Presurgical MEG to forecast pediatric cortical epilepsies

Abstract

Although multiple modalities (semiology, EEG, MEG, PET, SPECT, fMRI) are useful for presurgical evaluation of patients with medication resistant epilepsy, only EEG and MEG have the millisecond time resolution to track the onset and spread of interictal discharges and ictal events. For good surgical outcome, both seizure onset zones (SOZ) and regions of immediate spread, the epileptogenic zone (EZ), need to be resected. Although for adults the main preoperative question may be whether seizures arise in left or right mesial temporal lobe, the locations of SOZ can be much more variable in children and adolescents. Recent studies indicate the most common cause of medically intractable epilepsy in pediatrics is cortical dysplasias functioning as epileptogenic regions. A child may have a single circumscribed cortical dysplastic region, multiple regions throughout a lobe, cerebral hemisphere, or even bihemispheric dysplastic regions. Sometimes seizures will start at just one focal cortical dysplastic region and spread throughout the brain. For other patients, multiple cortical dysplastic regions may independently generate seizures, more in the context of a seizure network than a single seizure focus. The difficult task is to anticipate the pattern of locations of cortical dysplasias and functional epileptogenic regions for each pediatric patient. Addressing this task adequately presurgically for each patient allows intracranial electrodes to be placed correctly to verify the locations where seizures start and to observe how the seizures spread in a single patient during different clinical seizure patterns. MEG with mathematical models of the head, brain and current source regions may be able to contribute significantly to the presurgical identification of the pediatric patient's seizure networks and to the prediction of source locations that should be assessed with intracranial EEG recording.