Identifying the Primary Epileptogenic Hemisphere from Electroencephalographic (EEG) and Magnetoencephalographic Dipole Lateralizations in Children With Intractable Epilepsy

Abstract

We used electroencephalographic (EEG) and magnetoencephalographic dipole lateralizations to identify the primary epileptogenic hemisphere in 41 children with intractable localization-related epilepsy. We compared EEG and magnetoencephalographic dipole lateralizations, EEG ictal onsets, and magnetic resonance images (MRIs). Concordant lateralization of EEG and magnetoencephalographic dipoles (> 50% of each lateralizing to the same hemisphere) occurred in 34 patients, with EEG ictal onsets in the same hemisphere in 23 (68%) and concordant MRI lesions in 23 (68%). Focal resection in 16 of 20 patients resulted in a good surgical outcome. Of the seven children with nonconcordant magnetoencephalographic and EEG lateralizations, one (14%) had EEG ictal onset and one (14%) had MRI lesions that lateralized; none had surgery. The relationship between lateralized EEG and magnetoencephalographic dipoles forecasts surgical candidacy. Concordant lateralizations predict good seizure control after surgery by identifying the primary epileptogenic hemisphere. Discordant lateralizations signify an undetermined epileptogenic hemisphere and contraindicate surgery without further testing.

Magnetoencephalography in Pediatric Lesional Epilepsy Surgery

“…Localization was also satisfactory at the level of the anatomical region because the MEG spike sources were distributed exactly at or in the vicinity of the lesion in most patients. The hemispheric lateralization rate is similar to or higher than that reported for patients with intractable focal epilepsy in previous studies: 68% (when compared to brain MRI and intracranial ictal onset zone) (12), 82% (lobar concordance to anatomical lesional in brain MRI) (7), and 89% (when compared to the final surgical decision) (4). The lobar or regional localization rate is similar to the 72% rate reported in patients with intractable focal epilepsy (7).…”

“…Removal of the dysplastic cortex that has not been characterized by brain imaging but by MEG was required for complete seizure freedom (13). In cases of discordant presurgical evaluation, concordant lateralization was related to good seizure control (12). Multiple MEG spike source clusters required identification of the multiple or extensive epileptogenic zone prior to accurate localization and delineation of the resection margin (21).…”

Surgical approaches to epilepsy

“…In our unit, we use a combination of MEG, and ictal and interictal video EEG to assist in the localization of the epileptogenic zone. Concordance between the scalp video EEG and MEG findings provides strong noninvasive evidence that surgical resection will be successful [9].…”

Epilepsy Surgery in Children: Why, When and How?

“…In a recent study, brain PET was also found to be a useful predictor of seizure outcome after hemispherectomy, bilateral PET abnormalities being associated with post-operative seizure recurrence [6]. Successful use of ictal SPECT for early seizure propagation [43][44][45], Magnetoencephalography (MEG) for source localization of interictal spikes [46,47] and mapping of language and motor function with functional MRI (fMRI) [48,49] are increasingly been reported. However, it remains to be seen if these techniques will independently expand the selection of pediatric surgical candidates, obviate the need for long-term invasive video EEG recordings, and improve the long term surgical outcome in children.…”