Noninvasive Mapping of Ripple Onset Predicts Outcome in Epilepsy Surgery.

OBJECTIVE Intracranial EEG (icEEG) studies show that interictal ripples propagate across the brain of children with medically refractory epilepsy (MRE) and the onset of this propagation (ripple-onset-zone, ROZ) estimates the epileptogenic zone. It is still unknown whether we can map this propagation non-invasively. The goal of this study is to map ripples (ripple-zone, RZ) and their propagation onset (ROZ) using high-density EEG (HD-EEG) and magnetoencephalography (MEG), and to estimate their prognostic value in pediatric epilepsy surgery. METHODS We retrospectively analyzed simultaneous HD-EEG and MEG data from 28 children with MRE who underwent icEEG and epilepsy surgery. Using electric and magnetic source imaging, we estimated virtual sensors (VSs) at brain locations that matched the icEEG implantation. We detected ripples on VSs, defined virtual-RZ and virtual-ROZ, and estimated their distance from icEEG. We assessed the predictive value of resecting virtual-RZ and virtual-ROZ for postsurgical outcome. Interictal spike localization on HD-EEG and MEG was also performed and compared with ripples. RESULTS We mapped ripple propagation in all patients with HD-EEG and in 27 (96%) patients with MEG. The distance from icEEG did not differ between HD-EEG and MEG when mapping the RZ (26-27 mm; p = 0.6) or ROZ (22-24 mm; p = 0.4). Resecting the virtual-ROZ, but not virtual-RZ or the sources of spikes, was associated with good outcome for HD-EEG (p = 0.016) and MEG (p = 0.047). INTERPRETATION HD-EEG and MEG can map interictal ripples and their propagation onset (virtual-ROZ). Mapping non-invasively the ripple onset may augment epilepsy surgery planning and improve surgical outcome of children with MRE. This article is protected by copyright. All rights reserved.