Neuroimaging in epilepsy

Major advancements in neuroimaging in epilepsy during the past decades have led to dramatic improvements of the clinical evaluation and management of patients with epilepsy. In epilepsy surgery evaluation of medically refractory cases, both functional and structural neuroimaging have contributed to improved localization and delineation of the epileptogenic focus. The development of high resolution magnetic resonance imaging (MRI) increases the detection rates of focal structural lesions, such as hippocampal sclerosis and cortical developmental malformations, in symptomatic localization-related epilepsy syndromes. Diffusion tensor imaging (DTI), tractography and functional MRI (fMRI) have been used increasingly to map the vital motor and sensory white matter fiber tracts and eloquent cortex, respectively, that need to be spared during epilepsy surgery, thereby minimizing postoperative neurologic deficits. Functional neuroimaging modalities including interictal positron emission tomography (PET) and ictal single photon emission computed tomography (SPECT) scanning have revolutionized our approach in different pediatric as well as adult epilepsy syndromes especially in MRI-negative cases. PET scanning using various tracers has assumed an important role in the identification of epileptogenic focus in cryptogenic cases and in certain syndromes which were previously thought to be non-amenable to cortical resection. Glucose metabolism PET can also evaluate the functional integrity of brain regions outside the epileptogenic zone as well as in the contralateral hemisphere; thereby, providing useful prognostic information. The advent of multimodality neuroimaging enables more precise guidance in the delineation of the epileptic focus to be resected while preserving eloquent cortex, thus improving the outcome of resective epilepsy surgery. Both structural and functional neuroimaging have been utilized as research tools to expand our knowledge and understanding of the underlying neurologic substrates and pathomechanisms of various epilepsy syndromes. In this chapter, we review the evolution of different neuroimaging modalities utilized in the past several decades in the assessment of epilepsy. We discuss the advances of both structural and functional neuroimaging highlighting their application in the presurgical evaluation of medically refractory epilepsy. We also discuss how these advances have expanded our knowledge of the pathomechanisms of epilepsy.