Abstracts

Rationale: Temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS) is often associated with increased T2 relaxation time and decreased volume of the affected hippocampus (Coan et al; AJNR 2014; 35:77–83). Furthermore, it is well known that the hippocampus is a cornerstone of long-term memory function. However, it is increasingly recognized that TLE is a network disorder (Otte el al; Epilepsia 2012; 53:4, 659–667), and it involves several cognitive impairments with biological correlates that spread outside the temporal lobe (Dabbs et al; Epilepsy & Behavior 2009; 15, 445–451). Our goal was to evaluate quantitative measurements of both hippocampi in TLE patients with and without HS in comparison to controls, and to determine correlations between hippocampal measurements and thorough neuropsychological evaluation.Methods: Our Institutional Ethics Committee approved this study. We included 16 TLE patients without HS (no-MTS), 10 with left HS (L-MTS), 10 with right HS (R-MTS) and 25 controls. Images were acquired using a 3T scan with a 32-channel head coil. Volume measurements were derived from a T1-weighted volume (1x1x1 mm3 voxel dimensions). Relaxometry was computed from a multi-echo acquisition obtained with an oblique coronal orientation (TE1/TEspacing=15/15 ms; 8 echoes). Image processing: T1 volumes were automatically segmented using Volbrain (http://volbrain.upv.es/), and each hippocampus label was used as a region of interest for measurements. T2 relaxation time (T2) was obtained at each voxel by fitting a mono-exponential decay curve to the T2 images. Hippocampal volume (Vol) was expressed as the percentage of total brain volume. All patients and 12 controls underwent full WAIS-IV and WMS-IV neuropsychological assessment. Each hippocampus T2 and Vol were assessed between groups with ANOVA’s, followed by Tukey’s post-hoc test. Correlations between structural and neuropsychological measures were assessed with Spearman’s ρ. Statistical significance was defined as p<0.05.Results: There were no significant differences in demographic variables such gender, age, years of education, age of seizure onset or number of anti-epileptic drugs. With respect to controls, L-MTS and R-MTS had significantly reduced ipsilateral volume and increased T2. R-MTS patients showed reduced performance in the Working Memory Index (WMI) of the WAIS test (86.7±11.2 vs 105.1±8.8, for patients and controls respectively). No significant correlations between hippocampal measurements and neuropsychological tests were found in controls. Correlations found in TLE patients are shown in Table 1.Conclusions: Given that controls did not show correlations between their hippocampal structural measures and neuropsychological scores, correlations found in patients are presumably a result of the disease. Positive correlations in patients between contralateral hippocampal volume and neuropsychological assessments might be a compensating effect. On the contrary, presenting an increased T2 value in the contralateral hippocampus to the HS could indicate a higher cognitive impairment.