Abstracts

Prediction of ictal onset zone by subdural interictal spike pattern has rarely been analyzed. The objective of our study was to analyze the relationship between interictal spikes and ictal onset zones on subdural EEG recordings., Fifteen patients (aged 25 to 61 years) undergoing prolonged subdural intracranial EEG recordings were included. On average 92 electrodes (range 42 to 119) were implanted. Representative interictal and ictal EEG recordings were reviewed.
Interictal spike populations were identified by voltage from baseline, earliest onset, frequency of the spike population, presence of an aftergoing slow wave and duration. Distribution of the interictal activity was defined as 80% fall-off from the maximum. The electrodes with the earliest rhythmic evolution determined the ictal onset. The relationship between interictal EEG and ictal onset electrodes was analyzed., Interictal spikes were seen from a discrete single focus in five patients, from two different foci in six patients and were multifocal or diffuse in four patients. Ictal onset was seen from circumscribed areas in 14 patients and was diffuse in one patient. Cases with more than one spiking pattern were not associated with a higher number of implanted electrodes.
Single EEG seizure patterns were recorded in eight patients. In five patients two different EEG seizure patterns were recorded, one patient had three different EEG seizure patterns and one additional patient had five different EEG seizure patterns. Interestingly, cases with more than one subdural EEG seizure pattern were associated with a higher number of implanted electrodes (p[lt]0.05).
In eight patients (53%) the most frequent spike focus was concordant with a subdural EEG seizure onset zone. Six out of these eight patients presented with only one subdural EEG seizure type. One of these eight patients presented with very broad spikes, but their maximum was concordant with the ictal onset zone. In three additional patients (20%) the most frequent or second most frequent spike population occurred one or two electrodes (1-2 cm) adjacent to a seizure onset zone. In three patients diffuse spiking was seen whereas the seizure onset was focal. One patient had diffuse seizure onset with focal spikes., Ictal onset zones on subdural EEG recordings were related to the most frequent subdural interictal spike focus in 53% of cases. After inclusion of the second most frequent spike focus and surrounding electrodes, an ictal onset zones could be predicted in 73% by interictal spiking. However, not all ictal onset zones were predicted by the interictal spike focus, in particular if a patient presented with more than one ictal onset zone. Interestingly, a higher number of implanted electrodes and a higher number of recorded ictal onset zones may be related. Analysis of interictal subdural EEG may be helpful in the prediction of the ictal onset zone.,