Long-term seizure outcomes after pediatric temporal lobectomy: does brain MRI lesion matter?

User-defined virtual sensors: A new solution to the problem of temporal plus epilepsy sources

OBJECTIVE

The most common medically resistant epilepsy (MRE) involves the temporal lobe (TLE), and children designated as temporal plus epilepsy (TLE+) have a five-times increased risk of postoperative surgical failure. This retrospective, blinded, cross-sectional study aimed to correlate visual and computational analyses of magnetoencephalography (MEG) virtual sensor waveforms with surgical outcome and epilepsy classification (TLE and TLE+).

METHODS

Patients with MRE who underwent MEG and iEEG monitoring and had at least 1 year of postsurgical follow-up were included in this retrospective analysis. User-defined virtual sensor (UDvs) beamforming was completed with virtual sensors placed manually and symmetrically in the bilateral amygdalohippocampi, inferior/middle/superior temporal gyri, insula, suprasylvian operculum, orbitofrontal cortex, and temporoparieto-occipital junction. Additionally, MEG effective connectivity was computed and quantified using eigenvector centrality (EC) to identify hub regions. More conventional MEG methods (equivalent current dipole [ECD], standardized low-resolution brain electromagnetic tomography, synthetic aperture magnetometry beamformer), UDvs beamformer, and EC hubs were compared to iEEG.

RESULTS

Eighty patients (38 female, 42 male) with MRE (mean age = 11.3 ± 6.2 years, range = 1.0-31.5) were identified and included. Twenty-five patients (31.3%) were classified as TLE, whereas 55 (68.8%) were TLE+. When modeling the association between MEG method, iEEG, and postoperative surgical outcome (odds of a worse [International League Against Epilepsy (ILAE) class > 2] outcome), a significant result was seen only for UDvs beamformer (odds ratio [OR] = 1.22, 95% confidence interval [CI] = 1.01-1.48). Likewise, when the relationship between MEG method, iEEG, and classification (TLE and TLE+) was modeled, only UDvs beamformer had a significant association (OR = 1.47, 95% CI = 1.13-1.92). When modeling the association between EC hub location and resection/ablation to postoperative surgical outcome (odds of a good [ILAE 1-2] outcome), a significant association was seen (OR = 1.22, 95% CI = 1.05-1.43).

SIGNIFICANCE

This study demonstrates a concordance between UDvs beamforming and iEEG that is related to both postsurgical seizure outcome and presurgical classification of epilepsy (TLE and TLE+). UDvs beamforming could be a complementary approach to the well-established ECD, improving invasive electrode and surgical resection planning for patients undergoing epilepsy surgery evaluations and treatments.

Challenging Cortical Explorations in Difficult-to-Localize Seizures: The Rationale and Usefulness of Perisylvian Paralimbic Explorations With Orthogonal Stereoelectroencephalography Depth Electrodes

BACKGROUND AND OBJECTIVE

Stereoelectroencephalography (SEEG) is an invasive monitoring method designed to define and localize the epileptogenic zone (EZ) and explore the putative network responsible for the electroclinical seizures using anatomo-functional-electroclinical correlations. When indicated by semiology in selected patients, exploration of both limbic and paralimbic (PL) regions is indispensable. However, the PL cortex is located in deep and highly vascularized areas in proximity to the anterior Sylvian fissure and middle cerebral artery branches. Thus, those explorations are considered surgically challenging because of the multilobar location and fear of hemorrhagic events. Here, we discuss and illustrate the rationale and SEEG methodology approach in usefulness of exploring the PL regions using standard orthogonal SEEG depth electrode trajectories with the Talariach reference system.

METHODS

We retrospectively studied PL exploration from a cohort of 71 consecutive SEEG procedures from Nov 2019 to Nov 2022 and identified 31 patients who underwent PL trajectories.

RESULTS

In 31 patients, there were 32 SEEG trajectories, and no major complications were observed. PL electrodes were consistently implanted in the C10/D10 coordinates of the Talariach reference coordinates. The most common confirmed EZ in our cohort was mesio-temporal (45%), followed by temporo-perisylvian regions (16%), ventromedial frontal (13%), and mesio-lateral temporal regions (13%). The PL contacts were involved in the EZ in 10 patients (32%). Of 31 patients, 25 underwent resective surgery, and 19 obtained Engel 1 outcome with a mean follow-up of 25 months (range 12-41 months) after surgery.

CONCLUSION

The orthogonal perisylvian PL trajectories are feasible and useful in sampling multiple PL regions with single-electrode trajectories. In patients with perisylvian seizures, sampling PL structures may contribute to an improved understanding of seizure propagation and the optimal anatomic demarcation of the EZs in this surgically challenging region.

PET/MRI Applications in Pediatric Epilepsy

Epilepsy neuroimaging assessment requires exceptional anatomic detail, physiologic and metabolic information. Magnetic resonance (MR) protocols are often time-consuming necessitating sedation and positron emission tomography (PET)/computed tomography (CT) comes with a significant radiation dose. Hybrid PET/MRI protocols allow for exquisite assessment of brain anatomy and structural abnormalities, in addition to metabolic information in a single, convenient imaging session, which limits radiation dose, sedation time, and sedation events. Brain PET/MRI has proven especially useful for accurate localization of epileptogenic zones in pediatric seizure cases, providing critical additional information and guiding surgical decision making in medically refractory cases. Accurate localization of seizure focus is necessary to limit the extent of the surgical resection, preserve healthy brain tissue, and achieve seizure control. This review provides a systematic overview with illustrative examples demonstrating the applications and diagnostic utility of PET/MRI in pediatric epilepsy.

Brain Surgery for Medically Intractable Epilepsy

This review covers the broad topic of brain surgery in the treatment of pediatric intractable epilepsy. The authors review the latest advancements in the presurgical workup as well as the mandatory tests needed to explore the epilepsy workup in these children. They describe the different types of epilepsy from a surgical standpoint (temporal, extratemporal, multifocal, and hemispheric epilepsies) and various surgical procedures that can be proposed depending on the clinical scenario: lesionectomies, lobectomies, hemispherectomies, neuromodulation, and palliative surgeries. They also describe the key differences of the pediatric patient as compared with the adult patient in such pathologic conditions.

Intrinsic Thalamic Network in Temporal Lobe Epilepsy With Hippocampal Sclerosis According to Surgical Outcomes

Background: The aim of this study was to identify the differences of intrinsic amygdala, hippocampal, or thalamic networks according to surgical outcomes in temporal lobe epilepsy (TLE) patients with hippocampal sclerosis (HS).

Methods: We enrolled 69 pathologically confirmed TLE patients with HS. All patients had pre-operative three-dimensional T1-weighted MRI using a 3.0 T scanner. We obtained the structural volumes of the amygdala nuclei, hippocampal subfields, and thalamic nuclei. Then, we investigated the intrinsic networks based on volumes of these structures using structural covariance and graph theoretical analysis.

Results: Of the 69 TLE patients with HS, 21 patients (42.1%) had poor surgical outcomes, whereas 40 patients (57.9%) had good surgical outcomes. The volumes in the amygdala nuclei, hippocampal subfields, and thalamic nuclei were not different according to surgical outcome. In addition, the intrinsic amygdala and hippocampal networks were not different between the patients with poor and good surgical outcomes. However, there was a significant difference in the intrinsic thalamic network in the ipsilateral hemisphere between them. The eccentricity and small-worldness index were significantly increased, whereas the characteristic path length was decreased in the patients with poor surgical outcomes compared to those with good surgical outcomes.

Conclusion: We successfully demonstrated significant differences in the intrinsic thalamic network in the ipsilateral hemisphere between TLE patients with HS with poor and good surgical outcomes. This result suggests that the pre-operative intrinsic thalamic network can be related with surgical outcomes in TLE patients with HS.

Subtraction ictal SPECT co-registered to MRI (SISCOM) patterns in children with temporal lobe epilepsy

OBJECTIVE

We evaluated SISCOM patterns and their relationship with surgical outcome in children with temporal lobe epilepsy (TLE) who had undergone a temporal lobe surgery.

METHODS

This was an observational study evaluating SISCOM patterns in 40 children with TLE. We classified SISCOM patterns into 4 categories; (i) unilateral anteromesial and/or anterolateral temporal pattern; (ii) unilateral anteromesial and/or anterolateral temporal plus posterior extension pattern; (iii) bilateral anteromesial and/or anterolateral temporal pattern; and (iv) atypical pattern. Determinants of SISCOM pattern and correlation between postoperative outcomes and SISCOM patterns were evaluated.

RESULTS

Pattern (i), (ii), (iii), and (iv) were identified in 10 (25%), 14 (35%), 0 (0%), and 16 (40%) patients, respectively. There was no significant correlation between patterns and postoperative outcomes. SISCOM patterns significantly associated with the presence of hippocampal sclerosis and type of focal cortical dysplasia (p-value = 0.048 and 0.036, respectively). Patients with HS had 5 times the odds of having unilateral temporal pattern, compared to patients with other neuropathology (OR = 5, 95% CI 0.92 to 27.08). Patients with FCD type 2 had 9.71 times the odds of having atypical pattern, compared to patients with other types of FCD (OR = 9.71, 95% CI 0.92 to 103.04). Lobar concordance of SISCOM and ictal and interictal scalp EEG significantly correlated with postoperative outcomes (p-value = 0.018 and 0.013, respectively).

CONCLUSION

Three SISCOM patterns were seen. Patients with HS had increased odds of having unilateral temporal pattern while patients with FCD type 2 had increased odds of having atypical pattern. However, there was no significant correlation between SISCOM patterns and postoperative outcomes. Lobar concordance of SISCOM and ictal and interictal scalp EEG significantly correlated with postoperative outcome.

SIGNIFICANCE

This study shows that the distribution of SISCOM patterns and their relationship with postoperative outcomes in children with TLE are different from adult population. Besides, SISCOM may add only limited diagnostic and prognostic information in children with drug-resistant TLE undergoing epilepsy surgery. Further evaluation to identify patient populations that may benefit from SISCOM is desirable.

Fast Automated Stereo-EEG Electrode Contact Identification and Labeling Ensemble

INTRODUCTION

Stereotactic electroencephalography (SEEG) has emerged as the preferred modality for intracranial monitoring in drug-resistant epilepsy (DRE) patients being evaluated for neurosurgery. After implantation of SEEG electrodes, it is important to determine the neuroanatomic locations of electrode contacts (ECs), to localize ictal onset and propagation, and integrate functional information to facilitate surgical decisions. Although there are tools for coregistration of preoperative MRI and postoperative CT scans, identification, sorting, and labeling of SEEG ECs is often performed manually, which is resource intensive. We report development and validation of a software named Fast Automated SEEG Electrode Contact Identification and Labeling Ensemble (FASCILE).

METHODS

FASCILE is written in Python 3.8.3 and employs a novel automated method for identifying ECs, assigning them to respected SEEG electrodes, and labeling. We compared FASCILE with our clinical process of identifying, sorting, and labeling ECs, by computing localization error in anteroposterior, superoinferior, and lateral dimensions. We also measured mean Euclidean distances between ECs identified by FASCILE and the clinical method. We compared time taken for EC identification, sorting, and labeling for the software developer using FASCILE, a first-time clinical user using FASCILE, and the conventional clinical process.

RESULTS

Validation in 35 consecutive DRE patients showed a mean overall localization error of 0.73 ± 0.15 mm. FASCILE required 10.7 ± 5.5 min/patient for identifying, sorting, and labeling ECs by a first-time clinical user, compared to 3.3 ± 0.7 h/patient required for the conventional clinical process.

CONCLUSION

Given the accuracy, speed, and ease of use, we expect FASCILE to be used frequently for SEEG-driven epilepsy surgery. It is freely available for noncommercial use. FASCILE is specifically designed to expedite localization of ECs, assigning them to respective SEEG electrodes (sorting), and labeling them and not for coregistration of CT and MRI data as there are commercial software available for this purpose.