Abstracts

Rationale: Diffusion tensor imaging (DTI) has been increasingly used to distinguish focal abnormalities in partial epilepsy including mesial temporal lobe epilepsy (TLE). We examined the use of DTI in cases of TLE lacking adequate lateralization on preliminary noninvasive study to determine whether it might be used as a means of distinguishing those cases found to manifest independent bilateral temporal epileptogenicity.Methods: A retrospective review of archived cases of TLE identified cases of unilateral and bilateral TLE. Diffusion weighted MR images of 21 TLE patients (9 left, 7 right, 5 bilateral) and 11 nonepileptic subjects were analyzed using Tract-Based Spatial Statistics (TBSS) analysis. Fractional anisotropy (FA) maps were aligned into a common space using a nonlinear registration tool (FNIRT) which uses a b-spline representation of the registration warp field. A mean FA map for each group was created and thinned to create a mean FA skeleton representing the centers of all tracts common to the group. Each subject's aligned FA map was then projected onto this skeleton and the results fed into a voxel-wise cross-subject statistical analysis package. In addition to FA, maps of mean diffusivity (MD), ellipsoidal area ratio (EAR), parallel diffusion (PR) and perpendicular diffusion (PD) were generated. Each of the epilepsy groups (i.e., left, right, bilateral) was analyzed relative to the nonepileptic group and histograms of the p-values generated for comparison.Results: The right TLE group was shown to have significantly greater MD and PD values, whereas, the left TLE group harbored significantly greater MD, PD and PR values, in specific regions, than those of the nonepileptic group (p<0.05). The bilateral TLE group showed no diffusion parameters to be different than the nonepileptic group (p>0.2).Conclusions: Focal epileptogenicity appears to be associated with changes in the diffusion properties of specific regions in the brain that are detectable by TBSS analysis of diffusion MR imaging data. Bilateral epileptogenicity results in diffuse changes of no lateralizing value and may therefore preclude potential surgical candidates from further investigation.