Abstracts

RATIONALE: Diffusion tensor imaging (DTI) is a novel MR technique which allows visualization of white matter (WM) tracts by detecting the dominant direction of water diffusion. In epilepsy, DTI has been used to assess distortion of WM tracts associated with seizure foci. Functional MR (fMR) allows demonstration of functionally active neuronal tissue during a specific task. We combined the two techniques to search for disturbances of functional brain organisation associated by WM damage.
METHODS: We studied 8 patients with chronic epilepsy on a 3T scanner (GE medical systems). DTI was acquired in each patient (b=3000, 7 directions. 17 slices, 6 mm thick, 1.5 gap) and post-processed using Functool. fMRI used two different language tasks (noun-verb generation and orthographic lexical retrieval). Lateralisation of language was assessed based on the post-processed, motion corrected images. Based on 30 controls, language lateralisation was considered [ssquote]typical[ssquote] if [gte] 60% of the total activation was on the left. Additional investigations included T1 anatomical imaging, FLAIR, and whole brain T2-relaxometry.
RESULTS: Four patients had hippocampal sclerosis (HS) in the dominant hemisphere. Two of them had atypical language lateralization (table). Both showed asymmetric WM tracts in the fronto-temporal region. T2-relaxometry was increased in the ipsilateral hippocampus in both patients ([gte] 114 mesc, normal [lte] 107 msec), but normal in the frontal and temporal WM. The other two HS patients had typical language lateralisation and normal DTI.
Four patients had dysplastic lesions. Two patients had dysplasias in the dominant hemisphere, and both had atypical language lateralization. DTI was abnormal in one patient with left temporal dysplasia, but normal in one patient with a small left frontal pole dysplasia. Both patients with right-sided dysplasia showed typical language lateralization, WM tracts were abnormal in one of these patients.
CONCLUSIONS: Six of the eight patients had a lesion in their dominant hemisphere. Four of these patients showed atypical langage lateralization. In three of these patients, all with temporal lobe lesions, DTI showed a distorsion of the WM tracts. Both patients with left-sided lesions, but typical language, had normal DTI. Therefore, this first report of a combination of DTI and fMRI in a series of epilepsy patients suggests that a left-temporal lesion with associated DTI abnormalities may have consequences on language lateralisation.[table1]
[Supported by: Brain Imaging Research Foundation, Australia]