Abstracts

Rationale: Despite the relatively higher rate of frontal lobe epilepsy (FLE) in children, few studies have been conducted in pediatric FLE compared to temporal lobe epilepsy. Our hypothesis was that spread of seizure activity outside the frontal lobe due to cortico-cortical connections resulted in alteration in the cortex beyond the frontal lobe in children with intractable FLE. The aim of this study was to identify regions of reduced cortical thickness, surface area and cortical volume beyond the frontal lobe in children with intractable FLE. Methods: The study has the approval of the institutional research ethics board. Seventeen children with frontal lobe epilepsy, consisting of 10 females and 7 males, mean age of 11.7 years, who were being evaluated for epilepsy surgery were recruited. Twelve children had left FLE and five children had right FLE. Twenty-six age-matched healthy controls, consisting of 12 females and 14 males, mean age of 11.5 years, were recruited. Volumetric T1-weighted imaging was performed on both patients and controls. The volumetric T1 images of all patients with right FLE were side-flipped so that the seizure focus was on the left side in all patients. Cortical thickness, surface area and volume were measured using FreeSurfer and compared between patients and controls. Regions that demonstrated significant cortical thinning were regressed against age of seizure onset, duration of epilepsy, seizure frequency and number of medications. Results: Significant cortical thinning in the hemisphere ipsilateral to the seizure focus included the superior frontal, paracentral, cingulum, precentral, postcentral, supramarginal, inferior parietal and superior temporal gyri and contralateral to the seizure focus included the superior and middle frontal, precentral, supramarginal, superior parietal and superior temporal gyri (p?0.004 in all regions). Regions that showed reduced cortical surface area and volume were similar to those regions that demonstrated cortical thinning, but were less widespread. Age at seizure onset (p=0.003) and frequency of seizures (p=0.002) predicted cortical thinning of the superior frontal gyrus ipsilateral to seizure focus. Duration of epilepsy was a weaker predictor of cortical thinning in the superior frontal (p=0.026) and inferior parietal (p=0.019) gyri ipsilateral to seizure focus. There was no significant association between the number of medications and cortical thinning in the hemisphere ipsilateral to seizure focus (p>0.01). There were also no significant associations between age at seizure onset, duration of epilepsy, frequency of seizures or number of medications and cortical thinning in the contralateral hemisphere (p>0.01). Conclusions: Widespread cortical changes in children with intractable FLE suggested that spread of epileptogenic focus could lead to widespread injury to the cortex. The strong association between cortical thinning and age of seizure onset as well as seizure frequency indicates that the developing brain is more prone to seizure-induced injury and that this injury is more pronounced with increasing severity of seizures.