Abstracts

Rationale: There remains much to learn about how focal aberrant neuronal excitation may affect surrounding and distant brain function and anatomy. The aim of this study was to assess the functional connectivity between areas of abnormal neuronal excitation in children with intractable temporal lobe epilepsy. Methods: Six pediatric patients with intractable epilepsy secondary to a variety of primary etiologies, had magnetoencephalography (MEG) performed. MEG showed both temporal and Rolandic dipole clusters in a unilateral hemisphere. Diffusion tensor imaging (DTI) tractography was then performed on each patient. DTI tractography was also peformed on six age and sex match controlled subjects with normal brain morphology for comparison. Results: In all patients, a consistent white matter tract traveling through the external capsule, connecting the temporal and Rolandic regions of MEG activity was visualized. However, on the contralateral hemisphere in each patient, there was no evidence of a similar fiber tract connection, linking the corresponding identical volumes between the two regions. Six age-matched, control subjects with normal brain morphology were studied for comparison. There were no corresponding white matter tracts identified in either hemisphere within this subset. Conclusions: This is the first identification of novel association white matter tract formation through the external capsule, connecting two distant sites of unilateral epileptiform MEG activity. The notable absence of the corresponding tract on the contralateral hemisphere of the epilepsy patients and within the normal control subset, may indicate that the chronic interictal epileptogenic discharge could play a causal role in the de novo organization of these newly identified tracts. This finding may highlight the role of active white matter tract reorganization and plasticity in the pathophysiology of epilepsy.