Changing concepts in presurgical assessment for epilepsy surgery

Electrical Cortical Stimulation: Mapping for Function and Seizures

Surgical procedures for the treatment of epilepsy and brain tumors can involve resection of regions closed or merged to functionally eloquent cortical areas. Removal of language, primary motor, or sensory areas can be associated with transient or permanent functional deficits, which should be avoided if possible. Functional electrical cortical stimulation is a reliable technique to prevent or minimize motor, sensory and language deficits and has been used in humans since the 1950s to identify functional cortex, and it can also localize epileptogenic regions. This article discusses functional electrical stimulation in adults and children for different functional modalities.

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 In 8 patients, EZ thermocoagulation was performed before EEG leads were withdrawn.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.

Network Changes after Epilepsy Surgery: It's Time to Reconnect

Network-Targeted Approach and Postoperative Resting-State Functional Magnetic Resonance Imaging Are Associated With Seizure Outcome

Boerwinkle VL, Cediel EG, Mirea L, et al. Ann Neurol. 2019;86(3):344-356.

Objective:

Postoperative resting-state functional magnetic resonance imaging (MRI) in children with intractable epilepsy has not been quantified in relation to seizure outcome. Therefore, its value as a biomarker for epileptogenic pathology is not well understood.

Methods:

In a sample of children with intractable epilepsy who underwent prospective resting-state seizure onset zone (SOZ)-targeted epilepsy surgery, postoperative resting-state functional MRI (rs-fMRI) was performed 6 to 12 months later. Graded normalization of the postoperative resting-state SOZ was compared to seizure outcomes, patient, surgery, and anatomical MRI characteristics.

Results:

A total of 64 cases were evaluated. Network-targeted surgery, followed by postoperative rs-fMRI normalization was significantly (P < .001) correlated with seizure reduction, with a Spearman rank correlation coefficient of 0.83. Of 39 cases with postoperative rs-fMRI SOZ normalization, 38 (97%) became completely seizure free. In contrast, of the 25 cases without complete rs-fMRI SOZ normalization, only 3 (5%) became seizure free. The accuracy of rs-fMRI as a biomarker predicting seizure freedom is 94%, with 96% sensitivity and 93% specificity.

Interpretation:

Among seizure localization techniques in pediatric epilepsy, network-targeted surgery, followed by postoperative rs-fMRI normalization, has high correlation with seizure freedom. This study shows that rs-fMRI SOZ can be used as a biomarker for the epileptogenic zone, and postoperative rs-fMRI normalization is a biomarker for SOZ quiescence.