Diagnostic utility of bilateral stereoelectroencephalography sampling in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of medically refractory epilepsy in adults. While patients with concordant noninvasive findings and hippocampal sclerosis (HS) might proceed directly to surgery, those with discordant data, suspected bilateral involvement, or atypical presentation often require stereoelectroencephalography (SEEG). The diagnostic and therapeutic implications of bilateral temporal sampling remain uncertain. The aim of this study was to evaluate the yield and clinical impact of bilateral SEEG in TLE.

The authors retrospectively reviewed data collected from patients with medically refractory epilepsy who underwent bilateral SEEG at a single institution from March 2017 and June 2025. Inclusion criteria were a pre-SEEG hypothesis of temporal onset, nonlesional or mesial TLE, with or without HS, and bilateral hippocampal/amygdala sampling. Patients were grouped as concordant, discordant, or bilateral based on pre-SEEG noninvasive data. The diagnostic yield, number of SEEG studies required to alter 1 patient's initial hypothesis, and seizure outcomes were analyzed.

Of 197 patients who underwent SEEG, 54 met inclusion criteria. Pre-SEEG hypotheses were concordant in 20 patients, discordant in 8 patients, and bilateral in 26 patients. SEEG revealed contralateral or bilateral seizure onset in 35% of concordant cases and confirmed unilateral onset in 46% of presumed bilateral cases. Overall, 21% of presumed unilateral TLE showed bilateral involvement. The number needed to treat was 2.9 for the concordant group and 2.2 for the bilateral group. Following SEEG, 38 patients underwent resection, laser ablation, or neuromodulation. At the last follow-up, 49% of patients achieved Engel class I or II outcomes, with best results for those with resection/ablation (79% Engel class I or II).

Bilateral SEEG provides clinically meaningful information in both unilateral and bilateral TLE, uncovering contralateral involvement in presumed unilateral cases and confirming unilateral foci in nearly half of presumed bilateral cases. Although SEEG is not necessary for all patients with TLE-HS and concordant studies, when it is indicated, bilateral sampling might be important to avoid misclassification and guide resective/ablative versus neuromodulatory treatment planning.