Abstracts

In temporal lobe epilepsy (TLE), morphometric MRI studies have shown extra-hippocampal structural damage. These studies are labor-intensive, focus on few areas and suffer from low intra- and inter-rater reliability.
Voxel-based morphometry (VBM) is an automated technique allowing identification of differences in grey matter (GM) and white matter (WM) with no a priori region of interest, enabling whole brain analysis between groups.
The purpose of this study was to determine whole-brain GM and WM abnormalities in TLE using VBM.
We studied 87 patients with intractable TLE (mean age: 35 yrs), and 51 neurologically normal controls (mean age: 33 yrs). Seizure focus was defined as right (n= 40) or left (n=47) if more than 70% of seizures were recorded from one side. Volumetric MRI showed ipsilateral hippocampal atrophy in all patients.
MRI 3D-images were acquired on a 1.5 T scanner using a T1-fast field echo sequence (slice thickness =1mm). Image processing included: (i) automated correction for intensity non-uniformity; (ii) normalization of grey-level intensities; (iii) linear registration of images to a standardized stereotaxic space; (iv) classification of brain tissue into GM, WM and CSF; (v) blurring of GM and WM binary masks with an isotropic Gaussian kernel of 5 mm FWHM to generate 3D-maps of GM and WM [ldquo]density[rdquo]. Statistical maps of differences between patients and controls densities were obtained using a general linear model. Significance was set at p[lt] 0.05, corrected for multiple comparisons.
GM reduction: Compared to normal controls, patients with left and right TLE had diffuse GM reduction in the hippocampus ipsilateral to the seizure focus. In patients with left-TLE, GM reduction was also present in the contralateral hippocampal tail. Both patient groups had ipsilateral GM reduction in various frontal lobe areas (prefrontal, dorsolateral prefrontal, orbitofrontal, central, and cingulate). In patients with left TLE, ipsilateral reduction was also present in the insular and superior temporal cortices. Contralateral GM decrease was present in frontal and occipital areas in left-TLE patients and in the superior temporal gyrus in right-TLE patients. In addition both groups had bilateral thalamic GM reduction.
WM reduction: patients with left and right TLE showed a diffuse reduction of temporal lobe WM (temporo-polar, entorhinal, superior temporal, temporal stem, and fusiform) ipsilateral to the seizure focus, and decrease WM in the body of corpus callosum. Right-TLE patients had ipsilateral WM reduction in the frontal and post-central areas.
GM pathology in TLE extends beyond the hippocampus involving mainly the frontal lobe and the thalamus. Ipsilateral WM reduction is present in the anterior temporal lobe. This pattern of abnormalities is compatible with preferential degeneration of reciprocal parahippocampal-frontal and parahippocampal-thalamic pathways connecting areas responsible for attention and memory processing.