Cortical thickness asymmetries and surgical outcome in neocortical epilepsy

• Decreased ipsilateral cortical thickness predicts post-operative seizures.
• Cortical thickness asymmetries may predict seizure-free outcome with around 90% accuracy when using an optimized threshold.
• Cortical thickness asymmetries in the frontal lobe have the strongest prognostic value.

PurposeWe evaluated if cortical thickness measures were associated with surgical outcome in patients with non-lesional neocortical epilepsy.MethodsTwenty-one young patients (age: 2.4–19.7 years) 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.ResultsAt 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 ≥ 6 years 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 ≥ 6 years of age.ConclusionIn 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.