Abstracts

Rationale: Previous DTI studies suggested bilaterally widespread abnormalities beyond epileptogenic zone in medically intractable focal epilepsy. This study aimed to investigate the post-operative changes in the major white matter fibers for children with medically intractable focal epilepsy secondary to focal cortical dysplasia (FCD). Methods: Thirty patients with medically intractable focal epilepsy had both pre-operative and post-operative Diffusion tensor imaging (DTI) at the Children's Hospital of Alabama. The mean age at surgery was 10.0 ± 4.7 years (1 year 11 months-16 year 2 months). Only thirteen (43.3 %) had visible lesions on conventional, pre-operative brain MRI. Most patients (29/30) underwent intracranial EEG monitoring prior to surgery. Twenty had seizure onset zones in fronto-parietal regions including frontal lobe localization (10) while the rest had in temporo-occipital seizure onset zones including temporal lobe localization (6). The mean post-operative follow-up duration was 31.2 ± 11.2 months (10-51 months). Twenty-six patients (86.7%) have favorable outcomes (Engel class I-17, II-9). The pathology was FCD in all cases: Type IA (4), Type IB (1), Type IIA (19), and Type IIB (6). One patient had also focal meningeal angiomatosis. Age at pre-operative MRI and time between pre- and post-operative MRIs were 9.3 ± 4.6 years and 12.5 ± 6.3 months, respectively. The Regions of interest (ROIs) for the major white matter tracts included the genu and splenium of the corpus callosum (CC), the posterior limb of the internal capsule (CST), the inferior fronto-occipital fasciculus (IFO), the inferior longitudinal fasciculus (ILF), the superior fronto-occipital fasciculus (SFO) and the superior longitudinal fasciculus (SLF). Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were determined in each ROI. A matched-pairs t-test was used to assess statistical significance of differences between pre- and post-operative values at each ROI. Results: Compared to pre-operative values, post-operative FA values were significantly lower and ADC values higher in CC genu and IFO ipsilateral to the resection (p <0.05). In SLF ipsilateral to surgery, the post-operative FA values were decreased (p <0.05) but the post-operative ADC values were not significantly different from the pre-operative ones. In ipsilateral ILF, the post-operative ADC values were higher (p <0.05) but the post-operative FA values were not significantly different from the pre-operative ones. In CC genu, ipsilateral IFO, and ipsilateral SLF, λ1 values showed no significant difference, while λ2 and λ3 values were significantly increased (p <0.05). Conclusions: The post-operative pathologic changes occurred mainly in white matter fibers ipsilateral to the resection. When considering the post-operative changes were not significant in the contra-lateral side, the epilepsy surgery may block the progression of diffuse pathologic changes, which were observed in medically intractable focal epilepsy, in the contra-lateral side to operation.