Abstracts

RATIONALE: Approximately 15% of patients with intractable temporal lobe epilepsy (TLE) do not have detectable hippocampal atrophy on MRI. In patients with TLE and hippocampal atrophy, we have demonstrated MRI evidence of entorhinal cortex (EC) and perirhinal cortex atrophy ipsilateral to the epileptic focus (N. Bernasconi, Neurology, 1999 & Ann NY Acad Sci, 2000). We hypothesized that MRI volumetric measurement of the EC can detect structural damage and help lateralizing the epileptic focus in TLE patients who do not have hippocampal atrophy. METHODS: MRI volumetric analysis of the EC was performed using a T1-weighted 3D gradient echo sequence in 24 healthy subjects, and 22 TLE patients with normal hippocampal volume. The epileptic focus was left-sided in 12 patients and right-sided in 10. Twelve patients were operated. RESULTS: Group analysis (MANOVA) showed a significant reduction in the volume of the EC ipsilateral to the seizure focus in patients with left TLE (p<0.0001) and right TLE (p<0.0001). Individual analysis, based on a 2SD cutoff from the mean of normal controls, showed a significant reduction in the volume of the EC in 17/22 (77%) of TLE patients. In 14/22 (64%) the EC atrophy was ipsilateral to the seizure focus. In 3/22 (14%) EC atrophy was bilateral. The EC volume was normal in 5/22 (23%) patients. CONCLUSIONS: TLE patients with normal hippocampal volume have a reduction in volume of the EC ipsilateral to the seizure focus. Therefore, EC atrophy supports the presence of structural damage in the mesial temporal lobe in this group of patients. Volumetric measurement of the EC is of practical use in the MRI investigation of TLE patients, particularly in the absence of hippocampal atrophy.