Abstracts

Rationale: The relationship between the irritative area (zone producing interictal spikes) and the ictal onset zone is still a central question in epileptology. The cellular mechanisms involved in interictal and ictal events are different, and could be influenced independently by different pathologies. We tried to evaluate the ictal-interictal relationship in different types of cortical development abnormalities (MCD) in order to better understand the generation of these activities. We used the non-invasive EEG-fMRI technique to record simultaneously all cerebral structures with a good spatio-temporal resolution.Methods: We recorded seizures in six focal epilepsy patients with a malformation of cortical development (MCD) (two dysplasia, three nodular heterotopia and one double-cortex). We performed a simultaneous recording of the EEG (21 MRI compatible scalp electrodes) and of the fMRI during two hours. The EEG was filtered offline and the interictal and ictal events were marked. Single analysis using the general linear model was done with all spikes types for each patient but seizures or group of similar seizures were analyzed separately. A statistic t-map was obtained in each case. We compared in particular the location of the BOLD activation between the interictal and ictal events in relation to the lesion.Results: One patient was recorded twice and two patients had two types of interictal events, resulting in nine interictal studies. The patients had either one ictal event or several similar events in three cases (11, 18 and 22). The ictal events were either electrical only or clinical with small motion. The lesion of dysplasia or of double cortex was always involved in the interictal and ictal process. The ictal BOLD increase was more spread. The three patients with a nodular heterotopia had a discrepancy between the ictal onset and the irritative zones. During interictal events, 60% showed a clear activation over the nodular heterotopia and 40% in the overlying cortex. On the contrary, all ictal events studies observed an important increase of the BOLD signal outside the lesion (at a different location of the interictal activation), maximum in the adjacent cortex.Conclusions: The precise location of the epileptic generators in MCD is still debated, in part because of the limitation of invasive studies. In this work, we demonstrated the usefulness of the EEG-fMRI technique in this exploration. The dysplasic cortex and the double cortex are able to generate interictal events and seizures. The nodular heterotopia may have the cellular substrate to generate interictal events, but does not appear capable of generating seizures, which are generated in the overlying cortex. This cortex is commonly microscopically abnormal with a dysplasic structure. One could hypothesize that only the structures organized in layer, even altered, can produce seizures in MCD. The BOLD study of interictal and ictal events in MCD patients could help understand the importance of the lesion and also determine the potential surgical target.(Rotary International, CIHR MOP-3879)