Abstracts

Rationale: There is an extensive literature indicating widespread cortical and subcortical damage in patients with chronic temporal lobe epilepsy (TLE). Less is known about the extent of progressive atrophy over time. In this study, we use a longitudinal design to compare the 4-year MRI volume changes in TLE and controls. Here, we present findings for cortical lobar regions, hippocampus, parahippocampus, entorhinal cortex, cerebellum, thalamus and ventricle size. These regions have shown reliable findings of volume abnormality in TLE, but there has been very little study of their change in brain volumes over time. Methods: Structural MRI volumes of 17 TLE patients (mean age = 35.1) and 26 age-matched controls were examined at baseline and at 4-year follow-up. TLE patients had a long duration of chronic epilepsy (mean = 24.2 years). No patients underwent surgery in the test-retest interval. FreeSurfer, an automated program used to reconstruct the cortical surface and subcortical structures of the brain was used to determine volume changes. Percent volume change over the four year interval was calculated for each subject and Cohen s d effect sizes were calculated to compare mean differences between groups. Conventional interpretation of Cohen s d classifies effect size findings as small (.2-.5), medium (.5-.8) and larger (>.8). Results: A distributed pattern of greater lobar volume loss for the TLE group was found in the right medial temporal region (d = .54), left frontal (d = .41), right parietal (d = .44) and right (d = .48) and left occipital lobes (d = .43). Small effect sizes were also noted in the right (d = .44) and left cerebellar cortex (d =.39), with greater volume loss in the TLE group. Total hippocampus volume (d = .58), parahippocampas volume (d = .41), entorhinal cortex (d = .67) showed small to medium effect size effects for volume loss in the TLE group compared to controls. Group differences in ventricular enlargement also showed moderate to strong effect size differences; third ventricle (d = .80 ), left lateral ventricle (d =.54 ), right lateral ventricle (d =.66) and fourth ventricle (d = .45). The thalamus volume difference between groups did not reach levels considered to be a small effect size (d = .04). Conclusions: The current study indicates widespread volume loss over a four-year interval in chronic TLE. Small to medium effect size differences were found in a distributed set of cortical regions, hippocampus, parahippocampus, enthorhinal cortex, and cerebellum. The strongest effect size was found for the third ventricle. These findings suggest that brain atrophy in TLE continues to progress even in TLE patients with a long duration of epilepsy. Determining factors associated with individual differences in volume loss would be of considerable value.