Abstracts

Rationale: To investigate the micro-structural pathologic changes involving the major white matter fibers in children with medically intractable focal epilepsy Methods: Twenty-one children with medically intractable focal epilepsy had both pre-operative Diffusion Tensor Imaging (DTI) and epilepsy surgery at the Alabama Children s Hospital in 2008-2009 (Patient group). Thirteen had surgery in the left hemisphere and 8 in right hemisphere. The mean age at epilepsy surgery was 9.50 4.58 years (1 year 8months - 15 year 8 months). The mean post-operative follow-up duration was 16.0 7.20 months (7-28 months). Fifteen (71.4%) have been seizure-free postoperatively. Ten (50%) had visible lesions on the conventional brain MRI pre-operatively. The most common pathology was focal cortical dysplasia (85.7%). Thirty-six, age-matched, healthy controls were compared (Control group). Control data were obtained from a normal pediatric database, which was collected under Human Brain Project and National Research Resource Center Grants (cmrm.med.jhmi.edu). Data from both patients and controls were transferred to the workstation and processed using DTI studio software (http://lbam.med.jhmi.edu/DTIuser/DTIuser.asp) and maps for fractional anisotropy (FA) were created. Regions of interest (ROIs) were outlined bilaterally on axial slices of the colored FA map, which were confirmed by fiber tractography. The ROIs for the major white matter fibers include the genu and splenium of the corpus callosum (commissural fibers), the posterior limb of the internal capsule (projection fibers, chiefly of the cortico-spinal tract), the inferior fronto-occipital fasciculus, the inferior longitudinal fasciculus, the inferior fronto-occipital fasciculus and the superior longitudinal fasciculus (association fibers). FA was determined in each ROI. Statistical analysis used ANCOVA with age and group as independent variables. Results: In the patient group, the FA values were significantly lower at the genu and splenium of the corpus callosum, right corticospinal tract, bilateral inferior fronto-occipital fasciculus, left inferior longitudinal fasciculus, bilateral superior longitudinal fasciculus compared to controls (p<0.05) (Figure 1). Decreased FA values were more prominent in the patients who had surgery in the left hemisphere compared to controls (p<0.05) (Figure 2). Conclusions: Decreased FA values suggest that the pathologic changes extend diffusely to most of major white matter fibers in children with medically intractable focal epilepsy.