Cortical thickness asymmetries and surgical outcome in neocortical epilepsy

Abstract

Purpose: We evaluated if cortical thickness measures were associated with surgical outcome in patients with non-lesional neocortical epilepsy.

Methods: Twenty-one young patients (age: 2.4-19.7years) with epilepsy of neocortical origin and normal MRI underwent two-stage epilepsy surgery with subdural EEG monitoring. Cortical thickness was measured on presurgical volumetric MRI using the FreeSurfer software. The prognostic value of hemispheric and lobar/regional cortical thickness measures for 1-year and 2-year post-surgical seizure outcome has been analyzed.

Results: At one-year follow-up, 14 patients (67%) were seizure-free. Hemispheric and frontal lobe cortical thickness showed no/minimal asymmetry in seizure-free patients but thinner cortex ipsilateral to the seizure focus in those with recurrent seizures (p=0.02). More robust differences were found in patients≥6years of age (p=0.006 for frontal asymmetries), whose cortical thickness asymmetries remained prognostic for 2-year post-surgical outcome (p=0.007). By using an optimal cutoff threshold based on a receiver operating characteristic analysis, mean hemispheric asymmetry predicted one-year seizure freedom with 93% sensitivity and 71% specificity in the whole group, and with 100% sensitivity and 92% specificity in patients≥6years of age.

Conclusion: In patients with neocortical epilepsy and normal MRI, neocortical thinning in the epileptic hemisphere, particularly in frontal cortex, is associated with poor surgical outcome. Although these results require validation in a larger cohort prospectively, these data suggest that presurgical evaluation of cortical thickness may assist in identification of patients at high risk for surgical failure.

Keywords: Cortical thickness; Epilepsy; Epilepsy surgery; Frontal lobe; MRI; Surgical outcome.