High frequency oscillation networks and surgical outcome in adult focal epilepsy
To investigate whether high frequency oscillations (HFOs) show spatiotemporal propagation and assess the relevance of the earliest oscillations in relation to the seizure onset zone and postsurgical outcome.
We retrospectively investigated the intracerebral EEG of patients who became seizure free after subsequent surgery. We marked HFOs during one hour of recordings. We calculated the time delay between pairs of channels as the median delay between their HFOs, and constructed a time line of the delay of each channel with respect to the earliest channel (first source channel). A network was defined when a temporal order could be established among the channels based on the existence of statistically significant delays.
Fifteen patients with good surgical outcome were included. We found ripple networks in all patients, and fast ripple networks in 9. For ripples, first source channels were found in a higher proportion in the seizure onset zone than the rest of the network channels (15/27, 56% vs. 93/262, 35%; p=0.04). For both ripples and fast ripples, first source channels were resected more often that the rest of the network channels (Ripples: 13/27, 48% vs. 65/262, 25%; p=0.01. Fast ripples: 8/9, 89% vs. 17/40, 43%; p=0.002); channels with the highest rates of ripples and fast ripples were resected in a similar proportion.
These results demonstrate that interictal HFOs are organized in networks, and indicate a possible need for the resection of first source channels. However, resecting them is not superior to resecting channels with highest rates of HFOs.
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