Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most common focal epilepsy syndrome in adults. Seizure related, excitotoxic damage may occur along normal physiologic pathways in limbic system and it can cause wallerian or transneuronal degeneration in the circuitry. Cingulum is a visible white matter tract in limbic system and contains extensive afferent and effect connections with mesial temporal lobe structures. Exploring DTI findings of cingulum in unilateral refractory TLE could reveal the extent and downstream effect of the disease. We therefore analysed the diffusion properties of cingulum, compared the measurements with healthy controls and determine the ipsilateral differences in each patients. Methods: We retrospectively analysed DTI images of cingulum in 27 unilateral refractory TLE (17 left, 10 right) and age matched healthy controls. All patients have been diagnosed TLE based on scalp or invasive ictal and interictal EEG findings, seizure semiology and neuroimaging results. patients with lesions other than mesial temporal sclerosis on the MRI were excluded from the study. Diffusion images were processed by using "DTI-studio" computer program that allows diffusion tensor calculations, fiber tracking, color mapping and region of interest (ROI) drawings. Each ROI was defined as 2x2 rectangular pixels (1 pixel= 0.94 x 0.94 x 4 mm3). Certain numbers of ROIs were chosen in 3 subregions of cingulum; 1 ROI in anterior, 4 ROIs in superior and 2 ROIs in descending part. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial and perpendicular diffusivities were measured for the each ROIs. All DTI measurements were stored in excel data sheet and findings were compared within two hemispheres as well as with age matched healthy controls. The significance of the differences was assessed using Student's t-test and the significance levels were set at p=0.05 (two-tailed test). Results: When control subjects evaluated seperately, no differences were found in ADC and FA values in both hemispheres. Left side has increased axial diffusivity in the superior portion of the cingulum only. However, in left TLE patients, ADC and axial diffusivity was higher on the ipsilateral side, p=0.005 and p=0.01 respectively. In right TLE, ipsilateral FA was decreased significantly (p=0.01) and perpendicular diffisuvity was increased (p=0.01). Left and right TLE findings were also compared with controls and results were shown in the table below. There were significant abnormalities in FA values of the descending part and anterior part of the cingulum ipsilateral to left TLE and right TLE respectively. Conclusions: The results suggest that unilateral refractory TLE has a detrimental effect on ipsilateral cingulum, consistent with white matter axonal and also myelin degeneration. Further studies with different subgroups of TLE would improve our understanding on the possible pathophysiologic role of the cingulum in mesial temporal sclerosis and non-lesional TLE patients.