Thalamic stereo-electroencephalography exploration in pediatric drug-resistant epilepsy: implantation technique and complications.

Objective: Patients with drug-resistant epilepsy (DRE) are often referred for phase II evaluation with stereo-electroencephalography (SEEG) to identify a seizure onset zone for guiding definitive treatment. For patients without a focal seizure onset zone, neuromodulation targeting the thalamic nuclei-specifically the centromedian nucleus, anterior nucleus of the thalamus, and pulvinar nucleus-may be considered. Currently, thalamic nuclei selection is based mainly on the location of seizure onset, without a detailed evaluation of their network involvement. This study aimed to prospectively assess the involvement of thalamic nuclei in seizure propagation during the SEEG evaluation in pediatric patients with DRE.

Methods: This prospective study investigated the placement of thalamic electrodes during the SEEG phase II evaluation in pediatric patients. Following a phase I presurgical evaluation, patients were presented at a comprehensive epilepsy conference, where recommendations for SEEG evaluation were made. In cases in which neuromodulation was a potential outcome, thalamic nuclei were prospectively selected in 10 patients based on a preimplantation hypothesis. During the SEEG evaluation, electrical activity recorded from the thalamic electrodes was analyzed. If the patient went on to undergo neuromodulation, the recorded data guided the thalamic target selection.

Results: Ten patients underwent implantation of 14 thalamic electrodes during SEEG implantation. No surgical complications were associated with either the placement or removal of these electrodes. Video-EEG analysis performed during the interictal period was unremarkable in 4 patients and revealed network spikes in 6 patients. These networks describe brain regions that may be connected structurally and functionally. Electrographic seizure onsets in thalamic contacts were simultaneous with cortical onset in 3 patients, early in 5, late in 1, and not involved in 1 patient. Seventy-two of the 109 seizures (66%) captured during SEEG involved thalamic contacts. Seven patients underwent neuromodulation after SEEG revealed an extensive network, rather than a focal onset, which precluded focal surgical resection. In all 7 of these patients, thalamic SEEG results were instrumental in guiding final neuromodulation targets chosen for implantation.

Conclusions: In pediatric patients without a single resectable focus as a cause of their DRE, thalamic implantation during phase II SEEG evaluation is both safe and effective for assessing thalamic nuclear network involvement. This information could be instrumental in selecting thalamic nuclei for neuromodulation, allowing for a more individualized approach to treatment.