Abstracts

Rationale: The epileptogenic zone (EZ) can be defined as the cortical and subcortical areas responsible for the generation and primary organization of the epileptic activity. The belief exists among some groups that in order to maximize their patients’ chances of becoming seizure free, they should resect as much tissue as is deemed possible without causing major post-operative neurological deficits. A greater understanding of the relationship between resection volume and seizure outcomes is needed.Methods: The post-operative volumetric magnetic resonance images, surgical data, and seizure outcomes were retrospectively gathered from a cohort of 44 consecutive patients with medically refractory focal frontal lobe epilepsy who underwent SEEG guided frontal lobe resection. The volumes of the resection cavities were digitally calculated. The borders of the resection cavity were manually defined by three researchers and the enclosed volume was thereby calculated via a semi-automatic voxel based segmentation method. The cohort was divided into two groups based on the presence of post-operative seizure recurrence or post-operative seizure freedom. The median volumes of resection between the two groups was compared using the Wilcoxon rank-sum test. In addition, data related to gender, age, type of resection, side of resection, MRI results and surgical pathology results were analyzed. Furthermore, a ROC curve was used to identify the threshold for resection that best predicts post-operative seizure recurrence. The mean follow-up period was 13 months.Results: No significant difference was found between the median volumes of the two cohorts (p = 0.55). Furthermore, the threshold with the best predictive value for post-operative seizure recurrence was found to be ≤ 40.55 cm3 (sensitivity = 0.5, specificity = 0.72). There was some evidence that patients with CD pathology and those with lobar resections were at lower risk of recurrence, but neither reached statistical significance (both p < 0.20).Conclusions: The volume of resection is a poor predictor of seizure recurrence following frontal lobe resection. Within this cohort, no reliable threshold exists for resection volume, above or below which a patient is more or less likely to achieve freedom from seizures. Neither larger nor smaller resections necessarily lead to increased or decreased chance of seizure freedom, respectively.