Abstracts

Rationale: Scalp video EEG (SVEEG) often shows generalized spike-and-waves (GSW) in children with intractable focal epilepsy. Magnetoencephalography (MEG) can lateralize the spike dipoles of interictal GSW to assess surgical candidacy. Methods: We retrospectively identified children who had interictal GSW during non-REM sleep on SVEEG among the children who underwent MEG and intracranial video EEG (IVEEG) at The Hospital for Sick Children (Toronto, Canada). We analyzed interictal and ictal SVEEG, the lateralization/localization of MEG dipoles and extent of resection areas. Results: We retrospectively identified 28 children with interictal GSW during non-REM sleep on SVEEG among 103 children who underwent intracranial video EEG. During non-REM sleep, 21(75%) children had frequent interictal GSW, 6 intermittent and one rare. Twenty-three (82%) children had interictal focal discharges in addition to GSW. Lateralization of ictal SVEEG was concordant to the resective hemisphere in 15 (54%) children. Lateralized seizure semiology was concordant to the resective hemisphere in 11 (39%) children. Main seizure semiology consisted of partial seizures (9 children), periodic spasms (8), isolated epileptic spasms (2), tonic seizures (5), generalized tonic clonic seizures (2), myoclonic jerks (1) and atypical absence (1). Fifteen (54%) children had more than one seizure type. MEG dipoles in the resected hemisphere ranged from 7 to 151 (mean 64; 53-100%, mean 88%) comparing with those in contralateral hemispheres from 0 to 31 (mean 8). Cortical resections were performed over one lobe (2 children), 2 lobes (9), 3 (11), and 4 (3). The remaining 3 children did not undergo resective surgery due to overlapping ictal onset and functional zone. One and two lobe resection (11 children) included frontal lobe in all children, but no occipital lobe involvement. The remaining 14 children underwent multilobar resection including posterior quadrant. Conclusions: MEG can lateralize the source of interictal GSW in children with intractable focal epilepsy. Even when children show frequent interictal GSW during non-REM sleep and seizure semiology cannot be lateralized, they can still be considered for resective surgery if interictal focality on SVEEG and lateralized MEG dipoles are concordant. The resection areas, however, tend to be multi-lobar.