SIGNIFICANCE

Seizure-free outcomes have not improved over decades of epilepsy surgery and despite a multitude of models, none prognosticate accurately. Our list of multimodal population-invariant prognostic features and proposed structural causal model may serve as an objective foundation for statistical adjustments of plausible confounders for use in high-dimensional models.

PROSPERO REGISTRATION NUMBER

CRD42021185232.

[Stereoelectroencephalography (seeg): a brief historical review of modern deep electrode implantation methods used for diagnosis and treatment of epilepsy]

More than 30% of patients with symptomatic epilepsy are resistant to drug therapy and therefore surgical treatment is the method of choice for such patients. Search and localization of the epileptogenic zone and all parts of the neural networks involved in stereotypic seizures are the most important objectives of pre-surgical evaluation and the prerequisite for the successful surgery. In the last decade, stereotactic implantation of multiple intracerebral multi-contact electrodes (SEEG) has been increasingly used for this purpose. The article includes a brief history of SEEG and a description of the major techniques for stereotactic implantation of electrodes. Information on accuracy (errors and deviations from planned target) and on complications are summarized. The data on the clinical value of the method and how these data affected the results of subsequent treatment are highlighted. The method of thermocoagulation and its results are briefly considered.

Intracranial monitoring contributes to seizure freedom for temporal lobectomy patients with nonconcordant preoperative data

Objective

The question of whether a patient with presumed temporal lobe seizures should proceed directly to temporal lobectomy surgery versus undergo intracranial monitoring arises commonly. We evaluate the effect of intracranial monitoring on seizure outcome in a retrospective cohort of consecutive subjects who specifically underwent an anterior temporal lobectomy (ATL) for refractory temporal lobe epilepsy (TLE).

Methods

We performed a retrospective analysis of 85 patients with focal refractory TLE who underwent ATL following: (a) intracranial monitoring via craniotomy and subdural/depth electrodes (SDE/DE), (b) intracranial monitoring via stereotactic electroencephalography (sEEG), or (c) no intracranial monitoring (direct ATL—dATL). For each subject, the presurgical primary hypothesis for epileptogenic zone localization was characterized as unilateral TLE, unilateral TLE plus (TLE+), or TLE with bilateral/poor lateralization.

Results

At one‐year and most recent follow‐up, Engel Class I and combined I/II outcomes did not differ significantly between the groups. Outcomes were better in the dATL group compared to the intracranial monitoring groups for lesional cases but were similar in nonlesional cases. Those requiring intracranial monitoring for a hypothesis of TLE+had similar outcomes with either intracranial monitoring approach. sEEG was the only approach used in patients with bilateral or poorly lateralized TLE, resulting in 77.8% of patients seizure‐free at last follow‐up. Importantly, for 85% of patients undergoing SEEG, recommendation for ATL resulted from modifying the primary hypothesis based on iEEG data.

Significance

Our study highlights the value of intracranial monitoring in equalizing seizure outcomes in difficult‐to‐treat TLE patients undergoing ATL.

Stereotactic depth electrode placement surgery in paediatric and adult patients with the Neuromate robotic device: Accuracy, complications and epileptological results

OBJECTIVE

The number of patients requiring depth electrode implantation for invasive video EEG diagnostics increases in most epilepsy centres. Here we report on our institutional experience with frameless robot-assisted stereotactic placement of intracerebral depth electrodes using the Neuromate® stereotactic robot-system.

METHODS

We identified all patients who had undergone robot-assisted stereotactic placement of intracerebral depth electrodes for invasive extra-operative epilepsy monitoring between September 2013 and March 2020. We studied technical (placement) and diagnostic accuracy of the robot-assisted procedure, associated surgical complications and procedural time requirements.

RESULTS

We evaluated a total of 464 depth electrodes implanted in 74 patients (mean 6 per patient, range 1-12). There were 27 children and 47 adults (age range: 3.6-64.6 yrs.). The mean entry and target point errors were 1.82±1.15 and 1.98±1.05 mm. Target and entry point errors were significantly higher in paediatric vs. adult patients and for electrodes targeting the temporo-mesial region. There were no clinically relevant haemorrhages and no infectious complications. Mean time for the placement of one electrode was 37±14 min and surgery time per electrode decreased with the number of electrodes placed. 55 patients (74.3%) underwent definitive surgical treatment. 36/51 (70.1%) patients followed for >12 months or until seizure recurrence became seizure-free (ILAE I).

CONCLUSION

Frameless robot-guided stereotactic placement of depth electrodes with the Neuromate® stereotactic robot-system is safe and feasible even in very young children, with good in vivo accuracy and high diagnostic precision. The surgical workflow is time-efficient and further improves with increasing numbers of implanted electrodes.

All that glitters: Contribution of stereo-EEG in patients with lesional epilepsy

OBJECTIVE

To determine the contribution of stereo-EEG for localization purpose in patients with a visible lesion on MRI.

BACKGROUND

Intracranial EEG is often used to localize the epileptogenic focus in patients with non-lesional focal epilepsy. Its role in cases where a lesion is visible on MRI can be even more complex and the relationship between the lesion and the seizure onset has rarely been addressed.

METHODS

All consecutive patients between February 2013 and May 2018 who underwent stereo-EEG and had a lesion visible on MRI were included. We assessed the localization of the seizure onset and its relationship with the lesion. Clinical, radiological, and electrographic analyses were performed.

RESULTS

Stereo-EEG revealed a seizure onset with either partial or no overlap with the lesion seen on MRI in 42 (56 %) of the 75 lesions included. Mesial temporal sclerosis was the only lesion type associated with an exclusively lesional seizure onset (p = 0.003).

CONCLUSION

Epilepsy surgery in MRI-positive cases should rely not only the results of lesions seen on MRI, which might be potentially misleading; SEEG is a gold standard method in these cases to define resective borders.

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.

Resting-state functional magnetic resonance imaging with independent component analysis for presurgical seizure onset zone localization: A systematic review and meta-analysis

OBJECTIVE

One of the greatest challenges of achieving successful surgical outcomes in patients with epilepsy is the ability to properly localize the seizure onset zone (SOZ). Many techniques exist for localizing the SOZ, including intracranial electroencephalography, magnetoencephalography, and stereoelectroencephalography. Recently, resting-state functional magnetic resonance imaging (rs-fMRI) in conjunction with independent component analysis (ICA) has been utilized for presurgical planning of SOZ resection, with varying results. In this meta-analysis, we analyze the current role of rs-fMRI in identifying the SOZ for presurgical planning for patients with drug-resistant epilepsy. Specifically, we seek to demonstrate its current effectiveness compared to other methods of SOZ localization.

METHODS

A literature review was conducted using the PubMed, MEDLINE, and Embase databases up to May of 2020. A total of 253 articles were screened, and seven studies were chosen for analysis. Each study was analyzed for SOZ localization by ground truth, SOZ localization by rs-fMRI with ICA, principal component analysis, or intrinsic connectivity contrast, and outcomes of surgery. A meta-analysis was performed to analyze how ground truth compares to rs-fMRI in SOZ localization.

RESULTS

The odds ratio comparing ground truth to rs-fMRI was 2.63 (95% confidence interval = 0.66-10.56). Average concordance of rs-fMRI SOZ localization compared with ground truth localization across studies was 71.3%.

SIGNIFICANCE

In the hunt for less invasive presurgical planning for epilepsy surgery, rs-fMRI with ICA provides a promising avenue for future standard practice. Our preliminary results show no significant difference in surgical outcomes between traditional standards of SOZ localization and rs-fMRI with ICA. We believe that rs-fMRI could be a step forward in this search. Further investigation comparing rs-fMRI to traditional methods of SOZ localization should be conducted, with the hope of moving toward relying solely on noninvasive screening methods.

Stereoelectroencephalography Versus Subdural Strip Electrode Implantations: Feasibility, Complications, and Outcomes in 500 Intracranial Monitoring Cases for Drug-Resistant Epilepsy

BACKGROUND

Both stereoelectroencephalography (SEEG) and subdural strip electrodes (SSE) are used for intracranial electroencephalographic recordings in the invasive investigation of patients with drug-resistant epilepsy.

OBJECTIVE

To compare SEEG and SSE with respect to feasibility, complications, and outcome in this single-center study.

METHODS

Patient characteristics, periprocedural parameters, complications, and outcome were acquired from a pro- and retrospectively managed databank to compare SEEG and SSE cases.

RESULTS

A total of 500 intracranial electroencephalographic monitoring cases in 450 patients were analyzed (145 SEEG and 355 SSE). Both groups were of similar age, gender distribution, and duration of epilepsy. Implantation of each SEEG electrode took 13.9 ± 7.6 min (20 ± 12 min for each SSE; P &lt; .01). Radiation exposure to the patient was 4.3 ± 7.7 s to a dose area product of 14.6 ± 27.9 rad*cm2 for SEEG and 9.4 ± 8.9 s with 21 ± 22.4 rad*cm2 for SSE (P &lt; .01). There was no difference in the length of stay (12.2 ± 7.2 and 12 ± 6.3 d). The complication rate was low in both groups. No infections were seen in SEEG cases (2.3% after SSE). The rate of hemorrhage was 2.8% for SEEG and 1.4% for SSE. Surgical outcome was similar.

CONCLUSION

SEEG allows targeting deeply situated foci with a non-inferior safety profile to SSE and seizure outcome comparable to SSE.

Patient phenotypes and clinical outcomes in invasive monitoring for epilepsy: An individual patient data meta-analysis

OBJECTIVE

Invasive monitoring provides valuable clinical information in patients with drug-resistant epilepsy (DRE). However, there is no clear evidence indicating either stereoelectroencephalography (SEEG) or subdural electrodes (SDE) as the optimal method. Our goal was to examine differences in postresection seizure freedom rates between SEEG- and SDE-informed resective epilepsy surgeries. Additionally, we aimed to determine potential clinical indicators for SEEG or SDE monitoring in patients with drug-resistant epilepsy.

METHODS

A systematic literature review was performed in which we searched for primary articles using keywords such as "electroencephalography", "intracranial grid", and "epilepsy." Only studies containing individual patient data (IPD) were included for analysis. A one-stage IPD meta-analysis was performed to determine differences in rates of seizure freedom (International League Against Epilepsy (ILAE) guidelines and Engel classification) and resection status between SEEG and SDE patients. A Cox proportional-hazards regression was performed to determine the effect of time on seizure freedom status. Additionally, a principal component analysis was performed to investigate primary drivers of variance between these two groups.

RESULTS

This IPD meta-analysis compared differences between SEEG and SDE invasive monitoring techniques in 595 patients from 33 studies. Our results demonstrate that while there was no difference in seizure freedom rates regardless of resection (p = 0.0565), SEEG was associated with a lower rate of resection compared with SDE (82.00% SEEG, 92.74% SDE, p = 0.0002). Additionally, while SDE was associated with a higher rate of postresection seizure freedom (54.04% SEEG, 64.32% SDE, p = 0.0247), the difference between seizure freedom rates following SEEG- or SDE-informed resection decreased with long-term follow-up. A principal component analysis showed that cases resulting in SEEG were associated with lower risk of morbidity than SDE cases, which were strongly collinear with multiple subpial transections, anterior temporal lobectomy, amygdalectomy, and hippocampectomy.

SIGNIFICANCE

In this IPD meta-analysis of SEEG and SDE invasive monitoring techniques, SEEG and SDE were associated with similar rates of seizure freedom at latest follow-up. The former was associated with lower rates of resection. Furthermore, the clinical phenotypes of patients undergoing SEEG monitoring was associated with lower rates of complications. Future long-term prospective registries of IPD are promising options for clarifying the differences in these intracranial monitoring techniques as well as the unique patient phenotypes that may be associated with their indication.