Incomplete resection of the icEEG seizure onset zone is not associated with post-surgical outcomes

TL;DR

This study shows that incomplete resection of seizure onset zones identified by icEEG does not necessarily lead to worse surgical outcomes, suggesting other mechanisms influence seizure recurrence.

Contribution

It provides evidence that complete resection of seizure onset zones is not essential for seizure freedom, challenging previous assumptions.

Findings

Most seizure onset regions are at least partially resected.

No significant association between extent of resection and seizure control.

Seizure recurrence may involve network mechanisms beyond onset zones.

Abstract

Delineation of seizure onset regions from EEG is important for effective surgical workup. However, it is unknown if their complete resection is required for seizure freedom, or in other words, if post-surgical seizure recurrence is due to incomplete removal of the seizure onset regions. Retrospective analysis of icEEG recordings from 63 subjects (735 seizures) identified seizure onset regions through visual inspection and algorithmic delineation. We analysed resection of onset regions and correlated this with post-surgical seizure control. Most subjects had over half of onset regions resected (70.7% and 60.5% of subjects for visual and algorithmic methods, respectively). In investigating spatial extent of onset or resection, and presence of diffuse onsets, we found no substantial evidence of association with post-surgical seizure control (all AUC<0.7, p>0.05). Seizure onset regions tends to be at least partially resected, however a less complete resection is not associated with worse post-surgical outcome. We conclude that seizure recurrence after epilepsy surgery is not necessarily a result of failing to completely resect the seizure onset zone, as defined by icEEG. Other network mechanisms must be involved, which are not limited to seizure onset regions alone.