Abstracts

The majority of seizures in patients with Temporal Lobe Epilepsy (TLE) may be segregated into two groups based on electrographic onset pattern. Low-voltage fast (LVF) onsets are characterized by high-frequency, low-amplitude activity, while hypersynchronous (HYP) onsets consist of long-lasting ([gt]5 s) trains of low-frequency ([lt]2 Hz), high-amplitude spikes (Velasco et al., 2000, Neural Plast, 7: 49-63). Differences in voltage-depth profiles indicate LVF and HYP seizures onsets may arise via different mechanisms (Bragin et al., 2005, Epilepsia, 46(S5): 59-63). To determine whether structural differences may be associated with these two onset types, hippocampal surface contour mapping was used to map the distribution of local hippocampal atrophy in the two groups., Intracranial depth electrode recordings (0.1-70Hz) of 61 seizures from 16 patients were analyzed. Patients were assigned to the LVF or HYP group based on predominant type of seizure onset. Using surface contour modeling techniques (Thompson et al., Neuroimage, 2004, 22:1754-1766), 3D hippocampal parametric mesh models were created for the 16 patients and for 16 age- and sex-matched controls. Patient and control models were divided Ipsilateral (Ipsi) and Contralateral (Contra) groups based on side of seizure onset. Normalized hippocampal volumes were determined and 3D maps of local hippocampal atrophy were generated., Whole hippocampal volume measures show significant reductions (25%) ipsilaterally in both LVF (t-test P = 0.0003) and HYP (P = 0.003) onset groups. Though both groups display the same level of atrophy, contour maps reveal two distinct distributions. HYP atrophy is concentrated medially, while LVF atrophy appears mainly on the lateral aspect of the model. Analysis of contralateral hippocampal volumes revealed an absence of atrophy within the HYP Contra group (P = 0.53), while the LVF Contra group had a significant reduction in volume (P = 0.04) compared to controls. Atrophy was distributed laterally as it was in the LVF Ipsi group., In TLE patients with low-voltage fast seizure onsets, contralateral hippocampi show significant levels of atrophy when compared to controls. This is in contrast to patients with hypersynchronous onsets, where no significant atrophy is observed contralaterally. This difference may reflect the more diffuse nature of seizure generating regions in LVF onsets and the more localized nature associated with HYP onsets. Further analysis of the distribution of atrophy in these groups may allow us to better characterize the mechanisms of seizure generation., (Supported by NIH grants NS 02808 and NS 33310.)