Abstracts

RATIONALE: Structural and metabolic abnormalities in the hippocampal region in mTLE are well described. However, epileptogenic activity often spreads to other brain regions. Neuropsychological, volumetric and metabolic abnormalities beyond the hippocampus have been reported. The aim of this study was to identify extrahippocampal and extratemporal brain regions with reduced NAA/(Cr+Cho) in individual patients suffering from mTLE with (TLE-MTS) and without (TLE-no) MRI evidence for mesial-temporal sclerosis using 1H multislice magnetic resonance spectroscopic imaging (MRSI).
METHODS: MRSI in combination with tissue segmentation was performed on 21 patients with mTLE and 12 age-matched healthy volunteers. In controls, the metabolite ratios (NAA/Cr+Cho) of all voxels of a given lobe (frontal, parietal, etc) were expressed as a function of white matter content using a linear regression analysis to determine the 95% prediction interval for any additional voxel of a given tissue composition. Voxels with metabolite ratios below the lower limit of the 95% prediction interval were defined as [dsquote]pathological[dsquote] in patients and controls. The localization of voxels defined as [dsquote]pathological[dsquote] was indicated on the corresponding MRI slice for anatomical reference. Z-scores were used to identify brain regions of mTLE subjects with a percentage of pathological voxels greater than in controls.
RESULTS: In mTLE patients, extrahippocampal and extratemporal brain regions with (NAA/Cr+Cho) lower than in controls could be identified in the ipsi- and contralateral insula and frontal lobes and in the ipsilateral temporal and parietal lobes (cf. Table 1). The frontal limbic and prefrontal regions were more often affected than the lateral frontal regions. There was no difference between the ipsi- and contralateral hemispheres. There were no differences of extent and distribution of extrahippocampal NAA reductions between TLE-MTS and TLE-no.
CONCLUSIONS: In mTLE extrahippocampal and extratemporal reductions of NAA/(Cr+Cho) were found in the frontal lobes, insula and ipsilateral temporal and parietal lobes; but there were no differences between ipsilateral and contralateral sides. The preferential involvement of brain areas directly and indirectly synaptically connected to the medial temporal structures may indicate that the abnormal extrahippocampal regions represent brain regions involved in seizure spread.[table1]
[Supported by: The study was supported by NIH Grant R01-NS31966
SGM was supported by a Grant from the Swiss National Science Foundation.]