Abstracts

Rationale: The corpus callosum (CC) is the largest commissural pathway in the human brain and as such is also the most important inter-hemispheric propagation pathway for epileptic activity. The fibers of the CC are known to connect homologous cortical areas. This study aimed to investigate whether children with medically intractable neocortical epilepsy have topological microstructural changes involving CC, using pre-surgical diffusion tensor imaging (DTI) sequences. Methods: Thirty-three patients with medically intractable neocortical epilepsy had epilepsy surgery at the Children s Hospital of Alabama. The mean age at surgery was 9.8years (1 year 11 months-18 year 2 months). Twenty-five (75.8%) were right-handed. Only sixteen (48.53 %) had visible lesions on 1.5 Tesla pre-operative brain MRI. Most patients (32/33) underwent intracranial EEG monitoring prior to surgery. Seventeen had seizure onset localized to the frontal lobe while the rest had in parietal, temporal, or temporo-occipital seizure onset zones. Twenty-seven patients (81.8%) have favorable outcomes (Engel class I-18, II-9). The pathology was FCD in all cases. Twenty-eight, age-matched healthy controls were compared. The regions of interest (ROIs) were outlined at each Witelson region (WR). Fractional anisotropy (FA) was determined in each WR. We performed tractography originating at each WR. We compared the FA values at each ROI between the control and the patient group using multiple regression analysis (IBM SPSS Statistics 20). The independent variables included age, surgical treatment (control vs. patient group), surgery hemisphere (left vs. right) and resection region (frontal vs. parieto-temporo-occipital). Linear square means were compared by Tukey Honestly Significant Difference (HSD).Results: Within the control group, the FA values were higher at the genu (WR 2) and splenium of CC (WR 7) compared to other WRs of CC of the controls (p < 0.05). There was no significant difference in FA values between right- and left handers. In patients, the FA values were significantly lower at all WRs compared with the controls (p < 0.05). However, in WR6, the FA value was not significantly lower in patients with right hemispheric epilepsy or patients with frontal lobe epilepsy compared with the controls.Conclusions: Widespread decrease in FA values was found over all WRs in the patients compared with the controls. In WR6, which bilaterally connects to sensory and visual association cortexes including superior temporal, posterior parietal, insula and posterior cingulate cortices, FA values were spared mainly in the patients with right hemispheric epilepsy. This finding implies that bilateral connections of the association cortex through isthmus of corpus callosum may be preserved in right hemispheric epilepsy, when considering that stronger inter-hemispheric connections are known to be associated with increased corpus callosum size.