Abstracts

Rationale: Malformations of cortical development (MCD) represent one of the most common cause of medically-intractable focal epilepsy, particularly outside the temporal lobes. The advent of high-resolution MRI has allowed us to identify these malformations, as well as associated anomalies in the hippocampi. For instance, recent studies have shown enlarged and abnormally rotated hippocampi in patients with MCDs that were due to abnormal migration, which make us consider that perhaps these patients had early findings of dual pathology. DTI is a very sensitive method for detection of subtle abnormalities in the brain. The use of this technique may allow us to identify hippocampal abnormalities even in earlier stages. We present a cohort of patients with epilepsy due to MCD, and we assessed their hippocampi and compared the findings with control cases.Methods: six patients with extra-temporal lobe epilepsy (2 with cortical dysplasia, 2 with heterotopia, and 2 with polymicrogyria) and 4 controls were studied. All MR scans were performed on a 3T Siemens Trio with a 32 channel head coil. Diffusion images were acquired with a diffusion weighted spin-echo echo-planar imaging sequence (TR/TE=9000/ 90 ms, FOV= 256x256, matrix=128x128,voxel size = 2 isometric, b value= 1000 s/mm2). Diffusion weighted scans were acquired in 64 optimized directions. High resolution T1-weighted data was also acquired with a MPRage sequence. The diffusion data was reconstructed and analyzed using Brainvoyager QX software. Left hippocampus and right hippocampus were selected as the volume of interest. In the present study four DTI parameters were used to quantitatively analyze the volume of interest, they were fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AxD) and radial diffusivity (RD)Results: Figure 1 shows decrease in the fractional anisotropy and figure 2 shows increased mean diffusivity in the hippocampi of patients with MCD compared to controls. RD and AxD were increased, particularly RD.Conclusions: Decreased FA in patients compared to controls, suggests degradation of white matter tracts while increased MD suggests reduced cellular density. The findings indicate a structural alteration in the hippocampi of patients with extra-temporal epileptic MCD. The clinical significance of these findings are currently unknown, but indicate early changes in the hippocampi not noticed otherwise with conventional structural and functional imaging