Electroencephalography as a Localizing Tool

Abstract

1. The immature brain is not a miniature adult brain, and adult-epilepsy concepts and protocols do not necessarily apply to infant-epilepsy surgery. 2. The epileptogenic zone is conceptually, and often also topographically, distinct from both the ictal-onset zone and the irritative zone (interictal spiking). This distinction is especially important in pediatric evaluations. 3. In partial seizure disorders, the best strategy at present for demarcating the epileptogenic zone seems to be a weighted confluence of an epileptogenic lesion (if present), the ictal-onset zone, and the irritative zone. If these zones are not perfectly convergent (as is usually the case), they are given relative weights according to individual patient factors and variations in philosophy among epilepsy centers. This approach leaves much to be desired, especially in extratemporal nonlesional cases; it is hoped that future research will identify more reliable interictal markers for the epileptogenic zone. 4. Some cases of catastrophic generalized epilepsies or multifocal independent partial seizures are due to localized pathology (ZCA) and respond to resection of the offending lesion (often multilobar or hemispheric). In this context, the epileptogenic zone is coincident with the epileptogenic lesion and is best demarcated by the confluence of interictal indicators of structural pathology. The most reliable localizing aspects of the EEG are, therefore, interictal nonepileptiform abnormalities traditionally associated with structural lesions.