Abstracts

Rationale: Patients with drug resistant epilepsy (DRE) may achieve seizure freedom with epilepsy surgery. The success of surgery depends on the identification and ablation/resection of the epileptogenic zone (EZ). Intracranial electroencephalography (iEEG) is regarded as the gold standards for recording of seizures and identification of the seizure onset zone, which offers the best approximation of the EZ. Yet, iEEG recordings are spatially limited and may lead to incomplete identification of the EZ and thus surgical failure. Noninvasive techniques, such as magnetoencephalography (MEG), may augment the presurgical evaluation and improve the surgical outcome of children with DRE. Here, we present seizure free outcome from a series of children with DRE that failed iEEG-guided surgery, and subsequently underwent MEG-guided surgery.

Methods: We retrospectively reviewed the medical records of children with DRE who underwent repeat epilepsy surgery at Cook Children’s Medical Center within the last 10 years. We identified six patients who had an initial iEEG-directed surgery with a follow-up Engel score ≥ 2 (one year after surgery) and a repeat surgery after re-evaluation with MEG with a follow-up Engel score 1 (one year after surgery). A realistic head model was constructed using each patient’s magnetic resonance imaging (MRI) obtained prior to the second surgery. Two independent readers identified interictal epileptiform discharges (IEDs) on MEG data (Figure 1), and localized the underlying generators of IEDs with equivalent current dipoles (ECDs) (goodness-of-fit ≥ 70%) and performed an in-house dipole clustering method (Figure 2A). Surgical volumes from the second surgeries were manually delineated on patients’ post-surgical MRIs. We then estimated the mean distance of ECD clusters from the two volumes and compared them with Wilcoxon signed rank test (statistical significance at p< 0.05).