Surgical technique

Characterizing Frontal Lobe Seizure Semiology in Children

OBJECTIVE

The objective was to analyze seizure semiology in pediatric frontal lobe epilepsy patients, considering age, to localize the seizure onset zone for surgical resection in focal epilepsy.

METHODS

Fifty patients were identified retrospectively, who achieved seizure freedom after frontal lobe resective surgery at Great Ormond Street Hospital. Video-electroencephalography recordings of preoperative ictal seizure semiology were analyzed, stratifying the data based on resection region (mesial or lateral frontal lobe) and age at surgery (≤4 vs >4).

RESULTS

Pediatric frontal lobe epilepsy is characterized by frequent, short, complex seizures, similar to adult cohorts. Children with mesial onset had higher occurrence of head deviation (either direction: 55.6% vs 17.4%; p = 0.02) and contralateral head deviation (22.2% vs 0.0%; p = 0.03), ictal body-turning (55.6% vs 13.0%; p = 0.006; ipsilateral: 55.6% vs 4.3%; p = 0.0003), and complex motor signs (88.9% vs 56.5%; p = 0.037). Both age groups (≤4 and >4 years) showed hyperkinetic features (21.1% vs 32.1%), contrary to previous reports. The very young group showed more myoclonic (36.8% vs 3.6%; p = 0.005) and hypomotor features (31.6% vs 0.0%; p = 0.003), and fewer behavioral features (36.8% vs 71.4%; p = 0.03) and reduced responsiveness (31.6% vs 78.6%; p = 0.002).

INTERPRETATION

This study presents the most extensive semiological analysis of children with confirmed frontal lobe epilepsy. It identifies semiological features that aid in differentiating between mesial and lateral onset. Despite age-dependent differences, typical frontal lobe features, including hyperkinetic seizures, are observed even in very young children. A better understanding of pediatric seizure semiology may enhance the accuracy of onset identification, and enable earlier presurgical evaluation, improving postsurgical outcomes. ANN NEUROL 2024;95:1138-1148.

Feasibility and safety of stereoelectroencephalography in young children

PURPOSE

Stereoelectroencephalography (SEEG) is a diagnostic surgery that implants electrodes to identify areas of epileptic onset in patients with drug-resistant epilepsy (DRE). SEEG is effective in identifying the epileptic zone; however, placement of electrodes in very young children has been considered contraindicated due to skull thinness. The goal of this study was to evaluate if SEEG is safe and accurate in young children with thin skulls.

METHODS

Four children under the age of two years old with DRE underwent SEEG to locate the region of seizure onset. Presurgical planning and placement of electrodes were performed using ROSA One Brain. Preoperative electrode plans were merged with postoperative CT scans to determine accuracy. Euclidean distance between the planned and actual trajectories was calculated using a 3D coordinate system at both the entry and target points for each electrode.

RESULTS

Sixty-three electrodes were placed among four patients. Mean skull thickness at electrode entry sites was 2.34 mm. The mean difference between the planned and actual entry points was 1.12 mm, and the mean difference between the planned and actual target points was 1.73 mm. No significant correlation was observed between planned and actual target points and skull thickness (Pearson R =  - 0.170). No perioperative or postoperative complications were observed.

CONCLUSIONS

This study demonstrates that SEEG can be safe and accurate in children under two years of age despite thin skulls. SEEG should be considered for young children with DRE, and age and skull thickness are not definite contraindications to the surgery.

Use of Compressed Sensing Accelerated, Low-Velocity Encoded, Isotropic Resolution, Phase Contrast Magnetic Resonance Angiography for SEEG Electrode Implantation

OBJECTIVE

We assessed the feasibility of using compressed sensing accelerated, low-velocity encoded, isotropic resolution phase contrast (CLIP) magnetic resonance angiography (MRA) for avascular trajectory planning of stereoelectroencephalography.

METHODS

Ten healthy subjects (1 woman and 9 men; age, 33.6 ± 9.0 years) and 20 consecutive patients (12 female patients; age, 22 ± 13.6 years) were enrolled in the present study. The healthy subjects underwent CLIP-MRA, and 3 other phase contrast MRA protocols with conventional parallel imaging (PI) acceleration, including low resolution with twofold PI (PI2), high resolution (HR) with fivefold PI (PI5), and HR-PI2. The patients underwent CLIP-MRA and computed tomography angiography (CTA). The image qualities were evaluated. The numbers and locations of trajectory-vessel conflict detected using CLIP-MRA were noted.

RESULTS

With similar scan durations, CLIP-MRA achieved higher spatial resolution compared with low resolution with PI2 and detected significantly more branches compared with HR-PI5. With the same spatial resolution, the signal/noise and contrast/noise ratios of CLIP-MRA were higher than those with HR-PI2 with a shorter scan duration. For the 12 adult patients (10 female patients; 28.8 ± 12.7 years), CLIP-MRA had better signal/noise and contrast/noise ratios than CTA. The trajectory had required modification for 14 of the 20 patients (70%), with a proportion of trajectory modification of 10.7% (23 of 215 electrodes). The middle meningeal artery, cortical vessel, and skull vessel were the main vessels with conflict (n = 11, n = 7, and n = 5, respectively).

CONCLUSIONS

In the present study, CLIP-MRA provided a clear cortical vascular display noninvasively without intravascular contrast and radiation. The middle meningeal artery and diploic and emissary veins were the main conflict vessels and could be clearly displayed using CLIP-MRA but not CTA.

Surgical candidates in children with epileptic spasms can be selected without invasive monitoring: A report of 70 cases

OBJECTIVE

Prior surgical series in children with drug-resistant epileptic spasms have reported use of intracranial EEG monitoring in up to two-third of patients. We report outcome after epilepsy surgery for drug-resistant epileptic spasms in a cohort of children without the use of intracranial EEG monitoring in any of the patients.

METHODS

Medical records of all consecutive children aged 5 years or under who had epilepsy surgery for epileptic spasms at Cleveland Clinic between 2000 and 2018 were reviewed. Post-operative seizure outcome and predictors of prognosis of seizure outcome were analyzed.

RESULTS

Seventy children with active epileptic spasms underwent surgical resections during the study period. Mean age at seizure onset was 6.8 (+9.31) months and median age at surgery was 18.5 months. An epileptogenic lesion was identified on brain MRI in all patients; 17 (24%) had bilateral abnormalities. Etiologies included malformations of cortical development (58%), perinatal infarct/encephalomalacia (39%), and tumor (3%). None of the patients had intracranial EEG. Surgical procedures included hemispherectomy (44%), lobectomy/ lesionectomy (33%), and multilobar resections (23%). Twelve children needed repeat surgery; six (50%) became seizure free after the second surgery. At six months follow-up, 73% (51/70) were seizure-free since surgery. At a mean follow-up of 4.7 years, 60% (42/70) had Engel 1 outcome. In those with seizure recurrence, 17 (60%) reported improvement. Shorter epilepsy duration (p = 0.05) and lobar or sub-lobar epileptogenic lesions (p = 0.02) predicted favorable seizure outcome at 6 months after surgery. For long term outcome, patients with bilateral abnormalities on MRI (p = 0.001), and multilobar extent on MRI (p = 0.02) were at higher risk for recurrence.

SIGNIFICANCE

Children with drug-resistant epileptic spasms secondary to an epileptogenic lesion detected on MRI could be selected for epilepsy surgery without undergoing intracranial EEG monitoring. A surgical selection paradigm without intracranial monitoring may allow early surgery without the risks of invasive monitoring.

VarioGuide® frameless neuronavigation-guided stereoelectroencephalography in adult epilepsy patients: technique, accuracy and clinical experience

Background

Stereoelectroencephalography (SEEG) allows the identification of deep-seated seizure foci and determination of the epileptogenic zone (EZ) in drug-resistant epilepsy (DRE) patients. We evaluated the accuracy and treatment-associated morbidity of frameless VarioGuide® (VG) neuronavigation-guided depth electrode (DE) implantations.

Methods

We retrospectively identified all consecutive adult DRE patients, who underwent VG-neuronavigation DE implantations, between March 2013 and April 2019. Clinical data were extracted from the electronic patient charts. An interdisciplinary team agreed upon all treatment decisions. We performed trajectory planning with iPlan® Cranial software and DE implantations with the VG system. Each electrode’s accuracy was assessed at the entry (EP), the centre (CP) and the target point (TP). We conducted correlation analyses to identify factors associated with accuracy.

Results

The study population comprised 17 patients (10 women) with a median age of 32.0 years (range 21.0–54.0). In total, 220 DEs (median length 49.3 mm, range 25.1–93.8) were implanted in 21 SEEG procedures (range 3–16 DEs/surgery). Adequate signals for postoperative SEEG were detected for all but one implanted DEs (99.5%); in 15/17 (88.2%) patients, the EZ was identified and 8/17 (47.1%) eventually underwent focus resection. The mean deviations were 3.2 ± 2.4 mm for EP, 3.0 ± 2.2 mm for CP and 2.7 ± 2.0 mm for TP. One patient suffered from postoperative SEEG-associated morbidity (i.e. conservatively treated delayed bacterial meningitis). No mortality or new neurological deficits were recorded.

Conclusions

The accuracy of VG-SEEG proved sufficient to identify EZ in DRE patients and associated with a good risk-profile. It is a viable and safe alternative to frame-based or robotic systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-021-04755-w.

Technical Aspects of SEEG and Its Interpretation in the Delineation of the Epileptogenic Zone

Stereo-electroencephalography (SEEG) has gained global popularity in recent years. In Japan, a country in which invasive studies using subdural electrodes (SDEs) have been the mainstream, SEEG has been approved for insurance coverage in 2020 and is expected to gain in popularity. Some concepts supporting SEEG methodology are fundamentally different from that of SDE studies. Clinicians interested in utilizing SEEG in their practice should be aware of those aspects in which they differ. Success in utilizing the SEEG methodology relies heavily on the construction of an a priori hypothesis regarding the putative seizure onset zone (SOZ) and propagation. This article covers the technical and theoretical aspects of SEEG, including the surgical techniques and precautions, hypothesis construction, and the interpretation of the recording, all with the aim of providing an introductory guide to SEEG.

Stereotactic EEG Practices: A Survey of United States Tertiary Referral Epilepsy Centers

PURPOSE

Stereotactic EEG (SEEG) is being increasingly used in the intracranial evaluation of refractory epilepsy in the United States. In this study, the authors describe current practice of SEEG among National Association of Epilepsy Centers tertiary referral (level IV) centers.

METHODS

Using the Survey Monkey platform, a survey was sent to all National Association of Epilepsy Centers level IV center directors.

RESULTS

Of 192 centers polled, 104 directors completed the survey (54% response rate). Ninety-two percent currently perform SEEG. Of these, 55% of institutions reported that greater than 75% of their invasive electrode cases used SEEG. Stereotactic EEG was commonly used over subdural electrodes in cases of suspected mesial temporal lobe epilepsy (87%), nonlesional frontal lobe epilepsy (79%), insular epilepsy (100%), and individuals with prior epilepsy surgery (74%). Most centers (72%) used single-lead electrocardiogram monitoring concurrently with SEEG, but less than half used continuous pulse oximetry (47%) and only a few used respiratory belts (3%). Other significant intercenter technical variabilities included electrode nomenclature and choice of reference electrode. Patient care protocols varied among centers in patient-to-nurse ratio and allowed patient activity. Half of all centers had personnel who had prior experience in SEEG (50.5%); 20% of centers had adopted SEEG without any formal training.

CONCLUSIONS

Stereotactic EEG has become the principal method for intracranial EEG monitoring in the majority of epilepsy surgery centers in the United States. Most report similar indications for use of SEEG, though significant variability exists in the utilization of concurrent cardiopulmonary monitoring as well as several technical and patient care practices. There is significant variability in level of background training in SEEG among practitioners. The study highlights the need for consensus statements and guidelines to benchmark SEEG practice and develop uniform standards in the United States.

Surgical Robot-Enhanced Implantation of Intracranial Depth Electrodes for Single Neuron Recording Studies in Patients with Medically Refractory Epilepsy: A Technical Note

OBJECTIVE

Single neuron or unit recording enables researchers to measure the electrophysiologic responses of single neurons using a microelectrode system. This approach is widely used in cognitive science and has become more widespread in humans with the use of hybrid (micro-within-macrowire) depth electrodes that enable the implantation of microwires into the brain parenchyma.

METHODS

The authors describe their surgical technique in a total of 7 patients with intractable epilepsy who underwent robot-enhanced stereoencephalography in which both standard (nonhybrid) and hybrid depth electrodes were used for invasive chronic monitoring.

RESULTS

The technique and accuracy of the procedure were evaluated with a total of 84 depth electrodes (46 hybrid, 38 standard) in 7 patients. No major complications, such as intracranial hemorrhage, infection or cerebrospinal fluid leakage, occurred regardless of the type of electrode used.

CONCLUSIONS

The addition of hybrid depth electrodes for the purpose of in vivo single neuron recording in robot-enhanced stereoencephalography procedures is safe and does not impact the accuracy of targeting or patient safety.

Transient hypoxemia induced by cortical electrical stimulation: A mapping study in 75 patients

OBJECTIVE

To identify which cortical regions are associated with direct electrical stimulation (DES)-induced alteration of breathing significant enough to impair pulse oximetry (SpO₂).

METHODS

Evolution of SpO₂ after 1,352 DES was analyzed in 75 patients with refractory focal epilepsy who underwent stereo-EEG recordings. For each DES, we assessed the change in SpO₂ from 30 seconds prior to DES onset to 120 seconds following the end of the DES. The primary outcome was occurrence of stimulation-induced transient hypoxemia as defined by decrease of SpO₂ ≥5% within 60 seconds after stimulation onset as compared to pre-DES SpO₂ or SpO₂ nadir <90% during at least 5 seconds. Localization of the stimulated contacts was defined according to MarsAtlas brain parcellation and Freesurfer segmentation.

RESULTS

A stimulation-induced transient hypoxemia was observed after 16 DES (1.2%) in 10 patients (13%), including 6 in whom SpO₂ nadir was <90%. Among these 16 DES, 7 (44%) were localized within the perisylvian cortex. After correction for individual effects and the varying number of DES contributed by each person, significant decrease of SpO₂ was significantly associated with the localization of DES (p = 0.019).

CONCLUSION

Though rare, a significant decrease of SpO₂ could be elicited by cortical direct electrical stimulation outside the temporo-limbic structures, most commonly after stimulation of the perisylvian cortex.

Practice of stereoelectroencephalography (sEEG) in drug-resistant epilepsy: Retrospective series with surgery and thermocoagulation outcomes

OBJECTIVE

The aim of this study was to determine the success rate of sEEG in locating the epileptogenic zone (EZ) in patients with pharmaco-resistant epilepsy. Secondary objectives were to analyze sEEG-related morbidity and outcomes for post-sEEG thermocoagulation and cortical resection.

METHODS

Data were collected on 49 sEEGs from 46 consecutive patients between 2010 and 2018. Following sEEG, either resective or palliative surgery with vagus nerve stimulation was performed. In 8 patients, EZ thermocoagulation was performed before EEG leads were withdrawn. Outcomes were collected based on the Engel and ILAE outcome scales.

RESULTS

sEEG was contributive in 45 of 49 recordings, with a success rate of 92% in locating the EZ. Minor complications, such as transient neurologic deficit and electrode implantation failures, occurred in 6%. One major complication occurred, with death due to atypical late hematoma. Thermocoagulation was performed in 8 patients and stopped or significantly reduced seizure frequency in 7 (88%). Outcome of surgical resection (n=33) was good, with 20 (61%) seizure-free patients and 32 (97%) with definite improvement.

CONCLUSIONS

Our findings suggest that sEEG is an effective technique for EZ location in patients with drug-resistant epilepsy. sEEG was contributive in up to 92% of patients, allowing thermocoagulation and/or surgical resection that resulted in seizure-freedom in two-thirds and seizure-reduction in one-third of cases. This study highlights the need for strict selection of implantation candidates, with strong initial hypothesis as to EZ location.