[Features of ictal and interictal electrical activity in assessment of the epileptogenic zone in children with focal cortical dysplasias].

Currently, there is no single standard defining what rhythmic activity should be considered as the area of ictal pattern onset. Differences in electroencephalographic patterns associated with different types of focal cortical dysplasias (FCDs) have not been defined. Aim - we aimed to identify features of the ictal onset pattern on a scalp EEG, depending on the histology, location, and extension of epileptogenic zone, as well as to elucidate the relationship between concordance of the interictal and ictal activity localization and ictal onset pattern types.

MATERIAL AND METHODS: We studied scalp video-EEG monitoring data of 38 FCD patients who underwent surgical treatment for intractable epilepsy in the period between 2010 and 2016. We analyzed the data on interictal and ictal activity localization and compared them with the data on FCD types and lesion location.

RESULTS: Two types of the ictal onset pattern on EEG, local and generalized, were identified. The local and generalized types included two and four variants of the ictal onset pattern, respectively. Therefore, 6 combinations of rhythmic activity were identified, which manifested within the first 10 s after the onset of electrographic changes on EEG simultaneously with initial clinical manifestations of seizure. Co-localization of the interictal and ictal activity zones occurred in 42% of cases; of these, 88% of patients had the ictal onset pattern. In the remaining cases (58%), no co-localization of the interictal and ictal activity zones was detected; of these, 76% of patients were assigned to the group with the generalized ictal onset pattern. The local ictal onset pattern was more common in patients with type II FCD, while the generalized ictal onset pattern was more common in patients with type I and type III FCD. No correlation between the ictal onset pattern type and the lesion localization was found.

CONCLUSION: We describe two ictal onset pattern types, local and generalized, on EEG in children with FCD. The co-localization of ictal and interictal activity zones prevails in the local ictal onset pattern group. The local ictal onset pattern is often associated with type II FCD. In the case of type I and type III FCD, the generalized ictal onset pattern predominates. There is no clear relationship between the ictal onset pattern type and the lesion location.