"Laser and the Tuber": thermal dynamic and volumetric factors influencing seizure outcomes in pediatric subjects with tuberous sclerosis undergoing stereoencephalography-directed laser ablation of tubers

Pediatric Neurostimulation and Practice Evolution

Since the late nineteenth century, the prevailing view of epilepsy surgery has been to identify a seizure focus in a medically refractory patient and eradicate it. Sadly, only a select number of the many who suffer from uncontrolled seizures benefit from this approach. With the development of safe, efficient stereotactic methods and targeted surgical therapies that can affect deep structures and modulate broad networks in diverse disorders, epilepsy surgery in children has undergone a paradigmatic evolutionary change. With modern diagnostic techniques such as stereo electroencephalography combined with closed loop neuromodulatory systems, pediatric epilepsy surgery can reach a much broader population of underserved patients.

Updated clinical recommendations for the management of tuberous sclerosis complex associated epilepsy

Children with tuberous sclerosis complex (TSC), may experience a variety of seizure types in the first year of life, most often focal seizure sand epileptic spasms. Drug resistance is seen early in many patients, and the management of TSC associated epilepsy remain a major challenge for clinicians. In 2018 clinical recommendations for the management of TSC associated epilepsy were published by a panel of European experts. In the last five years considerable progress has been made in understanding the neurobiology of epileptogenesis and three interventional randomized controlled trials have changed the therapeutic approach for the management of TSC associated epilepsy. Pre-symptomatic treatment with vigabatrin may delay seizure onset, may reduce seizure severity and reduce the risk of epileptic encephalopathy. The efficacy of mTOR inhibition with adjunctive everolimus was documented in patients with TSC associated refractory seizures and cannabidiol could be another therapeutic option. Epilepsy surgery has significantly improved seizure outcome in selected patients and should be considered early in all patients with drug resistant epilepsy. There is a need to identify patients who may have a higher risk of developing epilepsy and autism spectrum disorder (ASD). In the recent years significant progress has been made owing to the early identification of risk factors for the development of drug-resistant epilepsy. Better understanding of the mechanism underlying epileptogenesis may improve the management for TSC-related epilepsy. Developmental neurobiology and neuropathology give opportunities for the implementation of concepts related to clinical findings, and an early genetic diagnosis and use of EEG and MRI biomarkers may improve the development of pre-symptomatic and disease-modifying strategies.

Paradigm shift in the treatment of tuberous sclerosis: Effectiveness of everolimus

Tuberous sclerosis complex (TSC) is an autosomal dominant disease characterised by abnormal cell proliferation and differentiation that affects multiple organs and can lead to the growth of hamartomas. Tuberous sclerosis complex is caused by the disinhibition of the protein mTOR (mammalian target of rapamycin). In the past, various therapeutic approaches, even if only symptomatic, have been attempted to improve the clinical effects of this disease. While all of these therapeutic strategies are useful and are still used and indicated, they are symptomatic therapies based on the individual symptoms of the disease and therefore not fully effective in modifying long-term outcomes. A new therapeutic approach is the introduction of allosteric inhibitors of mTORC1, which allow restoration of metabolic homeostasis in mutant cells, potentially eliminating most of the clinical manifestations associated with Tuberous sclerosis complex. Everolimus, a mammalian target of the rapamycin inhibitor, is able to reduce hamartomas, correcting the specific molecular defect that causes Tuberous sclerosis complex. In this review, we report the findings from the literature on the use of everolimus as an effective and safe drug in the treatment of TSC manifestations affecting various organs, from the central nervous system to the heart.

Epilepsy Surgery in Young Children With Tuberous Sclerosis Complex: A Novel Hybrid Multimodal Surgical Approach

BACKGROUND

Surgery has become integral in treating children with tuberous sclerosis complex (TSC)-related drug-resistant epilepsy (DRE).

OBJECTIVE

To describe outcomes of a multimodal diagnostic and therapeutic approach comprising invasive intracranial monitoring and surgical treatment and compare the complementary techniques of open resection and magnetic resonance-guided laser interstitial thermal therapy.

METHODS

Clinical and radiographic data were prospectively collected for pediatric patients undergoing surgical evaluation for TSC-related DRE at our tertiary academic hospital. Seizure freedom, developmental improvement, and Engel class were compared.

RESULTS

Thirty-eight patients (20 females) underwent treatment in January 2016 to April 2019. Thirty-five underwent phase II invasive monitoring with intracranial electrodes: 24 stereoencephalography, 9 craniotomy for grid/electrode placement, and 2 grids + stereoencephalography. With the multimodal approach, 33/38 patients (87%) achieved >50% seizure freedom of the targeted seizure type after initial treatment; 6/9 requiring secondary treatment and 2/2 requiring a third treatment achieved >50% freedom. The median Engel class was II at last follow-up (1.65 years), and 55% of patients were Engel class I/II. The mean age was lower for children undergoing open resection (2.4 vs 4.9 years, P = .04). Rates of >50% reduction in seizures (86% open resection vs 88% laser interstitial thermal therapy) and developmental improvement (86% open resection vs 83% magnetic resonance-guided laser interstitial thermal therapy) were similar.

CONCLUSION

This hybrid approach of using both open surgical and minimally invasive techniques is safe and effective in treating DRE secondary to TSC. Clinical trials focused on treatment method with longer follow-up are needed to determine the optimal candidates for each approach and compare the treatment modalities more effectively.

Progress of clinical research studies on tuberous sclerosis complex-related epilepsy in China

Tuberous sclerosis complex (TSC) is an autosomal dominant neurocutaneous syndrome, with 75.6%-83.5% and 54.1% patients presenting with epilepsy and drug-resistant epilepsy (DRE), respectively. Clinical studies on TSC, particularly surgical interventions, have achieved rapid and substantial progress. The TSC-Task Force Committee of the China Association Against Epilepsy (CAAE-TFTSC) was founded in 2012, and annual academic conferences on the surgical treatment of TSC-related epilepsy have been held since 2013. 'China experts' consensus on surgical treatment of TSC-related epilepsy' was published in 2019. This review focuses on surgical treatment, including resective surgery, neuromodulations, corpus callosotomy and mini-invasive ablations, as well as studies on phenotype, genotype and anti-seizure therapies of mammalian target of rapamycin inhibitor, vigabatrin and ketogenic diet in patients with TSC-related DRE in China.

Current role of surgery for tuberous sclerosis complex‐associated epilepsy

Tuberous sclerosis complex (TSC) is a rare multisystem, autosomal dominant neurocutaneous syndrome in which epilepsy is the most common of several neurological and psychiatric manifestations. Around two thirds of patients develop drug‐resistant epilepsy for whom surgical resection of epileptogenic foci is indicated when seizures remain inadequately controlled following trial of two antiseizure medications. The challenge with presurgical and surgical approaches with patients with TSC is overcoming the complexity from the number of tubers and the multiplex epileptogenic network forming the epileptogenic zone. Data suggest that seizure freedom is achieved by 55%–60% of patients, but predictive factors for success have remained elusive, which makes for unconfident selection of surgical candidates. This article presents three different cases as illustrations of the potential challenges faced when assessing the suitability of TSC patients for epilepsy surgery.

Global and intertuberal epileptic networks in tuberous sclerosis based on stereoelectroencephalographic (sEEG) findings: a quantitative EEG analysis in pediatric subjects and surgical implications

OBJECTIVE

Recent evidence favors a network concept in tuberous sclerosis (TSC) with seizure generation and propagation related to changes in global and regional connectivity between multiple, anatomically distant tubers. Direct exploration of network dynamics in TSC has been made possible through intracranial sampling with stereoelectroencephalography (sEEG). The objective of this study is to define epileptic networks in TSC using quantitative analysis of sEEG recordings. We also discuss the impact of the definition of these epileptic networks on surgical decision-making.

METHODS

Intracranial sEEG recordings were obtained from four pediatric patients who presented with medically refractory epilepsy secondary to TSC and subjected to quantitative signal analysis methods. Cortical connectivity was quantified by calculating pairwise coherence between all contacts and constructing an association matrix. The global coherence, defined as the ratio of the largest eigenvalue to the sum of all the eigenvalues, was calculated for each frequency band (delta, theta, alpha, beta, gamma). Spatial distribution of the connectivity was identified by plotting the leading principal component (product of the largest eigenvalue and its corresponding eigenvector).

RESULTS

Four pediatric subjects with TSC underwent invasive intracranial monitoring with sEEG, comprising 31 depth electrodes and 250 contacts, for localization of the epileptogenic focus and guidance of subsequent surgical intervention. Quantitative connectivity analysis revealed a change in global coherence during the ictal period in the beta/low gamma (14-30 Hz) and high gamma (31-80 Hz) bands. Our results corroborate findings from existing literature, which implicate higher frequencies as a driver of synchrony and desynchrony.

CONCLUSIONS

Coordinated high-frequency activity in the beta/low gamma and high gamma bands among spatially distant sEEG define the ictal period in TSC. This time-dependent change in global coherence demonstrates evidence for intra-tuberal and inter-tuberal connectivity in TSC. This observation has surgical implications. It suggests that targeting multiple tubers has a higher chance of seizure control as there is a higher chance of disrupting the epileptic network. The use of laser interstitial thermal therapy (LITT) allowed us to target multiple disparately located tubers in a minimally invasive manner with good seizure control outcomes.

Three Dimensional Brain Reconstruction Optimizes Surgical Approaches and Medical Education in Minimally Invasive Neurosurgery for Refractory Epilepsy

Epilepsy is a prevalent condition that affects 1–3% of the population or about 50–65 million people worldwide (WHO estimates) and about 3.5 million people in the USA alone (CDC estimates). Refractory epilepsy refers to patients that respond inadequately to medical management alone (at least two anti-seizure medications at appropriate doses) and are appropriate candidates for other interventions such as brain surgery or the use of neurostimulators for their epilepsy. Minimally invasive techniques like stereotactic EEG electrodes offer excellent investigational abilities to study the diagnostic attributes of the seizure networks, while therapies like laser ablations and neurostimulators permit intervention and modulation of these networks to offer seizure control with minimal cognitive compromise and surgical morbidity. The accuracy of these techniques is highly contingent on precise anatomical correlation between the location of the electrodes and their proximity to relevant structures of the brain. Ensuring good anatomical correlation using 3-dimensional (3D) reconstructions would permit precise localization and accurate understanding of the seizure networks. Accurate localization of stereotactic electrodes would enable precise understanding of the electrical networks and identify vital nodes in the seizure network. These reconstructions would also permit better understanding of the proximity of these electrodes to each other and help confirm arrangement of neurostimulators to maximize modulatory effects on the networks. Such reconstructions would enable better understanding of neuroanatomy and connectivity to improve knowledge of brain structures and relations in neurological conditions. These methods would enable medical students and doctors-in-training to better their understanding of neurological disease and the necessary interventions.

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.

Review of the treatment options for epilepsy in tuberous sclerosis complex: towards precision medicine

Tuberous sclerosis complex (TSC) is a rare genetic disorder caused by mutations in the TSC1 or TSC2 genes, which encode proteins that antagonise the mammalian isoform of the target of rapamycin complex 1 (mTORC1) - a key mediator of cell growth and metabolism. TSC is characterised by the development of benign tumours in multiple organs, together with neurological manifestations including epilepsy and TSC-associated neuropsychiatric disorders (TAND). Epilepsy occurs frequently and is associated with significant morbidity and mortality; however, the management is challenging due to the intractable nature of the seizures. Preventative epilepsy treatment is a key aim, especially as patients with epilepsy may be at a higher risk of developing severe cognitive and behavioural impairment. Vigabatrin given preventatively reduces the risk and severity of epilepsy although the benefits for TAND are inconclusive. These promising results could pave the way for evaluating other treatments in a preventative capacity, especially those that may address the underlying pathophysiology of TSC, including everolimus, cannabidiol and the ketogenic diet (KD). Everolimus is an mTOR inhibitor approved for the adjunctive treatment of refractory TSC-associated seizures that has demonstrated significant reductions in seizure frequency compared with placebo, improvements that were sustained after 2 years of treatment. Highly purified cannabidiol, recently approved in the US as Epidiolex® for TSC-associated seizures in patients ⩾1 years of age, and the KD, may also participate in the regulation of the mTOR pathway. This review focusses on the pivotal clinical evidence surrounding these potential targeted therapies that may form the foundation of precision medicine for TSC-associated epilepsy, as well as other current treatments including anti-seizure drugs, vagus nerve stimulation and surgery. New future therapies are also discussed, together with the potential for preventative treatment with targeted therapies. Due to advances in understanding the molecular genetics and pathophysiology, TSC represents a prototypic clinical syndrome for studying epileptogenesis and the impact of precision medicine.

Current applications and safety profile of laser interstitial thermal therapy in the pediatric population: a systematic review of the literature

OBJECTIVE

Laser interstitial thermal therapy (LITT) provides a minimally invasive alternative to open brain surgery, making it a powerful neurosurgical tool especially in pediatric patients. This systematic review aimed to highlight the indications and complications of LITT in the pediatric population.

METHODS

In line with the PRISMA guidelines, the authors conducted a systematic review to summarize the current applications and safety profiles of LITT in pediatrics. PubMed and Embase were searched for studies that reported the outcomes of LITT in patients < 21 years of age. Retrospective studies, case series, and case reports were included. Two authors independently screened the articles by title and abstract followed by full text. Relevant variables were extracted from studies that met final eligibility, and results were pooled using descriptive statistics.

RESULTS

The selection process captured 303 pediatric LITT procedures across 35 studies. Males comprised approximately 60% of the aggregate sample, with a mean age of 10.5 years (range 0.5-21 years). The LITT technologies used included Visualase (89%), NeuroBlate (9%), and Multilase 2100 (2%). The most common indication was treatment of seizures (86%), followed by brain tumors (16%). The mean follow-up duration was 15.6 months (range 1.3-48 months). The overall complication rate was 15.8%, which comprised transient neurological deficits, cognitive and electrolyte disturbances, hemorrhage, edema, and hydrocephalus. No deaths were reported.

CONCLUSIONS

As of now, LITT's most common applications in pediatrics are focused on treating medically refractory epilepsy and brain tumors that can be difficult to resect. The safety of LITT can provide an attractive alternative to open brain surgery in the pediatric population.

Epilepsy Surgery: Monitoring and Novel Surgical Techniques

Drug-resistant epilepsy warrants referral to an epilepsy surgery center for consideration of alternative treatments including epilepsy surgery. Advances in technology now allow for minimally invasive neurophysiologic monitoring and surgical interventions, approaches that are attractive to families because large craniotomies and associated morbidity are avoided. This work reviews the presurgical evaluation process and discusses the use of invasive stereo-electroencephalography monitoring to localize seizure onset zones. Minimally invasive surgical techniques are described for the treatment of focal and generalized epilepsies. These approaches have expanded our capacity to palliate and cure epilepsy in the pediatric population.

Epilepsy surgery in tuberous sclerosis complex (TSC): emerging techniques and redefinition of treatment goals

Epilepsy occurs in nearly all patients with tuberous sclerosis and is often refractory to medical treatment. The definition of surgical candidacy in these patients has broadened in recent years due to philosophical and technological advances. The goals of surgery have shifted to focusing on quality of life and maximizing neurodevelopmental potential in patients unable to obtain seizure freedom. Novel diagnostic, ablative, and neuromodulatory techniques have been developed that may help patients that were previously considered inoperable to have an improved quality of life. In the coming years, it is expected that these techniques will be further refined and lead to an improvement of neurological prognosis in patients with tuberous sclerosis.

Postoperative outcomes following pediatric intracranial electrode monitoring: A case for stereoelectroencephalography (SEEG)

BACKGROUND

For patients with medically refractory epilepsy, intracranial electrode monitoring can help identify epileptogenic foci. Despite the increasing utilization of stereoelectroencephalography (SEEG), the relative risks or benefits associated with the technique when compared with the traditional subdural electrode monitoring (SDE) remain unclear, especially in the pediatric population. Our aim was to compare the outcomes of pediatric patients who received intracranial monitoring with SEEG or SDE (grids and strips).

METHODS

We retrospectively studied 38 consecutive pediatric intracranial electrode monitoring cases performed at our institution from 2014 to 2017. Medical/surgical history and operative/postoperative records were reviewed. We also compared direct inpatient hospital costs associated with the two procedures.

RESULTS

Stereoelectroencephalography and SDE cohorts both showed high likelihood of identifying epileptogenic zones (SEEG: 90.9%, SDE: 87.5%). Compared with SDE, SEEG patients had a significantly shorter operative time (118.7 versus 233.4 min, P < .001) and length of stay (6.2 versus 12.3 days, P < .001), including days spent in the intensive care unit (ICU; 1.4 versus 5.4 days, P < .001). Stereoelectroencephalography patients tended to report lower pain scores and used significantly less narcotic pain medications (54.2 versus 197.3 mg morphine equivalents, P = .005). No complications were observed. Stereoelectroencephalography and SDE cohorts had comparable inpatient hospital costs (P = .47).

CONCLUSION

In comparison with subdural electrode placement, SEEG results in a similarly favorable clinical outcome, but with reduced operative time, decreased narcotic usage, and superior pain control without requiring significantly higher costs. The potential for an improved postoperative intracranial electrode monitoring experience makes SEEG especially suitable for pediatric patients.

Magnetic Resonance-Guided Laser Interstitial Thermal Therapy for the Treatment of Nonlesional Insular Epilepsy in Pediatric Patients: Technical Considerations

INTRODUCTION

The insula presents anatomic challenges to surgical exploration and intervention. Open neurosurgical intervention is associated with high rates of complications despite improved seizure control. Minimally invasive techniques using novel energy delivery methods have gained popularity due to their relative safety and ability to overcome access-related barriers. The goal of this paper is to present an operative technical report and methodological considerations on the application of magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) for the treatment of nonlesional, medically refractory, insular epilepsy in pediatric patients.

METHODS

Visualase laser probe(s) were implanted using ROSA robotic stereotactic guidance into the insula using a parasagittal trajectory. After confirmation of placement using intraoperative MRI, thermal energy was delivered under real-time MR guidance. Laser wire pullback was performed when the initial dose of thermal energy was insufficient to ablate the target in its entirety. Thermal ablation within the intended target was confirmed using gadolinium-enhanced brain MRI. Following removal of laser wires, a final T1-weighted axial brain MRI was performed to confirm no evidence of hemorrhage.

RESULTS

Three patients underwent MRgLITT of nonlesional insular epilepsy over an 11-month period. The epileptogenic focus was localized to the insula using stereoelectroencephalography. The anterior and middle portions of the insula were accessed using a parasagittal trajectory. Laser ablation was performed for up to 3 min using an output of 10.5 W. No complications were encountered, and all patients were discharged within 24 h after the surgery. At the most recent follow-up, all patients had an Engel I outcome without any new neurologic deficits.

CONCLUSION

This small cohort shows that insular ablation can be achieved safely with promising seizure outcomes in the short term.