Depth electrodes in pediatric epilepsy surgery

Smaller Knife, Fewer Seizures? Recent Advances in Minimally Invasive Techniques in Pediatric Epilepsy Surgery

Children with drug-resistant epilepsy are at high risk for developmental delay, increased mortality, psychiatric comorbidities, and requiring assistance with activities of daily living. Despite the advent of new and effective pharmacologic therapies, about one in 5 children will develop drug-resistant epilepsy, and most of these children continue to have seizures despite trials of other medication. Epilepsy surgery is often a safe and effective option which may offer seizure freedom or at least a significant reduction in seizure burden in many children. However, despite published evidence of safety and efficacy, epilepsy surgery remains underutilized in the pediatric population. Patient and family fears about the risks of surgery may contribute to this gap. Less invasive surgical techniques may be more palatable to children with epilepsy and their caregivers. In this review, we present recent advances in minimally invasive techniques for the surgical treatment of epilepsy as well as intriguing possibilities for the future. We describe the indications for, benefits of, and limits to minimally-invasive techniques including Stereo-encephalography, laser interstitial thermal ablation, deep brain stimulation, focused ultrasound, stereo-encephalography-guided radiofrequency ablation, endoscopic disconnections, and responsive neurostimulation.

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.

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.

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.

Method of invasive monitoring in epilepsy surgery and seizure freedom and morbidity: A systematic review

OBJECTIVE

Invasive monitoring is sometimes necessary to guide resective surgery in epilepsy patients, but the ideal method is unknown. In this systematic review, we assess the association of postresection seizure freedom and adverse events in stereoelectroencephalography (SEEG) and subdural electrodes (SDE).

METHODS

We searched three electronic databases (MEDLINE, Embase, and CENTRAL [Cochrane Central Register of Controlled Trials]) from their inception to January 2018 with the keywords "electroencephalography," "intracranial grid," and "epilepsy." Studies that presented primary quantitative patient data for postresection seizure freedom with at least 1 year of follow-up or complication rates of SEEG- or SDE-monitored patients were included. Two trained investigators independently collected data from eligible studies. Weighted mean differences (WMDs) with 95% confidence interval (CIs) were used as a measure of the association of SEEG or SDE with seizure freedom and with adverse event outcomes.

RESULTS

Of 11 462 screened records, 48 studies met inclusion criteria. These studies reported on 1973 SEEG patients and 2036 SDE patients. Our systematic review revealed SEEG was associated with 61.0% and SDE was associated with 56.4% seizure freedom after resection (WMD = +5.8%, 95% CI = 4.7-6.9%, P = .001). Furthermore, SEEG was associated with 4.8% and SDE was associated with 15.5% morbidity (WMD = -10.6%, 95% CI = -11.6 to -9.6%, P = .001). SEEG was associated with 0.2% mortality and SDE was associated with 0.4% mortality (WMD = -0.2%, 95% CI = -0.3 to -0.1%, P = .001).

SIGNIFICANCE

In this systematic review of SEEG and SDE invasive monitoring techniques, SEEG was associated with fewer surgical resections yet better seizure freedom outcomes in those undergoing resections. SEEG was also associated with lower mortality and morbidity than SDE. Clinical studies directly comparing these modalities are necessary to understand the relative rates of seizure freedom, morbidity, and mortality associated with these techniques.

Robot-assisted stereoelectroencephalography in children

OBJECTIVEThe goal in the study was to describe the clinical outcomes associated with robot-assisted stereoelectroencephalography (SEEG) in children.METHODSThe authors performed a retrospective, single-center study in consecutive children with medically refractory epilepsy who were undergoing robot-assisted SEEG. Kaplan-Meier survival analysis was used to calculate the probability of seizure freedom. Both univariate and multivariate methods were used to analyze the preoperative and operative factors associated with seizure freedom.RESULTSFifty-seven children underwent a total of 64 robot-assisted procedures. The patients' mean age was 12 years, an average of 6.4 antiepileptic drugs (AEDs) per patient had failed prior to implantation, and in 56% of the patients the disease was considered nonlesional. On average, children had 12.4 electrodes placed per implantation, with an implantation time of 9.6 minutes per electrode and a 10-day postoperative stay. SEEG analysis yielded a definable epileptogenic zone in 51 (89%) patients; 42 (74%) patients underwent surgery, half of whom were seizure free at last follow-up, 19.6 months from resection. In a multivariate generalized linear model, resective surgery, older age, and shorter SEEG-related hospital length of stay were associated with seizure freedom. In a Cox proportional hazards model including only the children who underwent resective surgery, older age was the only significant factor associated with seizure freedom. Complications related to bleeding were the major contributors to morbidity. One patient (1.5%) had a symptomatic hemorrhage resulting in a permanent neurological deficit.CONCLUSIONSThe authors report one of the largest pediatric-specific SEEG series demonstrating that the modern surgical management of medically refractory epilepsy in children can lead to seizure freedom in many patients, while also highlighting the challenges posed by this difficult patient population.

Risk analysis of hemorrhage in stereo-electroencephalography procedures

OBJECTIVE

To examine the true incidence of hemorrhage related to stereo-electroencephalography (SEEG) procedures. To analyze risk factors associated with the presence of different types of hemorrhage in SEEG procedures.

METHODS

This was a retrospective, single-center observational study examining every SEEG implantation performed at our center from 2009 to 2017. This consisted of 549 consecutive SEEG implantations using a variety of stereotactic and imaging techniques. A hemorrhage grading system was applied by a blinded neuroradiologist to every postimplant and postexplant computed tomography (CT) scan. Hemorrhages were classified as asymptomatic or symptomatic based on neurologic deficit seen on examination. Statistical analysis included multivariate regression using relevant preoperative variables to predict the presence of hemorrhage.

RESULTS

One hundred five implantations (19.1%) had any type of hemorrhage seen on postimplant CT. Of these, 93 (16.9%) were asymptomatic and 12 (2.2%) were symptomatic, with 3 implantations (0.6%) resulting in either a permanent deficit (2, 0.4%) or death (1, 0.2%). Male sex, increased number of electrodes, and increasing age were associated with increased risk of postimplant hemorrhage on multivariate analysis. Increasing score in the grading system was related to a statistically significant increase in the likelihood of a symptomatic hemorrhage.

SIGNIFICANCE

Detailed examination of every postimplant CT reveals that the total hemorrhage rate appears higher than previously reported. Most of these hemorrhages are small and asymptomatic. Our grading system may be useful to risk stratify these hemorrhages and awaits prospective validation.

Extratemporal resections in pediatric epilepsy surgery-an overview

Despite optimized medical treatment, approximately one third of all patients with epilepsy continue to have seizures and by definition have medically resistant epilepsy (MRE). For these patients, surgical disruption of the epileptogenic network may enable freedom or great improvement in control of their seizures. The success of surgery is dependent on accurate localization of the epileptogenic zone and network. Epilepsy arising from regions of cortical dysplasia within the neocortex of the frontal, parietal, and occipital lobes show a propensity for reorganization and progressive decline in seizure freedom and consequent poorer surgical outcome. These procedures often require staged investigation with intracranial electrodes via subdural grids or stereoelectroencephalography (SEEG) and are considered extratemporal resections (ETRs). Central concepts include the following: (1) localization of epileptogenic and eloquent functional regions, (2) safe and effective placement of intracranial electrode arrays, (3) resection of epileptogenic cortex, and (4) avoidance of complications. Each of these concepts is summarized and developed in this summary paper.

Preoperative evaluation and surgical decision-making in pediatric epilepsy surgery

Epilepsy is a common disease in the pediatric population, and the majority of cases are controlled with medications and lifestyle modification. For the children whose seizures are pharmacoresistant, continued epileptic activity can have a severely detrimental impact on cognitive development. Early referral of children with drug-resistant seizures to a pediatric epilepsy surgery center for evaluation is critical to achieving optimal patient outcomes. There are several components to a thorough presurgical evaluation, including a detailed medical history and physical examination, noninvasive testing including electroencephalogram, magnetic resonance imaging (MRI) of the brain, and often metabolic imaging. When necessary, invasive diagnostic testing using intracranial monitoring can be used. The identification of an epileptic focus may allow resection or disconnection from normal brain structures, with the ultimate goal of complete seizure remission. Additional operative measures can decrease seizure frequency and/or intensity if a clear epileptic focus cannot be identified. In this review, we will discuss the nuances of presurgical evaluation and decision-making in the management of children with drug-resistant epilepsy (DRE).

Exploring human epileptic activity at the single-neuron level

Today, localization of the seizure focus heavily relies on EEG monitoring (scalp or intracranial). However, current technology enables much finer resolutions. The activity of hundreds of single neurons in the human brain can now be simultaneously explored before, during, and after a seizure or in association with an interictal discharge. This technology opens up new horizons to understanding epilepsy at a completely new level. This review therefore begins with a brief description of the basis of the technology, the microelectrodes, and the setup for their implantation in patients with epilepsy. Using these electrodes, recent studies provide novel insights into both the time domain and firing patterns of epileptic activity of single neurons. In the time domain, seizure-related activity may occur even minutes before seizure onset (in its current, EEG-based definition). Seizure-related neuronal interactions exhibit complex heterogeneous dynamics. In the seizure-onset zone, changes in firing patterns correlate with cell loss; in the penumbra, neurons maintain their spike stereotypy during a seizure. Hence, investigation of the extracellular electrical activity is expected to provide a better understanding of the mechanisms underlying the disease; it may, in the future, serve for a more accurate localization of the seizure focus; and it may also be employed to predict the occurrence of seizures prior to their behavioral manifestation in order to administer automatic therapeutic interventions.

Epilepsy surgery failure in children: a quantitative and qualitative analysis

OBJECT

Resection is a safe and effective treatment option for children with pharmacoresistant focal epilepsy, but some patients continue experience seizures after surgery. While most studies of pediatric epilepsy surgery focus on predictors of postoperative seizure outcome, these factors are often not modifiable, and the reasons for surgical failure may remain unclear.

METHODS

The authors performed a retrospective cohort study of children and adolescents who received focal resective surgery for pharmacoresistant epilepsy. Both quantitative and qualitative analyses of factors associated with persistent postoperative seizures were conducted.

RESULTS

Records were reviewed from 110 patients, ranging in age from 6 months to 19 years at the time of surgery, who underwent a total of 115 resections. At a mean 3.1-year follow-up, 76% of patients were free of disabling seizures (Engel Class I outcome). Seizure freedom was predicted by temporal lobe surgery compared with extratemporal resection, tumor or mesial temporal sclerosis compared with cortical dysplasia or other pathologies, and by a lower preoperative seizure frequency. Factors associated with persistent seizures (Engel Class II-IV outcome) included residual epileptogenic tissue adjacent to the resection cavity (40%), an additional epileptogenic zone distant from the resection cavity (32%), and the presence of a hemispheric epilepsy syndrome (28%).

CONCLUSIONS

While seizure outcomes in pediatric epilepsy surgery may be improved by the use of high-resolution neuroimaging and invasive electrographic studies, a more aggressive resection should be considered in certain patients, including hemispherectomy if a hemispheric epilepsy syndrome is suspected. Family counseling regarding treatment expectations is critical, and reoperation may be warranted in select cases.

Intracranial electroencephalography with subdural and/or depth electrodes in children with epilepsy: techniques, complications, and outcomes

Intracranial electroencephalographic monitoring with subdural and/or depth electrodes is widely used for the surgical localization of epileptic foci in patients with intractable partial epilepsy; however, data on safety and surgical outcome with this technique are still inadequate. The aims of this study were to assess the morbidity of intracranial recordings and the surgical outcomes in epileptic children. We retrospectively reviewed the clinical data for 137 children with epilepsy (mean age at implantation: 12.6 ± 3.8 years) who underwent intracranial monitoring with the implantation of strip or grid subdural electrodes and/or intracerebral depth electrodes from September 2004 to September 2011 at a tertiary epilepsy center in China. Complications were classified using five grades of severity (including mortality) and were further classified as either minor or severe. Outcome was classified according to Engel's classification. Regression analysis was performed to identify risk factors for complications. The mean duration of implantation was 5.3 ± 1.3 days. Among the 133 patients who underwent resection, 65 (48.9%) were seizure free (Engel Class I) at last known follow-up, which was >2 years after surgery for all patients. Also, 31 (23.3%) patients had a significant reduction in seizures (Engel Class II). Complications of any type were documented in 29 (21.7%) patients; 15 of these patients had intracranial hematoma. The results of multivariate analysis showed that the only independent risk factor for intracranial hematoma was number of electrode contacts. The most common pathologic diagnosis was focal cortical dysplasia (n=58). Our results showed that intracranial electroencephalographic monitoring in children provides good surgical outcomes and the level of risk is acceptable. When using this technique strategies such as using as few electrode contacts as possible should be adopted to minimize the risk of intracranial hematoma.