Abstracts

Rationale: Stereotactic electroencephalography (sEEG) affords the opportunity for three-dimensional sampling of candidate epileptogenic zones. The aim of this study was to examine the diagnostic yield of sEEG in patients with drug-resistant epilepsy and bilateral epileptogenic lesions on imaging. Methods: Records of 81 consecutive patients who underwent sEEG implantation at our institution from January 2016 - May 2019 were reviewed to identify patients with bilateral MRI lesions that were considered to be potentially epileptogenic. Pre- and post-implantation data including intellectual function, seizure semiology, focality of interictal and ictal scalp EEG, imaging and source localization results, implantation strategy, and sEEG implant duration were collected. Outcomes of interest were rates of progression to focal resection, seizure freedom after resection, and whether the pre-implantation hypothesis was correct. Pre-implantation data were compared to outcomes via Fisher's exact test for a relationship. Results: Thirteen patients (8 female, aged 8-67) with bilateral, potentially epileptogenic MRI findings were identified. None of the patients had serious adverse effects to sEEG. Seven (54%) proceeded to focal resection, of whom six (86%) achieved seizure-freedom for mean follow-up of 7 months (range 2-12). Pre-implantation hypothesis was correct in those seven plus an additional patient with independent bilateral seizure onset (62%). Resection was not recommended in patients with diffuse or multifocal seizure onset. Resection was more likely in patients with localizing semiology than in those without (2/2 versus 5/11, p=0.46), and in those implanted with fewer than 14 electrodes than in those with more electrodes (5/7 vs 2/6, p=0.29). The hypothesis was more likely to be correct in patients with a seizure semiology that was localizing and lateralizing than those without (2/2 vs 5/11, p=0.46), and in patients with single seizure focus on scalp EEG than in those without (5/10 vs 0/3, p=0.23). Conclusions: Stereotactic EEG can safely identify solitary seizure-onset zones in patients with bilateral potentially epileptogenic lesions. Seizure freedom rates are high in these patients who undergo subsequent resection. There was a trend to suggest that localizing semiology, implantation strategy comprising fewer sEEG electrodes, and the presence of a single focus on scalp EEG may increase the odds of correct pre-implantation hypothesis and subsequent resection; however, these associations did not reach statistical significance due to small numbers. Funding: No funding