Diffusion tensor changes in epileptogenic hippocampus of TLE patients

Diffusion tensor imaging (DTI) can provide quantitative information of brain abnormalities in patients with temporal lobe epilepsy (TLE) that are not detectable with conventional magnetic resonance imaging (MRI).

Seventeen patients with medically TLE were selected for the study. The patients and ten healthy subjects underwent 25 directions DTI acquisition. The patients were separated into two groups based on the MRI findings: eight TLE MRI-negative patients with no signal abnormalities on conventional MRI and nine TLE patients with hippocampal sclerosis (HS). Fractional anisotropy (FA), mean diffusivity (MD), and the three diffusivities (lambda(1), lambda(2) and lambda(3)) were measured in bilateral hippocampi of controls, MRI-negative, and HS patients. Comparisons between the three groups were performed for hippocampi ipsi- and contralateral to epileptogenic zone.

The ipsilateral hippocampus of MRI-negative patients presented statistical increased anisotropy and no significant difference in diffusivities versus controls. Significant differences in anisotropy and diffusivities were detected between the ipsilateral hippocampus of HS when compared with controls.

DTI depicted hippocampal abnormalities in TLE patients with a normal conventional MRI different from those found in patients with HS. Diffusivity and anisotropy indices provide significant differences inside hippocampus and should be jointly considered to improve the DTI measurements specificity in TLE patients.