The Use and Impact of Positron Computed Tomography Scanning in Epilepsy

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Abstract
Through the effective combination of instrumentation, tracer kinetic principles, and radiopharmaceuticals, positron computed tomography (PET) allows for the analytic, noninvasive measurement of local tissue physiology in humans. A large number of studies have already been performed in patients with epilepsy using 18F-fluorodeoxyglucose (FDG) to measure local cerebral glucose utilization. In patients with complex partial epilepsy who are candidates for surgery, hypometabolic zones have been seen consistently (70%) in the interictal state. These areas of hypometabolism have been related to electroencephalographic findings, surgical pathology, and clinical symptomatology. The complex anatomical and pathophysiological investigation of these hypometabolic zones is discussed. Ictal studies of patients with partial seizures have demonstrated a much more variable metabolic pattern which usually consists of hypermetabolism relative to baseline or interictal studies. Generalized epilepsy produced by electroconvulsive shock and petit mal epilepsy have been studied using FDG to estimate glucose metabolism. These studies demonstrated hypermetabolism in the ictal state, relative to interictal or postictal scans, but with a more generalized pattern than ictal studies of partial seizures. Methodological problems in the study of epilepsy with PET are discussed in detail. The investigation of interictal hypometabolism through animal models of epilepsy and quantitative autoradiography is described as a means to understand the human PET results. The impact and future direction of PET studies in epileptic populations will probably employ the use of behavioral, pharmacological, and electrophysiological maneuvers to provide more specific details about the fundamental pathophysiological mechanisms of specific aspects of epilepsy. These techniques may allow for a truly pathophysiological classification system for the common and unusual types of epilepsy, and through this classification system improve the therapeutic and prognostic clinical approach to patients.