Non-lesional epilepsy does not necessarily convey poor outcomes after invasive monitoring followed by resection or thermal ablation.

Objective: We aimed to compare outcomes including seizure-free status at the last follow-up in adult patients with medically refractory focal epilepsy identified as lesional vs. non-lesional based on their magnetic resonance imaging (MRI) findings who underwent invasive evaluation followed by subsequent resection or thermal ablation (LiTT).

Methods: We identified 88 adult patients who underwent intracranial monitoring between 2014 and 2021. Of those, 40 received resection or LiTT, and they were dichotomized based on MRI findings, as lesional ( = 28) and non-lesional ( = 12). Patient demographics, seizure characteristics, non-invasive interventions, intracranial monitoring, and surgical variables were compared between the groups. Postsurgical seizure outcome at the last follow-up was rated according to the Engel classification, and postoperative seizure freedom was determined by Kaplan-Meyer survival analysis. Statistical analyses employed Fisher's exact test to compare categorical variables, while a t-test was used for continuous variables.

Results: There were no differences in baseline characteristics between groups except for more often noted PET abnormality in the lesional group ( = 0.0003). 64% of the lesional group and 57% of the non-lesional group received surgical resection or LiTT ( = 0.78). At the last follow-up, 78.5% of the patients with lesional MRI findings achieved Engel I outcomes compared to 66.7% of non-lesional patients ( = 0.45). Kaplan-Meier curves did not show a significant difference in seizure-free duration between both groups after surgical intervention ( = 0.49).

Significance: In our sample, the absence of lesion on brain MRI was not associated with worse seizure outcomes in adult patients who underwent invasive intracranial monitoring followed by resection or thermal ablation.