Abstracts

Rationale: Hippocampal atrophy has been reliably identified using volumetric techniques coupled with high resolution MRI in patients with drug resistant temporal lobe epilepsy. Although hippocampal atrophy is the most common finding in temporal lobe epilepsy, studies using MRI have also shown abnormalities in the surrounding areas of the medial temporal lobe. A study by Bernasconi et al. (Brain, 2005; 128: 2442-2452) found differences in the depth and angle of the collateral sulcus in patients with temporal lobe epilepsy who had suspected malformations of cortical development. In a previous study from our laboratory, we quantified the abnormalities in these patients by identifying increases in the volume of the collateral sulcus using manual volumetrics. This study aims to further quantify these changes by determining if cortical thickness in the collateral sulcus can differentiate these patients from controls. This may help in the understanding and better identification of epileptogenic areas in patients with temporal lobe epilepsy. Methods: This study examined 6 patients with unilateral left temporal lobe epilepsy, as determined by long term video-EEG monitoring, and 8 age matched control subjects. Those with left temporal lobe epilepsy were selected based on the properties of the ipsilateral collateral sulcus (i.e. deeper and more vertical than other patients with temporal lobe epilepsy). T1 weighted 3-D SPGR pulse sequence MRI images were acquired in all participants. Bilateral hippocampal volumes were derived by manually tracing consecutive T1 coronal slices and cortical thickness measurements of the collateral sulcus gray matter were acquired using Freesurfer software. Finally, statistical analyses were performed in the Freesurfer module comparing the two groups. Results: Of the 6 patients with left temporal lobe epilepsy 2 had left hippocampal atrophy, the other 4 patients had normal bilateral hippocampal volumes. The results showed a significant (p<0.05) increase in cortical thickness in the area of the left but not right collateral sulcus gray matter. Conclusions: This study was performed to investigate if an increase in cortical thickness of the collateral sulcus gray matter could identify a unilateral cortical abnormality even without the presence of hippocampal atrophy. The increased cortical thickness in this area may be attributed to abnormal cortical development and may be identified as a target for surgical resection. Identifying extrahippocampal epileptogenic areas is important in determining the appropriate surgical approach to reduce seizure frequency in those with intractable temporal lobe epilepsy.