Abstracts

Cerebral cavernous angiomas (CCAs) are frequently associated with focal intractable epilepsy, and their epileptogenicity is usually attributed to the rim of hemosiderin deposits. Co-recording of EEG and fMRI is a new method to investigate the effects of epileptic discharges in the focus and at distance. We used EEG-fMRI to identify BOLD responses to interictal spikes in patients with CCAs. Spikes were marked according to spatial distribution, with each spike type determining one EEG-fMRI study. Combined maps of t-statistics were created to assess positive (activation) and negative (deactivation) changes in BOLD signal related to the spikes. Responses were analysed in the lesional and perilesional area, and at distance. The raw fMRI signal in the lesion and its boundaries was evaluated for signal loss due to the susceptibility artefact associated with the lesion and the hemosiderin. Eight patients, three with multiple CCAs, were scanned, all with temporal lobe epilepsy and spikes. One patient had bilateral spikes, analyzed separately, and three studies with less than two spikes were excluded. Therefore, six studies were analyzed, all showing BOLD responses: four had only activation, one had only deactivation and one had both responses. No response was found in the lesion itself or immediate periphery, and the raw fMRI signal showed loss in lesional and perilesional areas in all patients. Responses involved the perilesional area in 2/6 studies, both concordant with the spike topography, one as activation and the other one as deactivation. In all patients, areas of BOLD responses were identified at distance from the lesion. In the four studies where the spikes were ipsilateral to the temporal CCA, there was activation in that temporal lobe. In the two studies where the spikes were contralateral to the temporal CCA, the response was concordant with the spike in one study, and unrelated to either the spike or the lesion in the other one. Despite susceptibility artifacts caused by iron deposits, we demonstrated EEG-fMRI responses involving the perilesional areas in 33% of studies, supporting their role in epileptogenicity of CCAs. The frequently distant responses are in accordance with previous studies in lesional and non-lesional temporal lobe epilepsy. These responses may be the result of distant effect of spikes, which, in CCAs, could be enhanced by the possible presence of non-visible microvascular lesions. (Supported by The Canadian Institutes of Health Research (CIHR), Preston Robb fellowship from the MNI and the Savoy Foundation for Epilepsy.)