Long-Term Outcomes of Nonlesional Extratemporal Epilepsy Surgery Using Subdural Grid Implantation

Nonlesional extratemporal lobe epilepsy (ETE) remains one of the most challenging forms of drug-resistant epilepsy to treat surgically because seizure onset zones are often poorly defined on conventional neuroimaging. The long-term effectiveness of subdural grid-guided surgery in this population remains incompletely understood. This study aimed to evaluate long-term surgical outcomes in patients with intractable nonlesional extratemporal epilepsy who underwent subdural grid-guided epilepsy surgery. A retrospective study was conducted from January 1, 2014 to December 31, 2024. Clinical, pathological, and invasive electroencephalography data were reviewed. Seizure outcomes were assessed using Engel's classification at 6 months and 2 years after surgery. Fifty-five patients with nonlesional extratemporal epilepsy were included. Seizure freedom (Engel class I) was achieved in 12 patients (21.8%) at 6 months and increased to 30 patients (54.5%) at 2 years. These improvements were not statistically significant (p = 0.16 and 0.53, respectively). Favorable trends toward better seizure outcomes were observed in patients aged from adolescence to middle adulthood, those with tumor pathology, and those with parietal lobe seizure foci. Subdural grid-guided surgery for nonlesional extratemporal epilepsy resulted in seizure-free rates of 21.8% at 6 months and 54.5% at 2 years, with improvement over time but without statistically significant predictors of outcome.