Magnetoencephalography for Pediatric Epilepsy: How We Do It

Abstract

SUMMARY: Magnetoencephalography (MEG) is increasingly being used in the preoperative evaluation of pediatric patients with epilepsy. The ability to noninvasively localize ictal onset zones (IOZ) and their relationships to eloquent functional cortex allows the pediatric epilepsy team to more accurately assess the likelihood of postoperative seizure freedom, while more precisely prognosticating the potential functional deficits that may be expected from resective surgery. Confirmation of clinically suggested multifocality may result in a recommendation against resective surgery because the probability of seizure freedom will be low. Current paradigms for motor and somatosensory testing are robust. Paradigms allowing localization of those regions necessary for competent language function, though promising, are under continuous optimization. MR imaging white matter trajectory data, created from diffusion tensor imaging obtained in the same setting as the localization brain MR imaging, provide ancillary information regarding connectivity of the IOZ to sites of rapid secondary spread and the spatial relationship of the IOZ to functionally important white matter bundles, such as the corticospinal tracts. A collaborative effort between neuroradiology, neurology, neurosurgery, neuropsychology, technology, and physics ensures successful implementation of MEG within a pediatric epilepsy program.

Somatosensory Evoked Field in Response to Visuotactile Stimulation in 3- to 4-Year-Old Children

“…Under natural testing conditions this is especially challenging for preschoolers aged 2- to 5-years old, since children in this age group are generally less able to suppress movements and to follow procedural instructions (for a review see Pang, 2011). While substantial MEG research has been performed with sleeping or sedated preschoolers in clinical evaluation settings (e.g., Bercovici et al, 2008; Schwartz et al, 2008; Pihko et al, 2009), few studies so far have accomplished preschool MEG measurements under natural and awake testing conditions in an adult MEG system (Fujioka and Ross, 2008; Gaetz et al, 2010). …”

Past, Current and Future Clinical Applications of MEG

“…Due to this fact, the speed at which the scans can be performed has increased as knowledge about the most effective protocols grows. As confidence in the diagnostic abilities of the technique grows, more and more clinicians become aware of its utility, resulting in MEG being performed routinely at various epilepsy centres around the world, not as an an innovative and exploratory technique but as a valued and essential step in determining the most appropriate intervention (Ray & Bowyer, 2010;Schwartz et al, 2008). If other conditions are to use MEG as part of a routine diagnostic procedure, then it is necessary not only to apply standard analysis techniques, but to use studies of these conditions to drive forward novel and innovative statistical and modelling techniques.…”

Bioelectric Measurements: Magnetoencephalography

“…MEG source localization aids in selecting sites for grids to be used in subdural EEG recordings (Knowlton et al, 2009;Mamelak et al, 2002;Sutherling et al, 2008;Vitikainen et al, 2009). MEG can also encourage epilepsy surgery by demonstrating focal epileptiform activity, whereas traditional methods suggest multifocal activity or reveal bilateral, multifocal, or diffuse ictal onset, indicating an unfavorable candidate for epilepsy surgery (Schwartz et al, 2008). A high correlation of the resection volume with the brain region containing MEG source clusters of epileptic spikes predicts favorable outcome in epilepsy surgery (Fischer et al, 2005;Wilenius et al, 2013).…”