MEG Predicts Epileptic Zone in Lesional Extrahippocampal Epilepsy: 12 Pediatric Surgery Cases

Abstract

Summary:Purpose: To discover whether the spatial distribution of spike sources determined by magnetoencephalography (MEG) provides reliable information for planning surgery and predicting outcomes in pediatric patients with lesional extrahippocampal epilepsy.Methods: We retrospectively studied 12 children with extrahippocampal epilepsy secondary to cortical dysplasia (CD), tumor, or porencephalic cyst. We compared interictal MEG spike source locations and somatosensory evoked fields derived from equivalent-current dipole modeling with intraoperative or extraoperative electrocorticography (ECoG).Results: MEG spike sources were found in proximity to the lesion in all patients and extended from lesions in five patients with CD. Marginal spike sources were noted in three patients with tumors, one patient with a cyst, and one with CD, and extramarginal sources in three patients with tumors. Three patients with tumors underwent lesionectomy only; two had further cortical excisions. One patient with CD underwent lesionectomy only, three had lesionectomy and cortical excisions, and two had lesionectomy and multiple subpial transection. Asymmetric MEG spike sources correlated with ECoG findings in all patients. Residual epileptiform discharges on postexcisional ECoG corresponded to spike sources in three patients with tumors and one patient with a cyst. Eleven patients have been seizure free for 1-6 years (mean, 4 years). One patient had residual seizures after incomplete excision of right temporal CD.Conclusions: MEG delineated asymmetric epileptogenicity surrounding lesions and the eloquent cortex. Complete tumor resection produced favorable outcomes despite residual postexcisional ECoG spikes and extramarginal MEG spike sources. CD characterized by clusters of MEG spike sources within and extending from lesions seen on magnetic resonance imaging (MRI) should be removed to prevent seizures.

Refractory Nonlesional Neocortical Epilepsy: Current Trends

“…The contribution of MEG to surgical evaluation of both lesional epilepsy and NLNE is well established [58][59][60][61][62][63]. MEG often shows high concordance with iEEG, similar to that of SISCOM, and concordance between MEG and iEEG with normal MRI is associated with better outcomes of epilepsy surgery [55,[64][65][66].…”

The role of magnetoencephalography in epilepsy surgery

“…45 The utility of interictal MEG for localizing the epileptogenic zone has been demonstrated on the basis of postsurgical seizure freedom. 48,56,68 Magnetoencephalography has been used both in children with lesional epilepsy 48 and children with nonlesional epilepsy. 58 In cases of malformations of cortical development, the removal of both the MEG spike cluster and the MR imaging lesion are essential for favorable outcomes.…”

“…Magnetoencephalography has proven to be a valuable presurgical tool in identifying the epileptogenic zone and eloquent brain cortex, and in predicting surgical outcomes in a subset of children with intractable epilepsy. 27,28,48,55 An Overview of MEG Introduced in 1968, 9 MEG is a technique that allows for the measurement of extracranial magnetic fields generated by massive synchronized intraneuronal electric currents. Magnetoencephalography uses a "superconducting quantum interference device" (SQUID) 34,39 to amplify small magnetic fields generated by intracranial neuronal activity.…”

Utility of neuronavigation and neuromonitoring in epilepsy surgery

“…68 Slightly lower but substantial success is reported for normal or subtle nonfocal MR imaging findings, where MEG-guided resection for intractable epilepsy provided good seizure control in 17 of 22 children. 76 Indeed, in all 17 successfully treated patients there was an MEG cluster in the final resection area.…”