Deep Brain Stimulation for Refractory Focal Epilepsy: Unraveling the Insertional Effect up to Five Months Without Stimulation

INTRODUCTION

Following electrode implantation, a subgroup of patients treated with deep brain stimulation (DBS) for focal epilepsy exhibits a reduction of seizure frequency before stimulation is initiated. Microlesioning of the target structure has been postulated to be the cause of this "insertional" effect (IE). We examined the occurrence and duration of this IE in a group of patients with focal epilepsy following electrode implantation in the anterior nuclei of the thalamus (ANT) and/or nucleus accumbens (NAC) for DBS treatment.

MATERIALS AND METHODS

Changes in monthly seizure frequency compared to preoperative baseline were assessed one month (14 patients) and five months (four patients) after electrode implantation. A group analysis between patients with implantation of bilateral ANT-electrodes (four patients), NAC-electrodes (one patient) as well as ANT and NAC-electrodes (nine patients) was performed.

RESULTS

In this cohort, seizure frequency decreased one month after electrode implantation by 57.1 ± 30.1%, p ≤ 0.001 (compared to baseline). No significant difference within stimulation target subcohorts was found (p > 0.05). Out of the four patients without stimulation for five months following electrode insertion, three patients showed seizure frequency reduction lasting two to three months, while blinded to their stimulation status.

CONCLUSION

An IE might explain seizure frequency reduction in our cohort. This effect seems to be independent of the number of implanted electrodes and of the target itself. The time course of the blinded subgroup of epilepsy patients suggests a peak of the lesional effect at two to three months after electrode insertion.

Neuromodulation of the anterior thalamic nucleus as a therapeutic option for difficult-to-control epilepsy

Deep brain stimulation (DBS) consists of the electrical stimulation of the subcortical structures by implanting electrodes connected to a pulse generator. The thalamus, being a structure that has multiple connections with various parts of the central nervous system, is a suitable target for DBS. The anterior thalamic nucleus (ANT) serves as an important relay site for the limbic system by receiving input from the hippocampus and mammillary bodies, and sending input to the cingulate gyrus; thus forming the Papez circuit. Due to these connections, the ANT constitutes an ideal route for the propagation of epileptogenic activity. ANT-DBS has excellent results in the control of complex partial seizures. The vast majority of patients with ANT-DBS have shown a significant reduction in the frequency of their seizures of more than 50%.

Anatomical connectivity and efficacy of electro-therapy for seizure control: A SANTE's single-center regression analyses

OBJECTIVE

To assess based on a single-center data from a multicenter trial (Stimulation of the Anterior Nucleus for the Thalamus for Epilepsy (SANTE)), the role of anatomical connectivity and other factors (e.g., stimulating electrode placement) on efficacy of electro-therapy of the anterior thalamic nuclei (ATN), a node in Papez network, on pharmaco-resistant seizures.

DATA SOURCE

Adults with at least 6 seizures /month were enrolled in this trial. Percent seizure reduction was compared between subjects with seizures emerging inside Papez's network (IPN) to those with seizures outside it (OPN). Statistical analyses were performed on the first year of the trial.

RESULTS

Data from 11 subjects were analyzed. At Year 1, median seizure reduction was 80.5% (-100% to -40.3%) in 8/11 subjects with seizures IPN, vs. 52.8% (-61.4% to -23.7%) for 3/11 subjects with seizures OPN (2-sided Wilcoxon p = 0.08). At year 7, 3/11 subjects with seizures IPN had been seizure free for several years vs. 0/11 subjects with seizures OPN. Addition of 4 subjects from a pilot trial with nearly identical protocol to SANTE's, increased to 12/15 the number of subjects with seizures IPN. A 2-sided Fisher's exact test applied to seizure frequency reduction in the 12/15 cohort compared to the 3/15 with seizures OPN, showed significant (p = 0.04) differences in efficacy at the 70% seizure reduction rate. Median quality of life (QOL) scores for subjects with seizures IPN improved by 81% vs. 53% for subjects with seizures OPN. No other factors (e.g., current intensity) had a statistically significant effect on efficacy.

CONCLUSIONS

Degree of anatomical connectivity between stimulation targets and epileptogenic networks (ENs) plays an important role in therapeutic efficacy. This may be explained by the minimization of signal attenuation inherent in impulse transmission in nervous tissue partly as a function of fiber tract length, tissue anisotropy, and number of synaptic relays between stimulation target and epileptogenic networks.

Deep Brain Stimulation in Epilepsy: A Role for Modulation of the Mammillothalamic Tract in Seizure Control?

BACKGROUND

Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) can improve seizure control for patients with drug-resistant epilepsy (DRE). Yet, one cannot overlook the high discrepancy in efficacy among patients, possibly resulting from differences in stimulation site.

OBJECTIVE

To test the hypothesis that stimulation at the junction of the ANT and mammillothalamic tract (ANT-MTT junction) increases seizure control.

METHODS

The relationship between seizure control and the location of the active contacts to the ANT-MTT junction was investigated in 20 patients treated with ANT-DBS for DRE. Coordinates and Euclidean distance of the active contacts relative to the ANT-MTT junction were calculated and related to seizure control. Stimulation sites were mapped by modelling the volume of tissue activation (VTA) and generating stimulation heat maps.

RESULTS

After 1 yr of stimulation, patients had a median 46% reduction in total seizure frequency, 50% were responders, and 20% of patients were seizure-free. The Euclidean distance of the active contacts to the ANT-MTT junction correlates to change in seizure frequency (r2 = 0.24, P = .01) and is ∼30% smaller (P = .015) in responders than in non-responders. VTA models and stimulation heat maps indicate a hot-spot at the ANT-MTT junction for responders, whereas non-responders had no evident hot-spot.

CONCLUSION

Stimulation at the ANT-MTT junction correlates to increased seizure control. Our findings suggest a relationship between the stimulation site and therapy response in ANT-DBS for epilepsy with a potential role for the MTT. DBS directed at white matter merits further exploration for the treatment of epilepsy.

Probabilistic Mapping of Deep Brain Stimulation: Insights from 15 Years of Therapy

Deep brain stimulation (DBS) depends on precise delivery of electrical current to target tissues. However, the specific brain structures responsible for best outcome are still debated. We applied probabilistic stimulation mapping to a retrospective, multidisorder DBS dataset assembled over 15 years at our institution (n_total = 482 patients; n_{Parkinson disease} = 303; n_dystonia = 64; n_tremor = 39; n_{treatment-resistant depression/anorexia nervosa} = 76) to identify the neuroanatomical substrates of optimal clinical response. Using high-resolution structural magnetic resonance imaging and activation volume modeling, probabilistic stimulation maps (PSMs) that delineated areas of above-mean and below-mean response for each patient cohort were generated and defined in terms of their relationships with surrounding anatomical structures. Our results show that overlap between PSMs and individual patients' activation volumes can serve as a guide to predict clinical outcomes, but that this is not the sole determinant of response. In the future, individualized models that incorporate advancements in mapping techniques with patient-specific clinical variables will likely contribute to the optimization of DBS target selection and improved outcomes for patients. ANN NEUROL 2021;89:426-443.

Effects of anterior thalamic nuclei stimulation on gene expression in a rat model of temporal lobe epilepsy

Deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) has been shown to be effective and safe in the long-term treatment of refractory epilepsy. However, the mechanisms by which ANT-DBS controls epilepsy at the gene expression level (e.g., which regulatory mechanisms are altered) is not well understood. Nine rats were randomly assigned to the control group, the kainic acid (KA) group, and the DBS group. Temporal lobe epilepsy in rats was induced by a stereotaxic KA injection (KA group). The DBS group received the KA injection followed by treatment with ANT-DBS. Video-electroencephalogram (EEG) was used to monitor seizures. Total RNA samples were isolated from the hippocampus of three groups. Microarray was used to detect differentially regulated mRNAs. GO and pathway analysis were performed to analyze the functional categories and affected pathways. qPCR was used to prove the reliability of the microarray results. The differentially expressed genes the KA group and the DBS group, relative to the control group, were screened and a total of 2910 genes were identified. These genes were involved in functional categories such as ion channel activity (P = 5.01 × 10^-8), gated channel activity (P = 1.42 × 10^-7), lipid binding (P = 4.97 × 10^-5), and hydrolase activity (P = 5.02 × 10^-5) and pathways such as calcium signaling pathway (P = 2.09 × 10^-8), glutamatergic synapse (P = 4.09 × 10^-8) and NOD-like receptor signaling pathway (P = 2.70 × 10^-6). Differentially expressed mRNAs might play a role in the pathogenesis of temporal lobe epilepsy. Calcium signaling pathways, synaptic glutamate, and NOD-like receptor signaling pathway play a central role in normal-epilepsy-ANT-DBS treatment series. ANT-DBS achieves its antiepileptic effects by modulating target genes involved in a variety of functions and pathways.

Stimulation of the Anterior Nucleus of the Thalamus for Epilepsy: A Canadian Experience

OBJECTIVE

To describe the experience with Anterior Nucleus of the Thalamus-Deep Brain Stimulation (ANT-DBS) for the treatment of epilepsy at a Canadian Center.

METHODS

All patients who underwent ANT-DBS implantation between 2013 (first patient implanted at our center) and 2020 were included. These patients had therapy-resistant epilepsy (TRE), were not candidates for resective surgery, and failed vagus nerve stimulation (VNS) treatment. Baseline of monthly seizure frequency was calculated within 3 months prior to VNS placement. Monthly seizure frequency was assessed at different points along the timeline: 3 months before ANT-DBS implantation as well as 3, 6, 12, 24, 36, 48, 60, and 72 months after ANT-DBS device placement. At each time point, seizure frequency was compared to baseline.

RESULTS

Six patients were implanted with ANT-DBS. Three (50%) patients had multifocal epilepsy, one (16.6%) had focal epilepsy, and two (33.4%) had combined generalized and focal epilepsy. Two patients with multifocal epilepsy experienced a seizure reduction >50% in the long-term follow-up. Three (50%) patients did not showed improvement: two with combined generalized and focal epilepsy and one with focal epilepsy. There were not surgical or device-related side effects. Two (33.3%) patients presented mild and transient headaches as a stimulation-related side effect.

CONCLUSION

ANT-DBS is an effective and safe treatment for focal TRE. Our experience suggests that patients with multifocal epilepsy due to regional lesion may benefit from ANT-DBS the most. Further investigations are required to determine optimal parameters of stimulation.

European Expert Opinion on ANT-DBS therapy for patients with drug-resistant epilepsy (a Delphi consensus)

INTRODUCTION

Although deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS) represents an established third-line therapy for patients with drug-resistant focal epilepsy, guiding reports on practical treatment principles remain scarce.

METHODS

An Expert Panel (EP) of 10 European neurologists and 4 neurosurgeons was assembled to share their experience with ANT-DBS therapy. The process included a review of the current literature, which served as a basis for an online survey completed by the EP prior to and following a face-to-face meeting (Delphi method). An agreement level of ≥71 % was considered as consensus.

RESULTS

Out of 86 reviewed studies, 46 (53 %) were selected to extract information on the most reported criteria for patient selection, management, and outcome. The Delphi process yielded EP consensus on 4 parameters for selection of good candidates and patient management as well as 7 reasons of concern for this therapy. Since it was not possible to give strict device programming advice due to low levels of evidence, the experts shared their clinical practice: all of them start with monopolar stimulation, 79 % using the cycling mode. Most (93 %) EP members set the initial stimulation frequency and pulse width according to the SANTE parameters, while there is more variability in the amplitudes used. Further agreement was achieved on a list of 7 patient outcome parameters to be monitored during the follow-up.

CONCLUSIONS

Although current evidence is too low for definite practical guidelines, this EP report could support the selection and management of patients with ANT-DBS.

Improving the effectiveness of ANT DBS therapy for epilepsy with optimal current targeting

OBJECTIVE

Deep brain stimulation of the ANT is a novel treatment option in refractory epilepsy with an established efficacy at the group level. However, data on the effect of individualized programming are currently lacking. We report the effect of programming changes on outcome in deep brain stimulation of anterior nucleus of thalamus (ANT DBS). Secondly, we investigated whether the effect differs between seizure types. Thirdly, we compared the response status between patients with stimulation contacts verified inside the ANT with patients with contacts located outside of ANT.

METHODS

The participants were 27 consecutive patients with ANT DBS implantation with at least two-year follow-up. Seizures were subdivided into focal aware (FAS), focal impaired awareness (FIAS), and focal to bilateral tonic-clonic seizures (FBTCS). The patients' seizure diaries were analyzed retrospectively to assess changes in different seizure types. Active contact locations for each patient were verified from preoperative MRI and postoperative CT fusion images using SureTune III (Medtronic Inc, Minneapolis, MN) software.

RESULTS

A significant reduction in monthly mean seizure frequency occurred in FIAS: 56% at two-year and 65% at five-year follow-up. The effects on FAS and FBTCS were less pronounced. Patients with contacts inside the ANT or on the anterolateral border of ANT experienced a greater reduction in seizure frequency than patients with outside-ANT contacts. Ultimately, seven patients became responders due to changes in DBS programming or repositioning of contacts, increasing our responder rate from 44% to 70% as measured by a seizure reduction of at least 50%.

SIGNIFICANCE

ANT DBS appears to be especially effective in reducing FIAS, when the appropriately chosen contacts are activated.

Anterior thalamic deep brain stimulation in epilepsy and persistent psychiatric side effects following discontinuation

We report a case of a patient with drug-resistant epilepsy treated with deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS). The patient developed psychiatric side effects (PSEs), namely irritability, hostility, aggressiveness, and paranoia, after implantation and stimulation initiation. The stimulation was discontinued and the PSEs were mitigated, but the patient did not return to her pre-implantation state, as documented by repeated psychiatric reports and hospitalizations. To our knowledge, this is the first report of a patient who developed long-term PSEs that did not disappear after stimulation discontinuation. We suppose that ANT-DBS caused a persistent perturbation of the thalamic neuronal networks that are responsible for long-term PSEs.

Open-loop deep brain stimulation for the treatment of epilepsy: a systematic review of clinical outcomes over the past decade (2008-present)

OBJECTIVE The field of deep brain stimulation (DBS) for epilepsy has grown tremendously since its inception in the 1970s and 1980s. The goal of this review is to identify and evaluate all studies published on the topic of open-loop DBS for epilepsy over the past decade (2008 to present). METHODS A PubMed search was conducted to identify all articles reporting clinical outcomes of open-loop DBS for the treatment of epilepsy published since January 1, 2008. The following composite search terms were used: ("epilepsy" [MeSH] OR "seizures" [MeSH] OR "kindling, neurologic" [MeSH] OR epilep* OR seizure* OR convuls*) AND ("deep brain stimulation" [MeSH] OR "deep brain stimulation" OR "DBS") OR ("electric stimulation therapy" [MeSH] OR "electric stimulation therapy" OR "implantable neurostimulators" [MeSH]). RESULTS The authors identified 41 studies that met the criteria for inclusion. The anterior nucleus of the thalamus, centromedian nucleus of the thalamus, and hippocampus were the most frequently evaluated targets. Among the 41 articles, 19 reported on stimulation of the anterior nucleus of the thalamus, 6 evaluated stimulation of the centromedian nucleus of the thalamus, and 9 evaluated stimulation of the hippocampus. The remaining 7 articles reported on the evaluation of alternative DBS targets, including the posterior hypothalamus, subthalamic nucleus, ventral intermediate nucleus of the thalamus, nucleus accumbens, caudal zone incerta, mammillothalamic tract, and fornix. The authors evaluated each study for overall epilepsy response rates as well as adverse events and other significant, nonepilepsy outcomes. CONCLUSIONS Level I evidence supports the safety and efficacy of stimulating the anterior nucleus of the thalamus and the hippocampus for the treatment of medically refractory epilepsy. Level III and IV evidence supports stimulation of other targets for epilepsy. Ongoing research into the efficacy, adverse effects, and mechanisms of open-loop DBS continues to expand the knowledge supporting the use of these treatment modalities in patients with refractory epilepsy.

Image-based analysis and long-term clinical outcomes of deep brain stimulation for Tourette syndrome: a multisite study

BACKGROUND

Deep brain stimulation (DBS) can be an effective therapy for tics and comorbidities in select cases of severe, treatment-refractory Tourette syndrome (TS). Clinical responses remain variable across patients, which may be attributed to differences in the location of the neuroanatomical regions being stimulated. We evaluated active contact locations and regions of stimulation across a large cohort of patients with TS in an effort to guide future targeting.

METHODS

We collected retrospective clinical data and imaging from 13 international sites on 123 patients. We assessed the effects of DBS over time in 110 patients who were implanted in the centromedial (CM) thalamus (n=51), globus pallidus internus (GPi) (n=47), nucleus accumbens/anterior limb of the internal capsule (n=4) or a combination of targets (n=8). Contact locations (n=70 patients) and volumes of tissue activated (n=63 patients) were coregistered to create probabilistic stimulation atlases.

RESULTS

Tics and obsessive-compulsive behaviour (OCB) significantly improved over time (p<0.01), and there were no significant differences across brain targets (p>0.05). The median time was 13 months to reach a 40% improvement in tics, and there were no significant differences across targets (p=0.84), presence of OCB (p=0.09) or age at implantation (p=0.08). Active contacts were generally clustered near the target nuclei, with some variability that may reflect differences in targeting protocols, lead models and contact configurations. There were regions within and surrounding GPi and CM thalamus that improved tics for some patients but were ineffective for others. Regions within, superior or medial to GPi were associated with a greater improvement in OCB than regions inferior to GPi.

CONCLUSION

The results collectively indicate that DBS may improve tics and OCB, the effects may develop over several months, and stimulation locations relative to structural anatomy alone may not predict response. This study was the first to visualise and evaluate the regions of stimulation across a large cohort of patients with TS to generate new hypotheses about potential targets for improving tics and comorbidities.

Network Basis of Seizures Induced by Deep Brain Stimulation: Literature Review and Connectivity Analysis

BACKGROUND

Whereas transient, self-limiting seizures are an infrequent but known complication of deep brain stimulation (DBS) implantation surgery, stimulation itself has occasionally been reported to result in seizure activity at delayed time points. The neural circuitry implicated in stimulation-induced seizures is unknown.

CASE DESCRIPTION

A 47-year-old woman underwent chronic subcallosal cingulate DBS for treatment of refractory anorexia nervosa and experienced seizure with stimulation onset. Supratherapeutic voltage caused a generalized seizure. The patient subsequently experienced a full recovery. We reviewed the literature for other cases of delayed postoperative DBS seizures associated with stimulation. We also investigated whether the higher voltage may have recruited networks implicated in epilepsy. The supratherapeutic voltage stimulated a larger area and engaged vulnerable networks, including bilateral hippocampi, cingulate gyrus, and temporal lobes. Literature review identified 20 studies reporting delayed seizure after DBS surgery, 13 of which demonstrated a robust association with mostly nonmotor DBS stimulation.

CONCLUSIONS

Nonmotor DBS targets, particularly in patients with epilepsy, may be more vulnerable to stimulation-induced seizures; as such, extra caution should be used when programming stimulation parameters at these DBS targets.

Neuromodulation beyond neurostimulation for epilepsy: scope for focused ultrasound

Introduction: Epilepsy is one of the most common neurological disorders and is often difficult to control with medication. Intractable epilepsy often results in compromised quality of life (QOL), neurologic morbidity and even mortality. In carefully selected cases, resective surgery offers the best potential for cure or seizure control. However, a large proportion of patients are not suitable for resective epilepsy surgery. Neuromodulation techniques are increasingly being used to treat such refractory cases. Recently, the FDA approved Magnetic Resonance-guided Focused Ultrasound (MRgFUS) for essential tremor and this novel technology is also being explored in several other neuropsychiatric conditions and neurological disorders, including epilepsy. Area covered: While the literature is scant and scattered, the pertinent literature of the MRgFUS is reviewed with an emphasis on research relevant to its application for epilepsy. Expert opinion: Limited preliminary clinical experiences and research studies with MRgFUS ablation or neuromodulation for epilepsy have shown promising results; however, this procedure remains experimental requiring further investigations. Safe and reversible opening of the blood-brain barrier (BBB) with MRgFUS adds an additional therapeutic avenue by allowing targeted delivery of neurotherapeutics in neurological disorders, potentially including epilepsy. Ongoing clinical trials and research coupled with technological advancements contribute to strengthening the MRgFUS epilepsy field. MRgFUS could be the future technology of choice for 'ablation' or 'sononeuromodulation', and/or a 'targeted therapeutics' for epilepsy.

Deep Brain Stimulation and Drug-Resistant Epilepsy: A Review of the Literature

Introduction: Deep brain stimulation is a safe and effective neurointerventional technique for the treatment of movement disorders. Electrical stimulation of subcortical structures may exert a control on seizure generators initiating epileptic activities. The aim of this review is to present the targets of the deep brain stimulation for the treatment of drug-resistant epilepsy. Methods: We performed a structured review of the literature from 1980 to 2018 using Medline and PubMed. Articles assessing the impact of deep brain stimulation on seizure frequency in patients with DRE were selected. Meta-analyses, randomized controlled trials, and observational studies were included. Results: To date, deep brain stimulation of various neural targets has been investigated in animal experiments and humans. This article presents the use of stimulation of the anterior and centromedian nucleus of the thalamus, hippocampus, basal ganglia, cerebellum and hypothalamus. Anterior thalamic stimulation has demonstrated efficacy and there is evidence to recommend it as the target of choice. Conclusion: Deep brain stimulation for seizures may be an option in patients with drug-resistant epilepsy. Anterior thalamic nucleus stimulation could be recommended over other targets.

Deep brain stimulation of the anterior nucleus of the thalamus for drug-resistant epilepsy

Despite the use of first-choice anti-epileptic drugs and satisfactory seizure outcome rates after resective epilepsy surgery, a considerable percentage of patients do not become seizure free. ANT-DBS may provide for an alternative treatment option in these patients. This literature review discusses the rationale, mechanism of action, clinical efficacy, safety, and tolerability of ANT-DBS in drug-resistant epilepsy patients. A review using systematic methods of the available literature was performed using relevant databases including Medline, Embase, and the Cochrane Library pertaining to the different aspects ANT-DBS. ANT-DBS for drug-resistant epilepsy is a safe, effective and well-tolerated therapy, where a special emphasis must be given to monitoring and neuropsychological assessment of both depression and memory function. Three patterns of seizure control by ANT-DBS are recognized, of which a delayed stimulation effect may account for an improved long-term response rate. ANT-DBS remotely modulates neuronal network excitability through overriding pathological electrical activity, decrease neuronal cell loss, through immune response inhibition or modulation of neuronal energy metabolism. ANT-DBS is an efficacious treatment modality, even when curative procedures or lesser invasive neuromodulative techniques failed. When compared to VNS, ANT-DBS shows slightly superior treatment response, which urges for direct comparative trials. Based on the available evidence ANT-DBS and VNS therapies are currently both superior compared to non-invasive neuromodulation techniques such as t-VNS and rTMS. Additional in-vivo research is necessary in order to gain more insight into the mechanism of action of ANT-DBS in localization-related epilepsy which will allow for treatment optimization. Randomized clinical studies in search of the optimal target in well-defined epilepsy patient populations, will ultimately allow for optimal patient stratification when applying DBS for drug-resistant patients with epilepsy.

Single-Cell Recordings to Target the Anterior Nucleus of the Thalamus in Deep Brain Stimulation for Patients with Refractory Epilepsy

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is a promising treatment for patients with refractory epilepsy. However, therapy response varies and precise positioning of the DBS lead is potentially essential for maximizing therapeutic efficacy. We investigate if single-cell recordings acquired by microelectrode recordings can aid targeting of the ANT during surgery and hypothesize that the neuronal firing properties of the target region relate to clinical outcome. We prospectively included 10 refractory epilepsy patients and performed microelectrode recordings under general anesthesia to identify the change in neuronal signals when approaching and transecting the ANT. The neuronal firing properties of the target region, anatomical locations of microelectrode recordings and active contact positions of the DBS lead along the recorded trajectory were compared between responders and nonresponders to DBS. We obtained 19 sets of recordings from 10 patients (five responders and five nonresponders). Amongst the 403 neurons detected, 365 (90.6%) were classified as bursty. Entry into the ANT was characterized by an increase in firing rate while exit of the ANT was characterized by a decrease in firing rate. Comparing the trajectories of responders to nonresponders, we found differences neither in the neuronal firing properties themselves nor in their locations relative to the position of the active contact. Single-cell firing rate acquired by microelectrode recordings under general anesthesia can thus aid targeting of the ANT during surgery, but is not related to clinical outcome in DBS for patients with refractory epilepsy.

A systematic review of deep brain stimulation for the treatment of drug-resistant epilepsy in childhood

OBJECTIVE Drug-resistant epilepsy (DRE) presents a therapeutic challenge in children, necessitating the consideration of multiple treatment options. Although deep brain stimulation (DBS) has been studied in adults with DRE, little evidence is available to guide clinicians regarding the application of this potentially valuable tool in children. Here, the authors present the first systematic review aimed at understanding the safety and efficacy of DBS for DRE in pediatric populations, emphasizing patient selection, device placement and programming, and seizure outcomes. METHODS The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and recommendations. Relevant articles were identified from 3 electronic databases (MEDLINE, Embase, and Cochrane CENTRAL) from their inception to November 17, 2017. Inclusion criteria of individual studies were 1) diagnosis of DRE; 2) treatment with DBS; 3) inclusion of at least 1 pediatric patient (age ≤ 18 years); and 4) patient-specific data. Exclusion criteria for the systematic review included 1) missing data for age, DBS target, or seizure freedom; 2) nonhuman subjects; and 3) editorials, abstracts, review articles, and dissertations. RESULTS This review identified 21 studies and 40 unique pediatric patients (ages 4–18 years) who received DBS treatment for epilepsy. There were 18 patients with electrodes placed in the bilateral or unilateral centromedian nucleus of the thalamus (CM) electrodes, 8 patients with bilateral anterior thalamic nucleus (ATN) electrodes, 5 patients with bilateral and unilateral hippocampal electrodes, 3 patients with bilateral subthalamic nucleus (STN) and 1 patient with unilateral STN electrodes, 2 patients with bilateral posteromedial hypothalamus electrodes, 2 patients with unilateral mammillothalamic tract electrodes, and 1 patient with caudal zona incerta electrode placement. Overall, 5 of the 40 (12.5%) patients had an International League Against Epilepsy class I (i.e., seizure-free) outcome, and 34 of the 40 (85%) patients had seizure reduction with DBS stimulation. CONCLUSIONS DBS is an alternative or adjuvant treatment for children with DRE. Prospective registries and future clinical trials are needed to identify the optimal DBS target, although favorable outcomes are reported with both CM and ATN in children. ABBREVIATIONS ATN = anterior thalamic nucleus; CM = centromedian nucleus of the thalamus; DBS = deep brain stimulation; DRE = drug-resistant epilepsy; RNS = responsive neurostimulation; STN = subthalamic nucleus; VNS = vagus nerve stimulation.

Anterior thalamic deep brain stimulation in refractory epilepsy: A randomized, double-blinded study

OBJECTIVES

The safety and effect on seizure frequency of anterior thalamic nucleus deep brain stimulation were studied in this prospective, randomized, double-blinded study. Patients were followed for 12 months. The first 6 months were blinded with regard to active stimulation or not. After 6 months, all patients received active stimulation.

MATERIAL AND METHODS

Bilateral ANT electrodes were implanted into 18 patients suffering from focal, pharmacoresistant epilepsy. Antiepileptic treatment was kept unchanged from three months prior to operation. The Liverpool seizure severity scale (LSSS) was used to measure the burden of epilepsy.

RESULTS

There was no significant difference between the 2 groups at the end of the blinded period at 6 months. However, when considering all patients and comparing 6 months of stimulation with baseline, there was a significant, 22% reduction in the frequency of all seizures (P = 0.009). Four patients had ≥50% reduction in total seizure frequency and 5 patients ≥50% reduction in focal seizures after 6 months of stimulation. No increased effect over time was shown. LSSS at 6 months compared to baseline showed no significant difference between the 2 groups, but a small, significant reduction in LSSS was found when all patients had received stimulation for 6 months.

CONCLUSIONS

Our study supports results from earlier studies concerning DBS as a safe treatment option, with effects even in patients with severe, refractory epilepsy. However, our results are not as encouraging as those reported from many other, mainly unblinded, and open studies.

Potential Deep Brain Stimulation Targets for the Management of Refractory Hypertension

Hypertension is the single greatest contributor to human disease and mortality affecting over 75 million people in the United States alone. Hypertension is defined according to the American College of Cardiology as systolic blood pressure (SBP) greater than 120 mm Hg and diastolic blood pressure (DBP) above 80 mm Hg measured on two separate occasions. While there are multiple medication classes available for blood pressure control, fewer than 50% of hypertensive patients maintain appropriate control. In fact, 0.5% of patients are refractory to medical treatment which is defined as uncontrolled blood pressure despite treatment with five classes of antihypertensive agents. With new guidelines to define hypertension that will increase the incidence of hypertension world-wide, the prevalence of refractory hypertension is expected to increase. Thus, investigation into alternative methods of blood pressure control will be crucial to reduce comorbidities such as higher risk of myocardial infarction, cardiovascular accident, aneurysm formation, heart failure, coronary artery disease, end stage renal disease, arrhythmia, left ventricular hypertrophy, intracerebral hemorrhage, hypertensive enchaphelopathy, hypertensive retinopathy, glomerulosclerosis, limb loss due to arterial occlusion, and sudden death. Recently, studies demonstrated efficacious treatment of neurological diseases with deep brain stimulation (DBS) for Tourette's, depression, intermittent explosive disorder, epilepsy, chronic pain, and headache as these diseases have defined neurophysiology with anatomical targets. Currently, clinical applications of DBS is limited to neurological conditions as such conditions have well-defined neurophysiology and anatomy. However, rapidly expanding knowledge about neuroanatomical controls of systemic conditions such as hypertension are expanding the possibilities for DBS neuromodulation. Within the central autonomic network (CAN), multiple regions play a role in homeostasis and blood pressure control that could be DBS targets. While the best defined autonomic target is the ventrolateral periaqueductal gray matter, other targets including the subcallosal neocortex, subthalamic nucleus (STN), posterior hypothalamus, rostrocaudal cingulate gyrus, orbitofrontal gyrus, and insular cortex are being further characterized as potential targets. This review aims to summarize the current knowledge regarding neurologic contribution to the pathophysiology of hypertension, delineate the complex interactions between neuroanatomic structures involved in blood pressure homeostasis, and then discuss the potential for using DBS as a treatment for refractory hypertension.

Deep Brain Stimulation Works for Drug-Resistant Epilepsy, But How?

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Deep brain stimulation probing performance is enhanced by pairing stimulus with epileptic seizure

The unpredictability of spontaneous and recurrent seizures significantly impairs the quality of life of patients with epilepsy. Probing neural network excitability with deep brain electrical stimulation (DBS) has shown promising results predicting pathological shifts in brain states. This work presents a proof-of-principal that active electroencephalographic (EEG) probing, as a seizure predictive tool, is enhanced by pairing DBS and the electrographic seizure itself. The ictogenic model used consisted of inducing seizures by continuous intravenous infusion of pentylenetetrazol (PTZ - 2.5 mg/ml/min) while a probing DBS was delivered to the thalamus (TH) or amygdaloid complex to detect changes prior to seizure onset. Cortical electrophysiological recordings were performed before, during, and after PTZ infusion. Thalamic DBS probing, but not amygdaloid, was able to predict seizure onset without any observable proconvulsant effects. However, previously pairing amygdaloid DBS and epileptic polyspike discharges (day-1) elicited distinct preictal cortically recorded evoked response (CRER) (day-2) when compared with control groups that received the same amount of electrical pulses at different moments of the ictogenic progress at day-1. In conclusion, our results have demonstrated that the pairing strategy potentiated the detection of an altered brain state prior to the seizure onset. The EEG probing enhancement method opens many possibilities for both diagnosis and treatment of epilepsy.

Deep brain stimulation for epilepsy

The efficacy and safety of deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) for epilepsy (SANTE) trial was demonstrated by a randomized trial by Fisher et al. (2010). Based on this trial, the U.S. Food and Drug Administration recently granted approval for DBS therapy for epilepsy; the indication is as follows: "Bilateral stimulation of the anterior nucleus of the thalamus (ANT) for epilepsy is indicated as an adjunctive therapy for reducing the frequency of seizures in individuals 18 years of age or older diagnosed with epilepsy characterized by partial onset seizures with or without secondary generalization that are refractory to three or more antiepileptic medications". This paper reviews the experimental data and the clinical experience using DBS for the treatment of epilepsy. "This article is part of the Supplement issue Neurostimulation for Epilepsy."

Understanding Deep Brain Stimulation: In Vivo Metabolic Consequences of the Electrode Insertional Effect

Deep brain stimulation (DBS) is a neurosurgery technique widely used in movement disorders, although its mechanism of action remains unclear. In fact, apart from the stimulation itself, the mechanical insertion of the electrode may play a crucial role. Here we aimed to distinguish between the insertional and the DBS effects on brain glucose metabolism. To this end, electrodes were implanted targeting the medial prefrontal cortex in five adult male Wistar rats. Positron Emission Tomography (PET) studies were performed before surgery (D0) and seven (D7) and nine days (D9) after that. DBS was applied during the 18FDG uptake of the D9 study. PET data were analysed with statistical parametric mapping. We found an electrode insertional effect in cortical areas, while DBS resulted in a more widespread metabolic pattern. The consequences of simultaneous electrode and DBS factors revealed a combination of both effects. Therefore, the insertion metabolic effects differed from the stimulation ones, which should be considered when assessing DBS protocols.

Electrical Stimulation of the Anterior Thalamus for Epilepsy: Clinical Outcome and Analysis of Efficient Target

OBJECTIVE

Deep brain stimulation (DBS) of the anterior thalamic complex (ANT) is an adjunctive therapy for pharmacoresistant epilepsy. To define the most efficient target in DBS for epilepsy, we investigate clinical data, position of leads, usability of atlas data compared to electric field modeling based on programming parameters.

METHODS

Data from ten consecutive patients who underwent ANT-DBS were analyzed. The mammillothalamic tract (MTT), an internal landmark for direct stereotactic targeting, was segmented from MRI. Centers of stimulation were determined and their positions relative to ventricles and the MTT were analyzed. Two 3D thalamus atlases were transformed to segmented patient's thalami and proportions of activated nuclei were calculated.

RESULTS

Our data indicate higher response rates with a center of stimulation 5 mm lateral to the wall of the third ventricle (R² for reduction of focal seizure frequency and distance to the wall of the third ventricle = 0.48, p = 0.026). For reduction of focal seizures, a strong positive correlation with the dorsal distance to the midcommissural plane was found (R² = 0.66, p = 0.004). In one 3D atlas, stimulation of internal medullary lamina (IML) correlated strongly positive with response rates, which, however, did not reach statistical significance (R² = 0.69, p = 0.17 for tonic-clonic seizures). All electrical fields covered the diameter of the MTT. The position of the MTT in the thalamus was highly variable (range: x-coordinate 4.0 to 7.3 mm, y-coordinate -1.3 to 5.1 mm in AC-PC space).

CONCLUSIONS

The distance of the active contact to the lateral wall of the third ventricle, MTT and the ventrodorsal distance to midcommissural plane appear to be relevant for optimal target planning. For reduction of focal seizure frequency, we found best response rates with a center of stimulation 5 mm lateral to the wall of the third ventricle, and a lead tip 10 mm dorsal of the midcommissural plane.

Fast gray matter acquisition T1 inversion recovery MRI to delineate the mammillothalamic tract for preoperative direct targeting of the anterior nucleus of the thalamus for deep brain stimulation in epilepsy

When medically intractable epilepsy is multifocal or focal but poorly localized, neuromodulation can be useful therapy. One such technique is deep brain stimulation (DBS) targeting the anterior nucleus of the thalamus (ANT). Unfortunately, the ANT is difficult to visualize in standard MRI sequences and its indirect targeting is difficult because of thalamic variability and atrophy in patients with epilepsy. The following study describes the novel use of the fast gray matter acquisition T1 inversion recovery (FGATIR) MRI sequence to delineate the mammillothalamic tract for direct targeting of the ANT through visualizing the termination of the mammillothalamic tract in the ANT.

The day prior to surgery in a 19-year-old, right-handed woman with a 5-year history of epilepsy, MRI was performed on a 3-T Siemens Prisma scanner (Siemens AG, Healthcare Sector) using a 64-channel head and neck coil. As part of the imaging protocol, noncontrast magnetization-prepared rapid gradient echo (MP-RAGE) and diffusion tensor imaging (DTI) sequences were obtained for targeting purposes. The ANT was directly targeted using the FGATIR sequence, and bilateral Medtronic 3389 leads were placed. At the last follow-up (2 months), the patient reported an approximate 75% decrease in seizure frequency, as well as a decrease in seizure severity.

Bilateral stereotactic lesions and chronic stimulation of the anterior thalamic nuclei for treatment of pharmacoresistant epilepsy

Background:

The use of the anterior nucleus of thalamus (ANT) as a target for treatment of pharmacoresistant epilepsy is based on its crucial role in seizure propagation. We describe results of chronic bilateral ANT stimulation and bilateral ANT lesions in 31 patients with refractory epilepsy.

Methods:

ANT DBS was performed in 12 patients (group I) and bilateral stereotactic radiofrequency lesions of ANT were performed in 19 patients (group II). Targeting was based on stereotactic atlas information with correction of the final coordinates according to the location of anatomical landmarks and intraoperative microelectrode recording data.

Results:

Both groups were similar in age, gender, seizures frequency, and duration of disease. The median x, y, and z coordinates of ANT were found to be 2.9, 5, and 11 mm anterior, lateral, and superior to the mid-commissural point, respectively. Mean seizures reduction reached 80.3% in group of patients with ANT DBS with two nonresponders and 91.2% in group of patients with lesions. Five patients from group I and three patients from group II became seizure-free. The morbidity rate was low in both groups.

Conclusions:

Stereotactic anterior thalamotomy and chronic ANT stimulation are both effective for seizure control in epilepsy originated from frontal and temporal lobes. ANT lesions and stimulation were more effective for secondary-generalized seizures compared to simple partial seizures.

Technical Implications in Revision Surgery for Deep Brain Stimulation (DBS) of the Thalamus for Refractory Epilepsy

Background and Purpose

Implantation of deep brain stimulation (DBS) electrodes in the anterior nucleus of the thalamus (ANT) or the centromedian nucleus (CM), for the treatment of refractory epilepsy, is technically demanding. To enhance the accuracy of electrode placement within the ANT and CM, we analyzed our experience with electrode revision surgery in ANT and CM DBS and investigated the cause of misplacement and verifying methods for accurate placement.

Methods

A retrospective analysis of the medical records of 23 patients who underwent DBS for refractory epilepsy during the period from 2013 to 2016 was performed.

Results

Misplacement of the electrode occurred in 1 (25%) of 4 ANT DBS and 2 (14.3%) of 14 patients with CM DBS performed in our institute, and revision surgery was performed in three patients. During this period, we performed three revision surgeries for misplaced electrodes in ANT DBS that were performed at another hospital. Therefore, we performed six revision surgeries (four in ANT, two in CM) for mistargeted DBS electrodes for thalamic DBS. Transventricular lead placement and an anatomical targeting of the ANT was the cause of misplacement in the ANT and intraoperative brain shift was found to be the cause in the CM. For verification of the location of lead placement, magnetic resonance imaging (MRI) was superior to computed tomography and electroencephalography (EEG).

Conclusions

To reduce the rate of electrode misplacement for refractory epilepsy, image-based targeting of the ANT according to individual anatomical variation, and efforts to minimize intraoperative brain shift are essential. To verify the location of the electrode, MRI examination is mandatory in DBS for refractory epilepsy.

The generation mechanism of spike-and-slow wave discharges appearing on thalamic relay nuclei

In this paper, we use a model modified from classic corticothalamic network(CT) to explore the mechanism of absence seizures appearing on specific relay nuclei (SRN) of the thalamus. It is found that typical seizure states appear on SRN through tuning several critical connection strengths in the model. In view of previous experimental and theoretical works which were mainly on epilepsy seizure phenomena appearing on excitatory pyramidal neurons (EPN) of the cortex, this is a novel model to consider the seizure observed on thalamus. In particular, the onset mechanism is different from previous theoretical studies. Inspired by some previous clinical and experimental studies, we employ the external stimuli voltage on EPN and SRN in the network, and observe that the seizure can be well inhibited by tuning the stimulus intensity appropriately. We further explore the effect of the signal transmission delays on seizures, and found that the polyspike phenomenon appears only when the delay is sufficiently large. The experimental data also confirmed our model. Since there is a complex network in the brain and all organizations are interacting closely with each other, the results obtained in this paper provide not only biological insights into the regulatory mechanisms but also a reference for the prevention and treatment of epilepsy in future.

Stimulation Induced Electrographic Seizures in Deep Brain Stimulation of the Anterior Nucleus of the Thalamus Do Not Preclude a Subsequent Favorable Treatment Response

Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) is a method of neuromodulation used for refractory focal epilepsy. We report a patient suffering from drug-resistant epilepsy who developed novel visual symptoms and atypical seizures with the onset of ANT-DBS therapy. Rechallenge under video electroencephalography recording confirmed that lowering the stimulation voltage alleviated these symptoms. Subsequent stimulation with the initial voltage value did not cause the recurrence of either the visual symptoms or the new seizure type, and appeared to alleviate the patient's seizures in long-term follow-up. We therefore hypothesize that the occurrence of stimulation induced seizures at the onset of DBS therapy should not be considered as a failure in the DBS therapy, and the possibility of a subsequent favorable response to the treatment still exists.

Deep brain stimulation for drug-resistant epilepsy

OBJECTIVES

To review clinical evidence on the antiepileptic effects of deep brain stimulation (DBS) for drug-resistant epilepsy, its safety, and the factors influencing individual outcomes.

METHODS

A comprehensive search of the medical literature (PubMed, Medline) was conducted to identify relevant articles investigating DBS therapy for drug-resistant epilepsy. Reference lists of these articles were used to source further articles.

RESULTS

Stimulation of the anterior nucleus of the thalamus (ANT) and hippocampus (HC) has been shown to decrease the frequency of refractory seizures. Half of all patients from clinical studies experienced a 46%-90% seizure reduction with ANT-DBS, and a 48%-95% seizure reduction with HC-DBS. The efficacy of stimulating other targets remains inconclusive due to lack of evidence. Approximately three-fourths of patients receiving ANT, HC, or centromedian nucleus of the thalamus (CMT) stimulation are responders-experiencing a seizure reduction of at least 50%. The time course of clinical benefit varies dramatically, with both an initial lesional effect and ongoing stimulation effect at play. Improved quality of life and changes to cognition or mood may also occur. Side effects are similar in nature to those reported from DBS therapy for movement disorders. Several factors are potentially associated with stimulation efficacy, including an absence of structural abnormality on imaging for ANT and HC stimulation, and electrode position relative to the target. Certain seizure types or syndromes may respond more favorably to specific targets, including ANT stimulation for deep temporal or limbic seizures, and CMT stimulation for generalized seizures and Lennox-Gastaut syndrome.

SIGNIFICANCE

We have identified several patient, disease, and stimulation factors that potentially predict seizure outcome following DBS. More large-scale clinical trials are needed to explore different stimulation parameters, reevaluate the indications for DBS, and identify robust predictors of patient response.

Mammillothalamic and Mammillotegmental Tracts as New Targets for Dementia and Epilepsy Treatment

BACKGROUND

Recently, neuromodulation through deep brain stimulation (DBS) has appeared as a new surgical procedure in the treatment of some types of dementia and epilepsy. The mammillothalamic and mammillotegmental tracts are involved among the new targets. To our knowledge, a review article focused specifically on these mammillary body efferents is lacking in the medical literature. Their contribution to memory is, regrettably, often overlooked.

METHODS

A review of the relevant literature was conducted.

RESULTS

There is evidence that mammillary bodies can contribute to memory independently from hippocampal formation, but the mechanism is not yet known. Recent studies in animals have provided evidence for the specific roles of these mammillary body efferents in regulating memory independently. In animal studies, it has been shown that the disruption of the mammillothalamic tract inhibits seizures and that electrical stimulation of the mammillary body or mammillothalamic tract raises the seizure threshold. In humans, DBS targeting the mammillary body through the mammillothalamic tract or the stimulation of the anterior thalamic nucleus, especially in the areas closely related to the mammillothalamic tract, has been found effective in patients with medically refractory epilepsy. Nonetheless, little knowledge exists on the functional anatomy of the mammillary body efferents, and their role in the exact mechanism of epileptogenic activity and in the memory function of the human brain.

CONCLUSIONS

A comprehensive knowledge of the white matter anatomy of the mammillothalamic and mammillotegmental tracts is crucial since they have emerged as new DBS targets in the treatment of various disorders including dementia and epilepsy.

Controlling mechanism of absence seizures by deep brain stimulus applied on subthalamic nucleus

Based on a classical model of the basal ganglia thalamocortical network, in this paper, we employed a type of the deep brain stimulus voltage on the subthalamic nucleus to study the control mechanism of absence epilepsy seizures. We found that the seizure can be well controlled by turning the period and the duration of current stimulation into suitable ranges. It is the very interesting bidirectional periodic adjustment phenomenon. These parameters are easily regulated in clinical practice, therefore, the results obtained in this paper may further help us to understand the treatment mechanism of the epilepsy seizure.

Neurostimulation as a promising epilepsy therapy

The revolution in theory, swift technological developments, and invention of new devices have driven tremendous progress in neurostimulation as a third‐line treatment for epilepsy. Over the past decades, neurostimulation took its place in the field of epilepsy as an advanced treatment technique and opened up a new world. Numerous animal studies have proven the physical efficacy of stimulation of the brain and peripheral nerves. Based on this optimistic fundamental research, new advanced techniques are being explored in clinical practice. Over the past century, drawing on the benefits brought about by vagus nerve stimulation for the treatment of epilepsy, various new neurostimulation modalities have been developed to control seizures. Clinical studies including case reports, case series, and clinical trials have been booming in the past several years. This article gives a comprehensive review of most of these clinical studies. In addition to highlighting the advantages of neurostimulation for the treatment of epilepsy, concerns with this modality and future development directions are also discussed. The biggest advantage of neurostimulation over pharmacological treatments for epilepsy is the modulation of the epilepsy network by delivering stimuli at a specific target or the “hub.” Conversely, however, a lack of knowledge of epilepsy networks and the mechanisms of neurostimulation may hinder further development. Therefore, theoretical research on the mechanism of epileptogenesis and epilepsy networks is needed in the future. Within the multiple modalities of neuromodulation, the final choice should be made after full discussion with a multidisciplinary team at a presurgical conference. Furthermore, the establishment of a neurostimulation system with standardized parameters and rigorous guidelines is another important issue. To achieve this goal, a worldwide collaboration of epilepsy centers is also suggested in the future.

Secondary generalization of focal-onset seizures: examining the relationship between seizure propagation and epilepsy surgery outcome

Surgical intervention often fails to achieve seizure-free results in patients with intractable epilepsy. Identifying features of the epileptic brain that dispose certain patients to unfavorable outcomes is critical for improving surgical candidacy assessments. Recent research by Martinet, Ahmad, Lepage, Cash, and Kramer (J Neurosci 35: 9477-9490, 2015) suggests that pathways of secondary seizure generalization distinguish patients with favorable (i.e., seizure free) vs. unfavorable (i.e., seizure persistent) surgical outcomes, lending insights into the network mechanisms of epilepsy surgery failure.

Assessment of Age-Related Morphometric Changes of Subcortical Structures in Healthy People Using Ultra-High Field 7 Tesla Magnetic Resonance Imaging

Objective: To assess the age-related morphometric changes of subcortical structures in healthy people.

Materials and Methods: Ultra-high field 7 tesla magnetic resonance (MR) imaging in humans was used to visualize the subcortical structures of healthy young, middle-aged and elderly participants. Using the magnetization-prepared two rapid acquisition gradient echo (MP2RAGE) sequence, we assessed the visibility of the margins of the thalamus and white matter in the thalamus, as well as the anterior commissure (AC) and posterior commissure (PC) length, the maximal height of the thalamus, the half width of the third ventricle and the distance between the AC and the center of the mammillothalamic tract (MTT) at the level of the AC-PC plane. All quantitative data were statistically evaluated.

Results: The AC-PC length did not differ significantly among the three groups. The maximal height of the thalamus decreased with age (r_s(53) = −0.719, p < 0.001). The half width of the third ventricle (r_s(53) = 0.705, p < 0.001) and the distance between the AC and the center of the MTT (r_s(53) = 0.485, p < 0.001) increased with age. The distance between the AC and the center of the MTT of the young and the elderly participants differed significantly (p = 0.007).

Conclusion: The AC-PC length is not a good candidate for proportional correction during atlas-to-patient registration. The maximal height of the thalamus and the half width of the third ventricle correlated strongly with age, and the MTT position in relation to the AC shifted posteriorly as age increased. These age-related morphometric changes of subcortical structures should be considered in targeting for functional neurosurgery.

Current and Emerging Surgical Therapies for Severe Pediatric Epilepsies

The use of epilepsy surgery in various medically resistant epilepsies is well established. For patients with intractable pediatric epilepsy, the role of intracranial electrodes, resective surgery, hemispherectomy, corpus callosotomy, neurostimulation, and multiple subpial transections continues to be very effective in select cases. Newer treatment and diagnostic methods include laser thermal ablation, minimally invasive surgeries, stereo electroencephalography, electrocorticography, and other emerging techniques. This article will review the established and emerging surgical therapies for severe pediatric epilepsies, their respective indications and overall efficacy.