Use of Stereotactic EEG Investigation in Patients Who Are Hemispherectomy Candidates

Introduction: Hemispherectomy is an important surgical technique for seizure control. Its efficacy is necessarily coupled with the loss of residual functions of the disconnected hemisphere, hence patient selection is of paramount importance.

Methods: In a 3 ½-year period between 2019 to 2023, 65 sEEG and 11 functional hemispherectomy surgeries were carried out in the authors’ institution. All of the patients have had at least a one-year follow up. Four patients who fulfilled the standard criteria for hemispherectomy underwent sEEG investigation. All four patients also underwent vEEG, MRI, functional MRI, PET, and neuropsychological studies. One patient underwent a MEG study.

Results: Patients’ age ranged from 10 to 16 years, and epilepsy etiologies were related to neonatal middle cerebral artery (MCA) stroke secondary to prematurity (n=2), abusive head trauma (n=1), and unknown etiology (n=1). Two cases involved the left hemisphere. All patients presented with various degrees of hemiparesis with corresponding cerebral hemisphere and ipsilateral midbrain atrophy. Functional MRI determined language dominance in one patient; another patient's language dominance was indeterminate; two patients failed to complete functional MRI. vEEG showed fast, diffuse hemispheric involvement and hinted at seizure onset zone (SOZ) in central and frontal regions, a diffuse midline location, and posterior quadrant. vEEG findings were the main indications for sEEG investigation. During intracranial recording, sEEG electrodes were used for functional mapping. Based on results, patients underwent posterior quadrant disconnection (n=1), posterior quadrant disconnection + posterior insula resection (n=1) , DLPFC resection (n=1) , and DMPFC + orbitofrontal resection (n=1). All 4 patients were seizure-free at one year follow-up with documented functional improvement. All patients remained without focal neurologic deficit.

Conclusion : In patients with large MCA stroke, determining the degree of residual function in the affected hemisphere and SOZ can be difficult. sEEG can be used to guide a targeted surgical approach instead of hemispherectomy.