Abstracts

We investigated the sensitivity of short echo time hippocampal ¹H-MR Spectroscopy in lateralization of the affected hemisphere in 15 MRI negative patients with temporal lobe epilepsy (TLE). Patients without pathologic findings in high resolution MRI were consecutively scheduled for focus evaluation by intensive video EEG monitoring. In all patients with a temporal focus localization (n=15) short term single voxel spectroscopy of temporomesial structures were carried out. Spectral analysis and metabolite quantitation of N-acetylaspartate (tNAA), Cholin (Cho), Creatin (Cr), total glutamate plus glutamine (Glu+Gln) and myo-Inosidol (Ins) in the hippocampus were carried out using LC-Model, using water as an internal reference. Normal ranges were established by the 95% confidence interval of age matched controls. The significance of the difference of metabolite means between the affected hemisphere of patients and normal values of controls were measured by unpaired students t-test. The correlation between the degree of metabolitealteration (z-scores) and the degree of seizure activity in EEG findings was estimated by Pearson coefficient. 6 patients were classified as unilateral by EEG investigations 4 of them with unilateral left hemiospheric focus and 2 of them unilateral right hemispheric focus. 9 patients showed a bilateral focus localization. 7 of 11 (9 bitemporal+2 unilateral) patients with an EEG focus located in the right temporal lobe demonstrated significant NAA reduction in the right hippocampus while 10 of 13 (9 bitemporal+4 unilateral) patients with an EEG focus located in the left temporal lobe demonstrated significant metabolite alterations in the left hippocampus. Additionally the degree of spectroscopic metabolite alterations was correlated to the degree of pathologic findings in interictual EEG activity. (Pearson coefficient: -0.709** for absolute tNAA in the right hemisphere and -0.45 for absolute tNAA in the left hemisphere). Our results show that, if optimized and standardized techniques are used, ¹H-MRS provides lateralizing information in MRI negative TLE patients which can be added to EEG findings in focus localization. Metabolite alterations correlated at high level of concordance between the degree of EEG abnormalities in the right hemisphere and at a moderate level in the left hemisphere. (Supported by Wilhelm Sander foundation)