Abstracts

Rationale: Generalized onset seizures are conceptualized as originating and rapidly engaging bilateral distributed network with no clear focus. The early centrencephalic or universalizer theory suggested a subcortical origin of generalized seizures, which provided little to no role for corpus callosum in bilateral epileptic network. Later, the corpus callosum was shown to be an important pathway for synchronizing bilateral discharges. Therefore, corpus callosotomy is often performed as a palliative treatment for refractory drop seizure.However, the possibility of coupling/resonance between cortical focus and subcortical structures triggering rapidly generalized epileptiform discharges has been documented. Our previous studies have shown that, in some patients with generalized seizures, a focal seizure onset might be discovered once corpus callosotomy disrupted the bilateral epileptic network between two hemispheres. Corpus callosum is considered to be a major hub of the bilateral epileptic network for seizure propagation in this group of patients. The role of corpus callosum in this scenario of seizure generalization could be different from bilateral synchronization with no focus. We hypothesized that, through analysis of diffusion tensor imaging (DTI), we could differentiate structural difference of corpus callosum between the patients with lateralized seizures after corpus callosotomy and the patients with non-lateralized seizures after corpus callosotomy. Methods: We retrospectively reviewed 24 patients diagnosed with refractory generalized epilepsy having generalized onset motor seizures. All patients had negative MRI finding and later underwent corpus callosotomy in this study. Based on the post corpus callosotomy EEG evaluation, the patients then were divided into lateralized seizure group and non-lateralized seizure group.DIT images were acquired to investigate the structural integrity of corpus callosum. The processing of DTI data utilized FSL software package to create anisotropy (FA) and mean diffusivity (MD) maps for quantifying the structural altercation in corpus callosum between two groups. Voxelwise statistical analysis of the diffusion maps was carried out using the method of Tract-Based Spatial Statistics (TBSS). Results: 24 patients with generalized onset motor seizures were recruited in this study where 10 of them developed lateralized seizures after corpus callosotomy and the rest 14 patients continued having non-lateralized seizures. There was no significant difference between these two groups in terms of age, gender, seizure history, and seizure frequency.When comparing difference between lateralized and non-lateralized groups by DTI analysis of corpus callosum, significant FA reduction was found in the body of corpus callosum in lateralized seizure group. The body of corpus callosum also demonstrated higher mean MD value in lateralized seizure group over non-lateralized seizure group. However, difference is not statistically significant. Conclusions: When patients with generalized epilepsy experience post callosotomy seizure lateralization, it indicates that corpus callosum is an important part of bilateral epileptic network. The results further demonstrate that the corpus callosum as a major path of the bilateral epileptic network in lateralized seizure group suffers greater damage than non-lateralized group by showing reduced FA value. The study suggests that DTI analysis of corpus callosum might predict the seizure lateralization in generalized epilepsy after corpus callosotomy. Funding: Not applicable