MEG Predicts Outcome Following Surgery for Intractable Epilepsy in Children with Normal or Nonfocal MRI Findings

Abstract

Summary:Purpose: To identify the predictors of postsurgical seizure freedom in children with refractory epilepsy and normal or nonfocal MRI findings.Methods: We analyzed 22 children with normal or subtle and nonfocal MRI findings, who underwent surgery for intractable epilepsy following extraoperative intracranial EEG. We compared clinical profiles, neurophysiological data (scalp EEG, magnetoencephalography (MEG) and intracranial EEG), completeness of surgical resection and pathology to postoperative seizure outcomes.Results: Seventeen children (77%) had a good postsurgical outcome (defined as Engel class IIIA or better), which included eight (36%) seizure-free children. All children with postsurgical seizure freedom had an MEG cluster in the final resection area. Postsurgical seizure freedom was obtained in none of the children who had bilateral MEG dipole clusters (3) or only scattered dipoles (1). All five children in whom ictal onset zones were confined to ≤5 adjacent intracranial electrodes achieved seizure freedom compared to three of 17 children with ictal onset zones that extended over >5 electrodes (p = 0.002). None of six children with more than one type of seizure became seizurefree, compared to eight of 16 children with a single seizure type (p = 0.04). Complete resection of the preoperatively localized epileptogenic zone resulted in seizure remission in 63% (5/8) and incomplete resections, in 21% (3/14) (p = 0.06). Age of onset, duration of epilepsy, number of lobes involved in resection, and pathology failed to correlate with seizure freedom.Conclusions: Surgery for intractable epilepsy in children with normal MRI findings provided good postsurgical outcomes in the majority of our patients. As well, restricted ictal onset zone predicted postoperative seizure freedom. Postoperative seizure freedom was less likely to occur in children with bilateral MEG dipole clusters or only scattered dipoles, multiple seizure types and incomplete resection of the proposed epileptogenic zone. Seizure freedom was most likely to occur when there was concordance between EEG and MEG localization and least likely to occur when these results were divergent.

Correlating magnetoencephalography to stereo-electroencephalography in patients undergoing epilepsy surgery

“…Some used geometric measures such as spike sources within 1 cm between adjacent sources (Mamelak et al, 2002;RamachandranNair et al, 2007;Almubarak et al, 2014). Some used anatomical measures such as SECDs located contiguously within neighbouring gyri (Oishi et al, 2006).…”

Fast oscillations associated with interictal spikes localize the epileptogenic zone in patients with partial epilepsy

“…Several studies have shown that this method can provide reliable and useful information in presurgical patients with partial epilepsy (Stefan et al, 2003;Wu et al, 2006;RamachandranNair et al, 2007), and have concluded that non-invasive MEG techniques might eventually partly replace invasive intracranial recording techniques (Pataraia et al, 2004;Papanicolaou et al, 2005;Knowlton et al, 2006). However, the analysis procedures require that each dipole is manually reviewed and classified as either corresponding to a real spike or as corresponding to a non-epileptic origin, which can be timeconsuming, requires trained and experienced scorers, and introduces a sizeable amount of subjectivity in the results.…”

Advances in neuroimaging in patients with epilepsy

“…In children with normal or subtle nonfocal MR imaging results, MEG findings have been found to predict surgical outcome. 101 In patients with recurrent seizures following unsuccessful epilepsy surgery, MEG has a role in localizing postsurgical epileptiform disturbances, 62 because MEG is less affected by the biophysical disturbances of cranial defects and brain volume changes. One of the limitations of MEG is in identifying epileptiform paroxysms from deep-seated areas such as the mesial temporal lobe.…”