Integration of EEG, MRI, and SPECT in Localizing the Seizure Focus for Epilepsy Surgery

Abstract

Summary: Several modalities are now available for detecting the structural and the functional abnormalities of a seizure focus. This article discusses the principles and techniques that can be used to integrate the data derived from different test modalities in delineating the seizure focus in epilepsy surgery candidates. An approach in integrating EEG, MRI, and SPECT abnormalities is described to demonstrate how the spatial relationships among them can be precisely determined by coregistering images of the abnormalities on the MRI. The recently developed technique of subtraction ictal SPECT coregistered to MRI (SISCOM) can reveal a discrete hyperperfusion focus with its relationship to the cerebral anatomy. The SISCOM focus can also serve as a target for intracranial electrode implantation and for subsequent surgical resection. This can be achieved by using a computer-based system of relating the image space to the surgical field. The limitations of each test in localizing the surgical seizure focus must be recognized when the value of each test is interpreted relative to those of other tests. In many patients, not all tests will show localizing abnormalities, and the foci determined by different tests may be incongruent. When the location of the focus is not compatible with the possible origin of the patient's habitual seizures, further evaluation with other tests, including intracranial EEG recordings, is necessary. The decision in determining which tests and how many to employ for localizing the surgical focus must be individualized for each patient. Key Words: EEG-MRI-SPECT-SISCOM-SeizurefociSurgical Planning.The success of focal epilepsy surgery strongly depends on accurate identification of the seizure focus. In their early pioneering work in epilepsy surgery, Sir Victor Horsley and Hughlings Jackson relied on their clinical observations and intraoperative examination to infer the location of the seizure focus for surgery (1). Since then, a number of technological advances have been made and have been used for identification of the potentially epileptogenic tissue for surgical resection. Modern technological modalities now utilized in localizing the surgical seizure focus include electrophysiology (EEG), cerebral structural imaging (MRI and magnetic resonance spectroscopy), cerebral function imaging (SPECT and PET), and magnetoencephalography (MEG). This article examines and discusses how EEG relates to the other modalities when used for evaluation of patients for focal epilepsy surgery. The technology of SPECT is used to demonstrate an approach of integrating the electrophysiologic, structural, and functional data derived from the presurgical evaluation of intractable epilepsy patients. ELECTROENCEPHALOGRAPHY Interictal EEGInterictal EEG is a safe and widely available tool for evaluating the extent and location of the seizure focus. With the advent of modern neuroimaging and of longterm video-EEG monitoring, interictal EEG recording remains an important localizing and prognostic tool in epilepsy surgery...

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