Neuroimaging in Epilepsy

Abstract

Epilepsy represents a multifaceted group of disorders primarily divided into two broad categories: focal and generalized, though the dichotomy of generalized and focal epilepsies is somewhat indistinct. Some epilepsies may have focal lesions causing generalized seizures (e.g., West syndrome) while some generalized epilepsies may have focal seizures (e.g., Dravet syndrome). Generally, neuroimaging plays a crucial role in patients with suspected structural/metabolic or unknown causes of epilepsy. However, neuroimaging may not be warranted in certain generalized epilepsy syndromes (e.g., childhood or juvenile absence epilepsy; juvenile myoclonic epilepsy) or focal epilepsy syndromes (e.g., benign rolandic epilepsy, benign occipital epilepsy, Panayiotopoulas syndrome). The armamentarium of neuroimaging is becoming increasingly versatile. Advances in both structural neuroimaging such as computed axial tomography (CAT) or magnetic resonance imaging (MRI) and functional neuroimaging techniques have helped us characterize and understand epilepsy networks in patients with seizure disorders. Neuroimaging remains an important diagnostic tool for clinicians in determining the etiology of seizures, classifying epilepsy syndromes, and developing treatment strategies. Advanced neuroimaging techniques such as single-photon emission computerized tomography (SPECT), positron emission tomography (PET), magnetic resonance spectroscopy (MRS), magnetoencephalogram (MEG), and magnetic source imaging (MSI) can be very helpful in delineating the epileptogenic zone especially when clinical, structural MRI, scalp electroencephalogram (EEG), and/or video EEG data are discordant. Functional MRI (fMRI) identifies hemodynamic changes during task performance and identifies eloquent motor, sensory, language, and visual cortices. Diffusion tensor imaging (DTI) is another noninvasive way of understanding structural connectivity and macroscopic axonal reorganization of the brain. It is beyond the scope of this chapter to cover all new neuroimaging techniques used in patients with epilepsy, but we have attempted to illustrate common etiologies of epilepsies and their neuroimaging correlates for the purpose of Epilepsy Board review.