Vol. 334 No. 10 CURRENT CONCEPTS 647 REVIEW ARTICLE partial removal and partial disconnection of affected tissue; these and related techniques are designed to re- CURRENT CONCEPTS duce movement of the remaining portions of the brain within the cranial vault and to ensure resorption of cer- ebrospinal fluid. Corpuscallosotomies now usually in- SURGERY FOR SEIZURES volve only the anterior two thirds of the corpus callo- sum unless the patient has severe retardation. For some JEROME ENGEL, JR., M.D., PH.D. localized cortical resections, however, intraoperative test- ing may be necessary, which prolongs the operation and occasionally requires the patient to be briefly awakened F the approximately 2 million Americans with a from anesthesia. New techniques for treating epilep- O diagnosis of epilepsy who are treated with antiep- togenic regions within primary cortical areas, such as ileptic drugs, 20 percent continue to have seizures 1; this those controlling language and motor function, include group of patients accounts for over 75 percent of the the removal of a discrete lesion without disturbing the cost of epilepsy in the United States. 2 For many of those adjacent cortex (lesionectomy) and multiple subpial tran- with medically refractory epilepsy, their disability can sections, which sever intracortical connections in a way be completely eliminated by surgical intervention. Only that prevents the spread of epilepsy and still preserves a small percentage of potential surgical candidates, how- the columnar structure necessary to maintain normal ever, are currently referred to epilepsy-surgery centers. 3 cortical function.19 The current resurgence of interest in surgery for epi- OVERVIEW lepsy can be attributed largely to technical advances in The classic 1886 paper of Victor Horsley4 heralded video EEG monitoring and neuroimaging, improvements the modern era of epilepsy surgery, and the introduc- in surgical technique, and a better understanding of the tion of electroencephalography (EEG) in the first half anatomical and pathophysiologic bases of the sympto- of this century provided a practical means for localizing matic epilepsies. Another factor is the correction of a va- epileptogenic abnormalities for resection.5,6 Neverthe- riety of misconceptions that have discouraged primary less, only a handful of epilepsy-surgery centers were cre- care physicians from referring patients for surgery in the ated, treating relatively few patients — and only one past. Finally, a clearer delineation of the natural history book on the subject appeared7 — before 1986, when a of certain catastrophic epileptic disorders of infants and series of international conferences and textbooks began young children and a new understanding of the plasticity to reflect an explosion of interest in the field. 8-18 By of the developing brain and the damage that seizures do 1992, over 100 epilepsy-surgery centers throughout the to it, as well as the improvements in diagnostic and sur- world offered a wide selection of surgical procedures gical technique, have created a major new field, pediatric (Table 1) to an increasing number of patients, ranging epilepsy surgery.20 from infants to senior citizens, for the treatment of dis- abling partial, and even generalized, seizures refractory PRESURGICAL EVALUATION to medical therapy.17 The optimal surgical intervention for epilepsy should Modern epilepsy surgery, like heart-transplant sur- destroy just enough neuronal tissue to eliminate seizures gery, requires a multidisciplinary team of highly trained and no more. Therefore, the objective of presurgical eval- and experienced specialists working together in an ep- uation is to identify the area of brain most responsible ilepsy center. A variety of surgical interventions are now for generating habitual seizures and to demonstrate that performed, usually with the patient under general anes- it can be removed without causing additional unaccept- thesia, according to the location and nature of the epi- able neurologic or cognitive deficits. There is no simple leptogenic abnormality. The majority of procedures re- test to delineate the epileptogenic zone, defined as the quire only a few hours in the operating room and a few volume of brain tissue necessary and sufficient for the days of postoperative hospital care. The most common generation of seizures. The boundaries of the epilepto- surgery consists of removal of the amygdala and ante- genic zone can only be approximated by identifying ar- rior part of the hippocampus and entorhinal cortex, as eas of the brain marked by persistent dysfunction, both well as a small portion of the temporal pole, leaving the epileptic and nonepileptic. A variety of diagnostic tests lateral temporal neocortex intact. New techniques for are used for this purpose (Table 2), but there is no con- hemispherectomy and multilobar resection involve the sensus on how much information is actually needed be- fore a particular surgical intervention can be recom- From the Departments of Neurology and Neurobiology and the Brain Re- mended.21 In most cases, presurgical evaluation involves search Institute, UCLA School of Medicine, Los Angeles. Address reprint re- quests to Dr. Engel at the Reed Neurological Research Ctr., 710 Westwood Plaza, tests that localize epileptic excitability with interictal Los Angeles, CA 90095-1769. EEG as well as long-term video EEG monitoring de- Supported in part by grants (NS-02808, NS-15654, NS-33310, and GM- signed to capture and characterize ictal electrical activ- 24839) from the National Institutes of Health and a contract (DE-AC03-76- SF00012) with the Department of Energy. ity and clinical symptoms; imaging studies, usually mag- 1996, Massachusetts Medical Society. netic resonance imaging (MRI), that indicate structural Downloaded from www.nejm.org at UAB LISTER HILL LIB on September 29, 2003. Copyright © 1996 Massachusetts Medical Society. All rights reserved. 648 THE NEW ENGLAND JOURNAL OF MEDICINE March 7, 1996 abnormalities; tests for nonepileptic dysfunction, includ- Table 2. Diagnostic Tests Used in Evaluation for ing positron-emission tomography to reveal areas of ab- Surgery for Epilepsy. normal glucose use, single-photon-emission computed to- mography to reveal areas of abnormal blood flow, and Tests of epileptic excitability Noninvasive EEG neuropsychological testing; and studies of normal corti- Routine interictal EEG cal function to determine areas that must be preserved Video EEG, long-term monitoring Outpatient long-term monitoring during surgery. This last category includes cortical map- Invasive EEG ping and intracarotid injection of amobarbital (the Wada Intraoperative electrocorticography test) to identify the language-dominant hemisphere and Stereotactic-depth-electrode, long-term recording Subdural grid or strip, long-term recording the laterality of memory function. Ictal single-photon-emission computed tomography Diagnostic strategy is currently tailored to the specif- Interictal and ictal magnetoencephalography* ic surgical intervention to be used.21 For standardized Functional MRI* temporal-lobe resections, the presurgical evaluation need Tests for structural abnormalities only determine that habitual seizures are originating X-ray films, computed tomography, and other radiographic studies within the boundaries of the intended excision and that MRI the structures of the contralateral mesial temporal lobe Magnetic resonance spectroscopy* can support memory. For specific neocortical resections Tests of functional deficit and multiple subpial cortical transections, more detailed Interictal positron-emission tomography Interictal single-photon-emission computed tomography investigation is required to identify the boundaries of Neuropsychological batteries the epileptogenic zone, as well as of adjacent areas of Intracarotid amobarbital (the Wada test) essential primary cortex. For hemispherectomies and Interictal EEG Interictal magnetoencephalography* large multilobar resections, the goal of the presurgical Magnetic resonance spectroscopy* evaluation is to determine the extent of the functional Tests of normal cortical function (cortical mapping) and structural disturbance of the involved hemisphere Intraoperative electrocorticography and whether the contralateral hemisphere is reasonably Extraoperative subdural-grid recording intact. If section of the corpus callosum is contemplat- Intracarotid amobarbital (the Wada test) Positron-emission tomography* ed, there must be a documented history of disabling drop Magnetoencephalography* attacks as the principal type of seizure; it is also impor- Functional MRI* tant to determine that the patients are not candidates for a more definitive resection. Before lesionectomy is *Still considered experimental. performed, it is necessary only to demonstrate that sei- zures are originating at the site of the structural lesion formed on an inpatient basis at most centers before any and that the lesion is in an essential cortical area that surgical treatment for epilepsy, in order to verify that cannot be resected. the events are epileptic, characterize the seizure semi- Long-term video EEG monitoring is generally per- ology, and if possible, identify electrographically the site of ictal onset.22 Several days of continuous monitoring is often required in order to record a sufficient number Table 1. Surgical Procedures Commonly Performed to Treat Epilepsy.* of seizures, thus making this the most expensive part of presurgical evaluation. Because noninvasive monitor- NO. PER-