Minimally Invasive Epilepsy Surgery

Abstract

Surgery remains a critical and often necessary intervention for a subset of patients with epilepsy. The overarching objective of surgical treatment has consistently been to enhance the quality of life for these individuals, either by achieving seizure freedom or by eliminating debilitating seizure types. This review specifically examines minimally invasive surgical approaches for epilepsy. Contemporary advancements have introduced a range of treatments that offer increased safety and efficacy compared to traditional open resective epilepsy surgeries. This manuscript provides a comprehensive review of these techniques and technologies.

Keywords

epilepsy surgery - minimally invasive epilepsy surgery - EEG

Introduction

Epilepsy surgery began in its modern form in 1861 when Sir Victor Horsley and Hughlings Jackson removed visible cortical lesions in three patients who had sustained previous cerebral trauma.[1] The first described patient in this cohort was a young man who experienced epilepsy onset at the age of 15 years after a roadway accident that occurred when he was 7 years old.[1] Horsley's prior experience with brain operations had been largely confined to animals. The patient was 22 years old at the time of the operation and had been suffering from frequent and prolonged episodes of status epilepticus with Jacksonian semiology.[1] As the operation commenced, a large cortical scar was visible, which was removed with 0.5 cm of surrounding tissue.[1] The young man initially experienced motor and sensory deficits; however, he fully recovered to his baseline and lived seizure-free thereafter. This remarkable feat was not without significant risk, as Horsley's first patients experienced a 5 to 7% mortality rate following surgery.[2] From this point forward, the technical evolution of epilepsy surgery has been nothing short of logarithmic. From this point forward, surgical practices have advanced in safety by minimizing adverse effects, risk of infection, and disruption of eloquent cortex. In the modern era, we now have tools and techniques that make minimally invasive epilepsy surgery feasible, safe, and effective. Minimally invasive surgical techniques for epilepsy surgery have lower morbidity, lower mortality, incur shorter hospitalizations, and pose less risk to the eloquent cortex. These technologies and techniques are reviewed below (see [Tables 1] and [2] for brief summaries).

Table 1 Strengths and limitations of technologies summarized

Technology	Strength(s)	Limitation(s)
EEG source imaging	Noninvasive. Able to apply to standard EEG.	Expertise dependent. Incorrectly chosen waveforms will also provide a localization.
High-quality MRI (7T or 3T plus artifact reduction)	Able to elucidate lesions in patients previously deemed MRI negative.	Expensive. Unable to offer to pediatric patients < 35 kg.
Positron emission tomography	Useful in nonlesional cases to identify epileptogenic zones via different modalities (metabolism).	Overestimates the true epileptogenic zone.
Single-photon emission computed tomography	Highly localizing if tracer is injected in the early ictal period.	Requires continuous monitoring and bedside staff member ready to inject tracer. Late injections can be misleading.
Magnetic source imaging/MEG	Source localizes signals “invisible” to EEG with tangential dipole. Noninvasive.	Expertise dependent. Cost to obtain and maintain MEG. Requires patient cooperation for mapping.
EEG-fMRI	Useful in cases of midline foci as discharges can appear generalized when in fact being focal. Also, useful in cases of subtle imaging abnormalities, fixation off sensitivity, and extensive structural abnormalities.	Not widely available, resource limited. Limited to research.
High-density EEG	Noninvasive. Can provide more precise localization and identification in cases that have a clear scalp EEG signal when compared with standard monitoring electrode paradigms.	Susceptible to artifact. Relatively expensive but less so than MEG. Requires expertise to use.

Abbreviations: EEG, electroencephalography; fMRI, functional magnetic resonance imaging; MEG, magnetoencephalography; MRI, magnetic resonance imaging.

Table 2 Strength and limitations of surgical techniques summarized

Technique	Strength(s)	Limitation(s)
Laser interstitial thermal therapy (LITT)	Able to target deep lesions and lesions that are small/adjacent to the eloquent cortex. Less pain, smaller incision, and shorter hospital admission time compared with open resection.	Limitations in recording radius from stereo EEG and ablation size.
Laser callosotomy	Minimal pain, less invasive, and shorter hospital admission time compared with open resection.	Palliative surgery for severe tonic and atonic seizures.
Laser functional hemispherotomy	Minimal pain, less invasive, and shorter hospital admission time compared with open resection.	Unable to target all interhemispheric connections. Works well in cases of existing large, lesional epilepsy compared with hemispherectomy or open modified hemispherotomy with subinsular window.
Radiofrequency thermocoagulation	Allows recording of ECOG using a stereotactic EEG probe and stimulation delivery through the same minimally invasive trajectory. Should be considered in patients with deep, difficult to access lesions, and may be considered in staged surgical approaches.	Suboptimal results despite the promising theoretical premise. Not all depth electrodes currently used for recording are approved for treatment.
Cryoablation	Incurs less risk to adjacent tissue compared with LITT.	Scarcely available. Few indications to pursue cryoablation > LITT outside of highly epileptogenic, vascular lesions.
Vagus nerve simulation therapy	Can be used in both focal and generalized drug-resistant epilepsies. Extracranial implantation reduces risk.	Predominantly a palliative strategy with low rates of seizure freedom. Need for future battery change.
Responsive neurostimulation	Able to be offered in many cases of nonoperative focal epilepsy with 1 or 2 foci. Able to record EEG and deliver stimulation. Can be used as a prelude to resective surgery (i.e., bilateral mesial temporal lobe epilepsy).	Limitation in the number of electrode contacts. Intracranial device with increased risk of adverse effects.
Deep brain stimulation	Can be offered to both focal and generalized refractory epilepsies.	Effects of chronic thalamic stimulation are unknown. Intracranial device with increased risk of adverse effects.

Abbreviations: EEG, electroencephalography; ECOG, electrocorticography.

Lesional versus Nonlesional Epilepsy and Treating the Epileptogenic Zone

Outcomes vary significantly between patients with epilepsy who have a visible lesion to target and those who are nonlesional.[3] The primary causes of lesional epilepsy in adults include hippocampal sclerosis (HS), low-grade developmental and epilepsy-associated brain tumors (LEAT), malformations of cortical development, and focal cortical dysplasias.[4] In children, there are fewer cases of HS as malformation of cortical development accounts for 39% of etiologies, followed by focal cortical dysplasia (27.07%), and LEAT (26.6%). HS accounts for 14.8% of pediatric cases.[4]

Historically, lesional cases of epilepsy have been addressed through open resective surgeries, boasting strong rates of seizure freedom (70% + ).[3] However, the associated morbidity of these surgeries is also significant. Data indicate that in long-term follow-up, nearly 35% of patients who undergo large open resections experience functional disability.[5] In the modern era, significant time and effort are dedicated to searching for the optimal intervention to offer a patient, aiming for seizure freedom or substantial seizure reduction while minimizing associated risks of harm.

Technologies to Consider to Increase Yield of Complete Seizure Freedom

Minimally invasive epilepsy surgery demands a high degree of accuracy, considering that vessels or eloquent cortex are frequently adjacent to the target tissue and cannot be sacrificed. The effectiveness of epilepsy surgery has been demonstrated to correlate with the quantity of congruent data that can be acquired from a patient. Emerging technologies and enhanced techniques provide additional avenues for assembling congruent data points, ultimately enhancing patient outcomes.

Electroencephalography Source Imaging

Electroencephalography (EEG) source localization, also known as EEG course imaging, involves utilizing the raw EEG signal to retroactively address the “inverse problem” and pinpoint the generator of a specific signal.[6] The process employs software—like Persyst—to extract mathematical data points from a recorded EEG.[7] Numerous signals have been identified as potentially useful in localizing the epileptogenic zone.[6] However, recent expert consensus suggests that a combination of manual interictal spike detection, automated interictal discharge detection, heralding spikes, direct current shifts, and early propagation pathways are the most valuable parameters to consider ([Fig. 1]).[6] The degree of congruence between these sets of data also confers greater certainty that the epileptogenic zone is accurately identified.

Fig. 1 (A) Laplacian EEG showcasing broad epileptiform discharges in the right central region that were poorly localizing on raw visual examination. (B) ESI of 53 averaged and manually selected spikes in the right central region pointing to a generator near the insular and right inferior frontal region. (C) MRI brain with right periventricular nodular heterotopia responsible for epilepsy.

High-Quality Magnetic Resonance Imaging

Given the disparity between patients with lesional versus nonlesional causes of epilepsy, a primary goal in evaluation is to ensure that, upon close inspection, a patient does not have an identifiable lesion. New technology, such as 7 tesla magnetic resonance imaging (MRI), has clearly demonstrated that cases that appear to be nonlesional on 3 tesla can be resolved with the use of a stronger magnet and a more detailed scan ([Fig. 2]).[8] However, high-strength MRI scans may not be suitable for all patients, especially pediatric cases, due to the heat generated during the scan and the fine resolution that is highly susceptible to motion artifacts.[9] Most patients require full sedation, and the brain must be large enough to withstand the heat without MRI-induced injury. Additionally, the cost of a new MRI can be prohibitive in many centers. To address these challenges, 3 tesla scanners can be retrofitted with new software, reducing imaging artifacts and creating visually crisp scans similar to those of a 7 tesla or greater strength scan.[10] These software packages and MRI updates can be deployed when a 7 tesla MRI or greater is unavailable.

Fig. 2 A patient who was able to have successful stereotactic epilepsy surgery after a 7T MRI elucidated a lesion that was unappreciable on 3T MRI.

Positron Emission Tomography

Positron emission tomography (PET) generates a visual image representative of brain metabolism.[11] Most commonly, fluorodeoxyglucose brain PET employs a radioisotope glucose analog to measure glucose metabolism.[11] In the context of epilepsy surgery evaluation, the scan may reveal increased signal, diminished signal, or a total lack of signal. Both hypermetabolism and hypometabolism may assist in identifying tissue associated with the epileptogenic zone. Before conducting a PET study, it can be beneficial to record patients with EEG, while the radiolabeled tracer is injected to fully understand whether the study reflects an ictal or interictal state. Importantly, a PET study measuring metabolism helps regionalize an epileptogenic focus but often overestimates the visually represented amount of involved tissue.[11] PET can be especially useful in cases of nonlesional epilepsy where localization may be challenging both on EEG and MRI.[11]

Single-Photon Emission Computed Tomography

Single-photon emission computed tomography (SPECT) is typically employed to identify seizure onset.[12] The technique involves administering a tracer at the onset of the ictus. The tracer visually points to the seizure focus by identifying relative hyperperfusion compared with the rest of the brain ([Fig. 3]).[12] Ictal SPECT has demonstrated accuracy in correctly identifying epileptogenic foci, with a success rate of 97% in cases of unilateral temporal lobe epilepsy and 90% in extratemporal epilepsies.[13] Its primary limitations lie in cost and availability, as storing the tracer is challenging and injecting it requires monitoring by both radiology technologists and EEG technologists.

Fig. 3 Ictal Axial SPECT scan showcasing clear hypermetabolism in the right insular region.

Magnetoencephalography

Magnetoencephalography (MEG) is a technology employed in pediatric and adult epilepsies to record magnetic fields produced by electric currents in the brain. MEG can pinpoint epileptogenic zones, lateralize language functions, localize sensorimotor cortex, and identify visually evoked fields ([Fig. 4]).[14] The magnetic field is perpendicular to the electric field recorded by EEG. Therefore, in cases where the dipole of a discharge is tangential, EEG may not produce a signal, but MEG will.[14] This uniqueness makes MEG a valuable technology that can provide congruent data when EEG does not offer helpful information. The cost of MEG units is decreasing over time, and the utility of the technology appears to be on the rise.[14] New MEG units offer simultaneous EEG and MEG recordings. This combined technology potentially offers a new horizon of data that can help patients but has largely yet to be studied in depth.

Fig. 4 Magnetoencephalography with red circles highlighting interictal clusters of epileptiform discharges and yellow triangles highlighting area activated in receptive language paradigm.

Electroencephalography-Functional Magnetic Resonance Imaging

Electroencephalography-functional magnetic resonance imaging (EEG-fMRI), as the name suggests, simultaneously records signals from EEG and hemodynamic changes in the brain.[15] This technology can be beneficial in challenging cases of epilepsy localization, instances of fixation off sensitivity, and cases of focal epilepsy that mimic generalized discharges on EEG.[15] [16] A small signal on EEG can be correlated with fMRI blood-oxygen-level-dependent (BOLD) signal changes that in turn, give more credence to a signal observed. A study by Coan et al demonstrated that EEG-fMRI data led to BOLD changes on fMRI within 2 cm of the epileptogenic zone, with a positive predictive value of 78%.[17] This technology is important to be aware of and needs to be researched more.

High-Density Electroencephalography

In contrast to the standard electrode channels used in surface EEG recordings, high-density EEG utilizes at least 64 channels allowing for higher spatial analysis of discharges.[18] A case series by Stoyell et al demonstrated its advantage in localizing or lateralizing interictal discharges when standard EEG, SPECT, PET, and fMRI failed to do so and positively impacting the next phase of surgical planning in selected children.[18] Limitation includes its laboriousness in implementation and interpretation time.[18] Patients typically need over 100 channels and the utilization of additional software technology for interpretation.[18]

Minimally Invasive Procedures

Laser Interstitial Thermal Therapy

Laser interstitial thermal therapy (LITT) is a tool frequently included in the modern repertoire of level IV epilepsy centers. When compared with open resections, LITT has its own strengths and limitations ([Fig. 6]).[19] Generally, LITT offers a much safer risk profile to patients than open resection.[19] Patients tolerate the procedure better and can leave the hospital in less time compared with open resections. LITT is also advantageous for targeting deep lesions and areas that would otherwise be challenging to address with resections, involving significant operative risk.[19]

In an LITT ablation, a laser emits light energy, heating and damaging brain tissue. In the modern era, LITT ablations are performed simultaneously with MRI.[19] New LITT lasers can create a treatment radius between 1 and 2 cm from the laser tip. To prevent damage to tissues outside the intended treatment area, the Arrhenius equation is employed. This formula determines the temperature dependence of reaction rates, identifying the zone of cell death as a measure of protein denaturation due to the laser's temperature and duration.[19] The laser can target and treat both lesional and nonlesional causes of epilepsy.[19]

Previous research has demonstrated the efficacy of LITT in cases of both lesional and nonlesional epilepsy.[19] Seizure freedom rates for lesional temporal lobe epilepsy exceed 58%, reaching upwards of 66% in cases of mesial temporal sclerosis.[20] The success rate outside of lesional temporal lobe epilepsy is lower but improving over time with enhanced technology and a greater emphasis on data congruence.

In appropriate cases, stereotactic EEG (sEEG) placement precedes potential LITT therapy.[21] sEEG involves the placement of depth electrodes to record brain activity. These depth electrodes, with varying numbers of contacts and lengths, are minimally invasive compared with the traditional placement of EEG subdural grids and strips used in open resections. Importantly, sEEG does not require a traditional craniotomy. This method enables the targeting of deep brain regions that would otherwise be challenging to record. Multiple depth electrodes can be implanted in an array to understand a specific localized region of the brain or to explore different anatomic structures relevant to the genesis or treatment of seizures.

One primary limitation of sEEG recording is the relatively small spatial resolution of electrical activity sampled, covering approximately 7 mm of tissue.[22] Consequently, there may be anticipated gaps in EEG recordings that need to be planned for. The number of depth electrodes used is significant, as each placement incurs a 1% risk of intracranial hemorrhage.[23] Historically, the success rate of sEEG LITT therapy in rendering patients seizure-free has been around 30 to 35% for all types of epilepsy.[24] In the modern era, a well-formed hypothesis and emphasis on concordant presurgical data can lead to improved rates of seizure freedom and freedom from disabling seizure types.

Laser Corpus Callosotomy

A corpus callosotomy via LITT offers a safe alternative to the traditional approach involving open resection.[25] This palliative procedure aims to limit dangerous seizure types, particularly drop attacks, by removing the majority of interhemispheric connections. The disconnected corpus callosum serves to restrict the spread of seizure generalization. An inherent concern after severing the corpus callosum is the potential development of a disconnection syndrome.[25] Patients may experience this syndrome only in the acute period or chronically, with deficits in spontaneous speech, incontinence, and paresis of the nondominant leg being primary concerns. Disconnection syndrome generally occurs in older patients undergoing total corpus callosotomy.[26] Despite this concern, the surgery can still be effectively and safely performed in older individuals by sparing the posterior corpus callosum and only severing the anterior aspect.[26]

A 2022 systematic review of laser ablation for corpus callosotomy found the procedure to be feasible and safe with a low risk of developing disconnection syndrome.[26] Patients experienced low complication rates with no sacrifice of seizure control compared with traditional callosotomy.[26] The majority of patients undergoing the procedure for atonic seizures achieved complete seizure freedom or a dramatically reduced seizure burden.[26]

Laser Hemispherotomy

LITT can effectively be employed for minimally invasive functional hemispherotomies.[27] By utilizing multiple laser trajectories, LITT can disconnect the temporal lobe, insula, complete corpus callosum, and the descending corticospinal and frontobasal projections ([Fig. 5]).[28] Employing LITT for hemispherotomy eliminates the need for a large hemicraniectomy, significantly reducing associated infection, pain, and duration of hospital stay.[28] Results are particularly encouraging in appropriate cases, such as those involving patients with large perinatal middle cerebral artery infarcts. This patient selection is crucial, as the ischemic insult itself often destroys insular structures, which typically require surgical removal or disconnection in traditional hemispherotomies.[28]

Fig. 5 Laser hemispherotomy technique summarized in images.

Radiofrequency Thermocoagulation

Radiofrequency (RF) thermocoagulation, or RF-ablation, is a treatment that employs high-frequency current to target specific tissue.[29] A key advantage of RF-ablation is its ability to simultaneously record EEG using an sEEG probe, deliver stimulation, and treat through the same minimally invasive trajectory.[29] In theory, this approach allows for targeting and stimulating a lesion, with induced seizures indicating proximity to the seizure onset zone. Subsequently, treatment can be administered, and the stimulation process repeated.[29] While theoretically sound, immediate and long-term patient follow-up has revealed suboptimal results. In challenging nonlesional cases, this technique may provide a safe means to target a hypothesized epileptogenic zone lacking concordant preoperative data.[29]

Cryoablation

Cryoablation in epilepsy surgery is a seldom-used technique. It involves using low temperatures to freeze tissue, inducing cellular shrinkage, dehydration, and eventual cell death. The procedure entails inserting a catheter into the targeted treatment region.[30] Cryoablation employs argon gas, which, when expanded, creates temperatures ranging from −20 to −50°C.[30] These extreme temperatures form an ice ball that freezes the designated tissue. As the ice ball thaws, fluid returns to dehydrated cells, causing them to lyse. While cryoablation is not widely adopted, its theoretical advantages are noteworthy. Using cold temperatures instead of heat poses fewer risks to adjacent tissue, especially vasculature.[30] The ice ball formed is not susceptible to a bloom effect, as is the case with the heat used in LITT.[30] Limitations include a delayed effect, exposure to ionizing radiation, and less demarcated lesion borders.[30]

Minimally Invasive Nonresective Palliative Procedures

Vagus Nerve Stimulation

Vagus nerve stimulation (VNS) and its effects on the brain were first reported in 1985 by Zabara et al, who found that electrical stimulation from the vagus nerve produced an inhibition of neural processes. VNS can be used in diseases outside of epilepsy and has advantages in mood disorders. The exact mechanism by which VNS targets epilepsy control remains incompletely understood at this time.[31] One hypothesis stems from the observation that VNS induces EEG desynchronization in animal models.[31] The VNS stimulator is implanted in the chest, and a wire is fed into the patient's neck, where it is carefully wound around the vagus nerve.[32] The stimulator is programmable and can deliver both constant stimulation and pulse stimulation during tachycardia.[32] The system is responsive to a magnet swipe and has the capability to deliver stimulation with the swipe of a magnet when the patient is experiencing a seizure in the hopes of aborting or reducing its duration and severity.[32]

Data support VNS efficacy for the treatment of drug-resistant epilepsy. Most studies cite a responder rate of nearly 35 to 55% (defined as a 50% seizure reduction) to VNS.[33] The number of patients achieving seizure freedom with the addition of VNS is small, between 0 and 21%.[33] The VNS system is generally safe, but like all implanted devices, it carries an associated risk of site infection (4%).[33] Thirty-seven percent of patients experience hoarseness associated with stimulation delivered through VNS.[33]

Responsive Neurostimulation

Responsive neurostimulation (RNS) is a form of neuromodulation that incorporates mechanisms similar to VNS but differs in its ability to provide localized treatment while recording EEG from the sampled area.[34] The RNS system consists of a neurostimulator device implanted in the patient's skull. Electrodes, connected to the stimulator, are strategically placed inside the brain to target focal seizures.[34] These implanted electrodes record EEG, and when the electrographic pattern of interest is detected, the stimulator delivers treatment through brief electrical pulses to disrupt the organizing and evolving epileptic activity. The efficacy of RNS is felt to be related to cumulative neuromodulatory effects over time compared with acute abortive treatment.[35]

A 2021 systematic review on VNS, RNS, and deep brain stimulation (DBS) found that RNS achieves a seizure reduction of >54%, increasing over time in 2-year, 5-year, and 9-year follow-ups. Seizure freedom also increases correspondingly, with 8.7% of patients getting seizure-free at 2 years, 16.2% at 5 years, and 21.1% at 9 years.[33]

However, the side effect profile of RNS is not entirely benign and is important to be aware of. According to the same systematic review, 2.7% of RNS cases were complicated by nonseizure-related hemorrhage, and memory impairment was evident in 12.7% of patients after RNS insertion.[33] A recent study showed less likely to have cognitive impairments with RNS versus resection in dominant temporal lobe surgery.[36] The rate of infection increases over time at the 2, 5, and 9-year marks (4/9/12%).[33]

The unique recording capabilities of the RNS system may present opportunities for improvement in the future. In particular, RNS for bilateral mesial temporal lobe epilepsies provides data from chronic electrocorticography to determine a laterality ratio which may allow for palliative unilateral temporal lobe surgery to improve outcomes.[37] At epilepsy centers with experience and through ongoing clinical trials, RNS is also being used for direct thalamic stimulation for intractable generalized epilepsies, focal epilepsies, and Lennox–Gastaut syndrome.

Deep Brain Stimulation

DBS is a form of neurostimulation that targets epilepsy by stimulating the thalamus, a critical structure believed to play an integral role in generalized epilepsies through network connectivity and seizure propagation.[38] Historically, multiple nuclei have been targeted in DBS for epilepsy treatment, including the anterior nucleus, centromedian, dorsomedial, and pulvinar.[38] The stimulation of the anterior nucleus is the only U.S. Food and Drug Administration-approved procedure for focal epilepsies.[39] More recent studies have focused on the importance of nucleus selection relative to epilepsy type. In addition, high-resolution neuroimaging has allowed more accurate targeting of specific thalamic nuclei and subnuclei. These advancements in technique may lead to improved outcomes in comparison to prior studies. Further, accurately targeting these nuclei and subnuclei within the thalamus requires high-resolution neuroimaging. This has been a limitation of prior studies of DBS and may have underestimated the true efficacy given inaccurate implantations.[40] [41]

Historically, DBS has shown rates similar to RNS, with approximately 50% of patients achieving a 50% or more reduction in seizures. A systematic review found that over time, 7.4% of patients achieved seizure freedom after 2 years, 10.1% after 5 years, and 9.2% after 7 years.[33] About 28% of patients implanted with DBS experienced memory impairment at their 5-year follow-up and 13% experienced an increased rate of depression, likely related to modulation of the anterior nucleus.[33] However, the side effects and long-term effects of DBS, especially in the context of pediatric patients with epilepsy, largely remain unknown.

Open Surgery

Selective Amygdalohippocampectomy

Selective amygdalohippocampectomy is a modified surgical approach that strives for minimal invasiveness compared with its predecessor, anterior temporal lobectomy (ATL). An ALT poses the risk of speech issues. In cases of dominant ATL for epilepsy, there is a specific risk to naming ability after surgery.[42] As the name suggests, selective amygdalohippocampectomy involves resection of specific parts of the hippocampus and amygdala.[43] This type of operation is indicated for patients with mesial temporal lobe epilepsy, with the highest rates of success observed in lesional cases.[43] In the past, this operation was offered to patients with concordant information strongly suggesting mesial temporal lobe localization. However, an open operation like this has largely fallen to the wayside with the rise of LITT, which can effectively target the mesial structures with much less disruption to the skull. In many epilepsy centers, LITT may be offered to cases of suspected mesial temporal lobe epilepsy, with ATL as a backup option.

Endoscopic Surgical Techniques

Endoscopic Corpus Callosotomy and Hemispherotomy

As previously mentioned, corpus callosotomy is considered to be palliative to provide patients with measurable relief from injuries related to generalized seizure types.[44] Resulting complications include disconnection syndromes. Hemispherotomies have a similar effect by functionally disconnecting the left and right brain via hippocampus or affected lobes and projections from the remainder of the brain.[44] Since the early 20th century, this was traditionally done via an open surgical technique. To minimize incision size, the need for larger craniotomies, and excessive cortical and vessel manipulation, endoscopic corpus callosotomy and hemispherotomy techniques are being utilized.[44] While the risk of complications remains lower than an open technique, there are technical limitations related to endoscope maneuvering and differing operator preferences. Complication rates are generally less than <5%; however, morbidity rate varies by type and extent of surgery.[44]

Conclusion

Epilepsy surgery is a critical treatment for an indicated and, in many cases, necessary cohort of people with epilepsy. The type of treatments offered have never changed in their overall goal: to help increase the quality of life for patients with epilepsy through seizure freedom, or freedom from disabling seizure type. The new-age technologies and techniques reviewed will hopefully continue to be researched and perfected to provide excellent outcomes to a greater percentage of people undergoing epilepsy surgery.

Fig. 6 Traditional open surgery versus LiTT. An open resection of a right temporal lobe epileptogenic focus is shown (A). Note the large resection cavity (green star) and surrounding parenchymal edema/facial tissue edema. The segulae of a LiTT procedure on an occipital lobe epileptogenic focus is shown (B). Note the absence of significant edema both in the parenchyma and surrounding tissues.

Conflict of Interest

None declared.

Ethical Approval

Ethical approval and informed consent were not sought as the manuscript is a review article which does not use patient-identifiable information and did not collect research or data collection.

• References

• 1 Schijns OE, Hoogland G, Kubben PL, Koehler PJ. The start and development of epilepsy surgery in Europe: a historical review. Neurosurg Rev 2015; 38 (03) 447-461
• 2 Feindel W, Leblanc R, de Almeida AN. Epilepsy surgery: historical highlights 1909-2009. Epilepsia 2009; 50 (Suppl. 03) 131-151
• 3 Téllez-Zenteno JF, Hernández Ronquillo L, Moien-Afshari F, Wiebe S. Surgical outcomes in lesional and non-lesional epilepsy: a systematic review and meta-analysis. Epilepsy Res 2010; 89 (2-3): 310-318
• 4 López-Rivera JA, Smuk V, Leu C. et al. Incidence and prevalence of major epilepsy-associated brain lesions. Epilepsy Behav Rep 2022; 18: 100527
• 5 Hoppe C, Beeres K, Witt JA, Sassen R, Helmstaedter C. Clinical adult outcome 11-30 years after pediatric epilepsy surgery: complications and other surgical adverse events, seizure control, and cure of epilepsy. Epilepsia 2023; 64 (02) 335-347
• 6 Ebersole JS. EEG source imaging in presurgical evaluations. J Clin Neurophysiol 2024; 41 (01) 36-49
• 7 Vogrin SJ, Plummer C. EEG source imaging-clinical considerations for EEG acquisition and signal processing for improved temporo-spatial resolution. J Clin Neurophysiol 2024; 41 (01) 8-18
• 8 Wang I, Oh S, Blümcke I. et al. Value of 7T MRI and post-processing in patients with nonlesional 3T MRI undergoing epilepsy presurgical evaluation. Epilepsia 2020; 61 (11) 2509-2520
• 9 Burkett BJ, Fagan AJ, Felmlee JP. et al. Clinical 7-T MRI for neuroradiology: strengths, weaknesses, and ongoing challenges. Neuroradiology 2021; 63 (02) 167-177
• 10 Qu L, Zhang Y, Wang S, Yap P-T, Shen D. Synthesized 7T MRI from 3T MRI via deep learning in spatial and wavelet domains. Med Image Anal 2020; 62: 101663
• 11 Rathore C, Dickson JC, Teotónio R, Ell P, Duncan JS. The utility of 18F-fluorodeoxyglucose PET (FDG PET) in epilepsy surgery. Epilepsy Res 2014; 108 (08) 1306-1314
• 12 Knowlton RC. The role of FDG-PET, ictal SPECT, and MEG in the epilepsy surgery evaluation. Epilepsy Behav 2006; 8 (01) 91-101
• 13 Yassin A, El-Salem K, Al-Mistarehi AH. et al. Use of innovative SPECT techniques in the presurgical evaluation of patients with nonlesional extratemporal drug-resistant epilepsy. Mol Imaging 2021; 2021: 6614356
• 14 Nordli III DR, Galan FN. Pediatric magnetoencephalography. Ann Child Neurol Soc 2023; 1 (02) 123-128
• 15 Zijlmans M, Huiskamp G, Hersevoort M, Seppenwoolde J-H, van Huffelen AC, Leijten FS. EEG-fMRI in the preoperative work-up for epilepsy surgery. Brain 2007; 130 (Pt 9): 2343-2353
• 16 Nordli III DR, Collins J, Warnke P, Nordli Jr DR. Paradigm found: epileptogenic zone identified by fMRI in ictal fixation off sensitivity. Epileptic Disord 2024; 26 (02) 244-249
• 17 Coan AC, Chaudhary UJ, Grouiller F. et al. EEG-fMRI in the presurgical evaluation of temporal lobe epilepsy. J Neurol Neurosurg Psychiatry 2016; 87 (06) 642-649
• 18 Stoyell SM, Wilmskoetter J, Dobrota MA. et al. High density EEG in current clinical practice and opportunities for the future. J Clin Neurophysiol 2021; 38 (02) 112-123
• 19 Prince E, Hakimian S, Ko AL, Ojemann JG, Kim MS, Miller JW. Laser interstitial thermal therapy for epilepsy. Curr Neurol Neurosci Rep 2017; 17 (09) 63
• 20 Cajigas I, Kanner AM, Ribot R. et al. Magnetic resonance–guided laser interstitial thermal therapy for mesial temporal epilepsy: a case series analysis of outcomes and complications at 2-year follow-up. World Neurosurg 2019; 126: e1121-e1129
• 21 Gupta K, Cabaniss B, Kheder A. et al. Stereotactic MRI-guided laser interstitial thermal therapy for extratemporal lobe epilepsy. Epilepsia 2020; 61 (08) 1723-1734
• 22 Lhatoo S, Lacuey N, Ryvlin P. Principles of stereotactic electroencephalography in epilepsy surgery. J Clin Neurophysiol 2016; 33 (06) 478-482
• 23 McGovern RA, Ruggieri P, Bulacio J, Najm I, Bingaman WE, Gonzalez-Martinez JA. Risk analysis of hemorrhage in stereo-electroencephalography procedures. Epilepsia 2019; 60 (03) 571-580
• 24 Gotman J, Chauvel P, Pickard AA. et al. A Practical Approach to Stereo EEG. 1st ed.. New York: Springer Publishing Company; 2020
• 25 Palma AE, Wicks RT, Popli G, Couture DE. Corpus callosotomy via laser interstitial thermal therapy: a case series. J Neurosurg Pediatr 2018; 23 (03) 303-307
• 26 Awad AJ, Kaiser KN. Laser ablation for corpus callosotomy: systematic review and pooled analysis. Seizure 2022; 96: 137-141
• 27 Chua MM, Stone SS, Patel A, Madsen JR. Functional hemispherotomy using magnetic resonance (MR)-guided laser induced thermal therapy (LITT). Neurosurgery 2020 (e-pub ahead of print)
• 28 Mendoza-Elias N, Satzer D, Henry J, Nordli Jr DR, Warnke PC. Tailored hemispherotomy using tractography-guided laser interstitial thermal therapy. Oper Neurosurg (Hagerstown) 2023; 24 (06) e407-e413
• 29 Voges J, Büntjen L, Schmitt FC. Radiofrequency-thermoablation: general principle, historical overview and modern applications for epilepsy. Epilepsy Res 2018; 142: 113-116
• 30 Patil AA, de Joya J. Minimally invasive surgical techniques in patients with intractable epilepsy with CT-guided stereotactic cryoablation as a superior alternative: a systematic review. Egypt J Neurosurg 2022; 37 (01) 35
• 31 George MS, Nahas Z, Bohning DE. et al. Mechanisms of action of vagus nerve stimulation (VNS). Clin Neurosci Res 2004; 4 (1–2): 71-79
• 32 Ben-Menachem E. Vagus-nerve stimulation for the treatment of epilepsy. Lancet Neurol 2002; 1 (08) 477-482
• 33 Skrehot HC, Englot DJ, Haneef Z. Neuro-stimulation in focal epilepsy: a systematic review and meta-analysis. Epilepsy Behav 2023; 142: 109182
• 34 Sun FT, Morrell MJ. The RNS system: responsive cortical stimulation for the treatment of refractory partial epilepsy. Expert Rev Med Devices 2014; 11 (06) 563-572
• 35 Chiang S, Khambhati AN, Wang ET, Vannucci M, Chang EF, Rao VR. Evidence of state-dependence in the effectiveness of responsive neurostimulation for seizure modulation. Brain Stimul 2021; 14 (02) 366-375
• 36 O'Donnell CM, Anderson CT, Oleksy AJ, Swanson SJ. A comparison of neuropsychological outcomes following responsive neurostimulation and anterior temporal lobectomy in drug-resistant epilepsy. Brain Sci 2023; 13 (12) 1628
• 37 Chiang S, Fan JM, Rao VR. Bilateral temporal lobe epilepsy: how many seizures are required in chronic ambulatory electrocorticography to estimate the laterality ratio?. Epilepsia 2022; 63 (01) 199-208
• 38 Li MCH, Cook MJ. Deep brain stimulation for drug-resistant epilepsy. Epilepsia 2018; 59 (02) 273-290
• 39 Salanova V, Sperling MR, Gross RE. et al. SANTÉ Study Group. The SANTÉ study at 10 years of follow-up: effectiveness, safety, and sudden unexpected death in epilepsy. Epilepsia 2021; 62 (06) 1306-1317
• 40 Gross RE, Fisher RS, Sperling MR, Giftakis JE, Stypulkowski PH. Analysis of deep brain stimulation lead targeting in the stimulation of anterior nucleus of the thalamus for epilepsy clinical trial. Neurosurgery 2021; 89 (03) 406-412
• 41 Freund BE, Greco E, Okromelidze L. et al. Clinical outcome of imaging-based programming for anterior thalamic nucleus deep brain stimulation. J Neurosurg 2022; 138 (04) 1008-1015
• 42 Saykin AJ, Stafiniak P, Robinson LJ. et al. Language before and after temporal lobectomy: specificity of acute changes and relation to early risk factors. Epilepsia 1995; 36 (11) 1071-1077
• 43 Hoyt AT, Smith KA. Selective Amygdalohippocampectomy. Neurosurg Clin N Am 2016; 27 (01) 1-17
• 44 Sood S, Marupudi NI, Asano E, Haridas A, Ham SD. Endoscopic corpus callosotomy and hemispherotomy. J Neurosurg Pediatr 2015; 16 (06) 681-686

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Eingereicht: 15. April 2024

Angenommen: 18. Juni 2024

Artikel online veröffentlicht:
10. Juli 2024