SURGERY for SEIZURES Volve Only the Anterior Two Thirds of the Corpus Callo- Sum Unless the Patient Has Severe Retardation

Home , Amygdalohippocampectomy, Epilepsy surgery, Wada test

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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 callosum unless the patient has severe retardation. For some JEROME ENGEL, JR., M.D., PH.D. localized cortical resections, however, intraoperative testing 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 disabling 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 before 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

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 tomography 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 seizures 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- ing with scalp and sphenoidal electrodes can provide FORMED PROCEDURE WORLDWIDE INDICATIONS false information about the origin of the seizures, in the

BEFORE 1985– past this procedure was often repeated with stereotacti- 1985† 1990‡ cally implanted depth electrodes, or subdural electrodes, Anterior temporal lobectomy 2336 4862 Medically refractory tempo- placed so as to record information directly from the pre- Amygdalohippocampectomy — 568 ral-lobe epilepsy sumed epileptogenic region.21 The use of structural and Neocortical resection 825 1073 Medically refractory partial functional neuroimaging to confirm location by nonin- seizures due to localized neocortical disturbances vasive ictal EEG has now eliminated the need for in- Lesionectomy — 440 Medically refractory partial tracranial recording in all but a few patients. Interictal Multiple subpial transections — — seizures originating in pri- positron-emission tomography was the first method of mary cortical areas functional neuroimaging found to be of value for this pur- Hemispherectomy and large 88 448 Medically refractory unilater- 23 multilobar resections al seizures associated with pose, but interictal — and particularly ictal — single- widespread hemispheric le- photon-emission computed tomography24 also provides sions and profound contralateral neurologic deficits important information that permits safe and effective Corpuscallosotomy 197 843 Medically refractory drop at- surgery without invasive monitoring. tacks as the most disabling Identifying the epileptogenic region is most difficult type of seizure in patients with so-called cryptogenic partial epilepsy, Total 3446 8234 in which no structural lesion has been found preopera- *Data were obtained from Engel et al.3 Dashes indicate that no data are available. tively. Marked improvements in high-resolution MRI, †Results reported for 39 epilepsy-surgery centers participating in the first International however, now permit visualization of hippocampal at- Palm Desert Conference in 1986. rophy in most patients who previously were given a di- ‡Results reported for 107 epilepsy surgery centers participating in the second International 25 Palm Desert Conference in 1992. agnosis of cryptogenic temporal-lobe epilepsy and of

Vol. 334 No. 10 CURRENT CONCEPTS 649

Age Group EEG Electroencephalogram Structural Functional at Surgery Leads Imaging Imaging

MRI PET

Mesial Adolescent Temporal-Lobe or Epilepsy young adult

MRI MRI

Discrete Neocortical Any age Lesion

MRI PET

Diffuse Infant or Hemispheric very young Disturbance child

Figure 1. Surgically Remediable Epileptic Syndromes Important diagnostic features of three surgically remediable syndromes are shown. Mesial temporal-lobe epilepsy (top panel) is char- acterized on EEG by focal interictal sphenoidal spikes (small arrows) and ictal onset (large arrow). Unilateral hippocampal atrophy

(arrow) is apparent on a T1-weighted coronal MRI. Axial positron-emission tomography (PET) reveals extensive unilateral temporal glucose hypometabolism (arrow). In the middle panel, EEG in a 23-year-old woman with a low-grade glioma (a discrete neocortical lesion) in the right inferior temporal– occipital junction showed focal interictal spikes (small arrow) and ictal onset (large arrow) in the right posterior temporal area. The structural lesion is evident on a T2-weighted coronal MRI through the temporal–occipital junction (arrow). Functional MRI of the re- sponse to visual stimulation indicated that the lesion did not encroach on primary visual cortex (an axial image is shown). In the bottom panel, EEG in a two-year-old child with catastrophic secondarily generalized seizures and unilateral seizures due to a left-sided hemimegaloencephaly (diffuse hemispheric disturbance) revealed attenuation over the left hemisphere (lower channels), widespread interictal spikes most prominent on the left side (small arrows), and a variety of ictal discharges emanating from the left side (a tonic seizure is shown, beginning at the large arrow). The patient also had a markedly dysplastic left hemisphere on MRI (the right side of the T1-weighted axial image) and, on functional PET, profound hypometabolism of glucose in the left hemisphere (right side of axial image), but an apparently normal pattern of glucose metabolism in the right hemisphere (left side of image). Illustration by Lynne Olson from material provided by Drs. John Curran, John Mazziotta, Michael Phelps, Raman Sankar, and Arthur Toga. focal, dysplastic, cortical lesions in many patients pre- ically refractory epilepsy. In practice, most patients viously given a diagnosis of cryptogenic neocortical epi- referred to epilepsy-surgery centers still have several sei- lepsy.26 Positron-emission tomography27 and MRI28 have zures a month — and sometimes several a day — despite also helped to identify localized, resectable, cortical ab- treatment with standard antiepileptic drugs, alone and in normalities in infants and young children with crypto- combination, at adequate doses. However, patients with genic forms of catastrophic secondary generalized epi- disabling but infrequent seizures can also benefit greatly lepsy, such as infantile spasms, who otherwise would from surgery, as can those for whom a doctor’s insist- not have been considered for surgery. Presurgical eval- ence on yet another drug regimen only delays a defini- uation may become cheaper because of new techniques tive surgical procedure and creates a risk that irrevers- for outpatient ictal EEG recording with digital home- ible psychosocial consequences of prolonged illness will monitoring systems,29 advances in the identification of develop. Surgical intervention need not be considered ictal, as well as interictal, spike sources by magnetoen- only as a last resort. There are surgically remediable syn- cephalography,30 and the more widespread use of mag- dromes (Fig. 1) — conditions with a known pathophys- netic resonance spectroscopy and functional MRI.25 iology and natural history that have a poor prognosis with purely medical treatment, but that respond well to EARLY INTERVENTION surgical treatment.3 Because patients with these condi- Timely identification of potential candidates for sur- tions can be readily identified by noninvasive studies, gery has suffered from the imprecise definition of med- and because these disorders can have progressive fea-

650 THE NEW ENGLAND JOURNAL OF MEDICINE March 7, 1996 tures, referral to an epilepsy-surgery center ought to be Table 3. The Syndrome of Mesial Temporal-Lobe Epilepsy.* considered as soon as first-line antiepileptic medications fail to be effective. For most conditions, this means high- History Higher incidence of complicated febrile convulsions than in other types of epi- dose carbamazepine and phenytoin. Continued attempts lepsy. to treat patients with second-line drugs, or combinations Family history of epilepsy common. Onset in latter half of first decade of life. of drugs, may not be in the best interest of those with Auras that often occur in isolation common. surgically remediable syndromes. Infrequent secondarily generalized seizures. The prototype of a surgically remediable syndrome is Seizures that often remit for several years until adolescence or early adulthood. 31 Seizures that often become medically intractable. mesial temporal-lobe epilepsy, which has a character- Interictal behavioral disturbances can develop, most commonly depression. istic presentation and a specific pathophysiologic basis: Clinical features of seizures hippocampal sclerosis (Table 3). This disorder is possi- An aura is usually present. The most common is epigastric, often with other au- bly the most common form of epilepsy and one of the tonomic or psychic symptoms, including emotion (e.g., fear). Olfactory or gus- most refractory to medical treatment. Seizures usually tatory sensations can occur. Auras usually last several seconds. Complex partial seizures often begin with arrest and stare; oroalimentary autom- begin in the first decade of life and characteristically be- atisms and complex automatisms are common. Posturing of one arm may oc- come intractable as early as adolescence. The risk of ir- cur contralateral to the ictal discharge. The seizure usually lasts one to two minutes. reversible psychosocial consequences for patients with The postictal phase usually includes disorientation, recent-memory deficit, am- intractable seizures is great. Most patients with this con- nesia for the event, and dysphasia if seizures begin in the language-dominant dition, however, can be easily identified as likely candi- hemisphere. This phase lasts several minutes. dates for surgery by anterior temporal interictal spikes Neurologic and laboratory features on EEG, hippocampal atrophy on high-resolution MRI, Neurologic examination usually normal except for memory deficit. Unilateral or bilateral independent anterior temporal EEG spikes with maximal and temporal-lobe hypometabolism noted on interictal amplitude in basal electrodes. positron-emission tomography. Ictal EEG, neuropsycho- Extracranial ictal EEG activity only with symptoms of complex partial seizure; logical tests, and if necessary, ictal single-photon-emis- usually initial or delayed focal rhythmic onset pattern of 5 to 7 per second, maximal amplitude in one basal temporal derivation. sion computed tomography can confirm the diagnosis, Usually temporal-lobe hypometabolism on interictal positron-emission tomogra- and anterior mesial temporal-lobe resection offers a 70 phy with fluorodeoxyglucose, often involving ipsilateral portion of the thalamus and basal ganglia. to 80 percent chance of cure. Usually temporal-lobe hypoperfusion on interictal single-photon-emission com- Patients with medically refractory partial seizures puted tomography and characteristic pattern of hyperperfusion and hypoper- that are due to discrete structural lesions, such as glial tu- fusion on ictal single-photon-emission computed tomography. Usually memory dysfunction specific to the involved temporal lobe on neuropsy- mors or congenital malformations, also have a surgically chological testing and amnesia with contralateral intracarotid injection of remediable syndrome. Caution should be exercised, how- amobarbital. ever, because some structural lesions are not clinically Hippocampal atrophy usually visible on MRI. important and others are part of a multifocal process in *Adapted from Engel.32 which another lesion that cannot be visualized is actually responsible for the epileptic condition.33 Consequent- ly, surgical treatment should not be undertaken on the iparesis with a useless hand, this surgical procedure in- basis of structural imaging alone; confirmation of epi- troduces no new motor deficit; in fact, function of the leptogenicity is necessary, and this usually requires ictal affected limbs often improves. Without surgery such EEG. Surgical outcomes in properly evaluated patients children might be condemned to life in an institution, but with discrete epileptogenic lesions are equivalent to those with appropriate surgical intervention they have a 60 to in patients treated for mesial temporal-lobe epilepsy. 80 percent chance of living a nearly normal life. Catastrophic seizures, either generalized or unilater- Patients with secondary generalized epilepsy, such as al, in infants and young children can result from a num- the Lennox–Gastaut syndrome, have diffuse brain dam- ber of brain disturbances that are confined to one, or part age and often have disabling drop attacks that cause fre- of one, hemisphere; these include hemimegaloenceph- quent severe injury. Antiepileptic drugs are usually inef- aly and other diffuse cortical dysplasias, Sturge–Weber fective against such seizures, and patients must therefore syndrome, large porencephalic cysts, and the usually wear protective helmets and greatly limit their activities. unilateral inflammatory process of Rasmussen’s enceph- If drop attacks are the most disabling type of seizure alitis.34 Medically refractory seizures in these conditions experienced by a patient with secondary generalized ep- often occur many times a day, are associated with pro- ilepsy, corpuscallosotomy should be considered.35 Cor- found developmental delay, and can be life-threatening. puscallosotomy can completely end drop attacks for a The pathologic region is easily identified with MRI or, large proportion of patients, but it is a palliative, not a in some cases, positron-emission tomography. Ictal EEG curative, procedure; it is not likely to affect other types can demonstrate that the epileptogenic abnormalities of seizures or to alter the mental retardation or other are restricted to the structurally abnormal hemisphere, neurologic abnormalities usually associated with second- and both EEG and positron-emission tomography can ary generalized epilepsy. Nevertheless, the tremendous be useful in confirming that the contralateral hemi- positive effect of this surgical intervention on the qual- sphere is functionally intact. In these situations, hemi- ity of life of patients with disabling drop attacks justifies spherectomy or a large multilobar resection can end ha- regarding this condition as surgically remediable. bitual seizures and reverse the inevitable developmental Advances in diagnostic technology and surgical pro- delay.34 Because removal of the perirolandic area is usu- cedures will undoubtedly result in the identification of ally considered only for patients who already have hem- more surgically remediable syndromes in the future. For

Vol. 334 No. 10 CURRENT CONCEPTS 651 instance, studies are under way to determine whether Table 4. Results of Surgical Treatment for Epilepsy, Worldwide, the progressive verbal agnosia that develops in children 1986–1990.* 36 with the Landau–Kleffner syndrome, presumably due NO. OF to cryptogenic epileptic activity involving language cor- SURGICAL PROCEDURE PATIENTS OUTCOME tex, can be reversed by multiple subpial transection that FREE OF WORTHWHILE NO WORTHWHILE eliminates epileptogenic activity in that area without in- SEIZURES† IMPROVEMENT‡ IMPROVEMENT troducing additional language disturbances. percent Patients with medically refractory seizures who clearly Temporal-lobe resection do not have one of the surgically remediable syndromes Anterior temporal 3579 67.9 24.0 8.1 mentioned here should be given more aggressive ther- lobectomy Amygdalohippo- 413 68.8 22.3 9.0 apy with antiepileptic drugs, alone or in combination. campectomy They should not, however, be discounted as possible Neocortical resection 805 45.1 35.2 19.8 candidates for surgery, and at some point referral to an Lesionectomy 293 66.6 21.5 11.9 epilepsy-surgery center is appropriate. Although these Hemispherectomy 190 67.4 21.1 11.6 patients often require prolonged and expensive invasive Multilobar resections 166 45.2 35.5 19.3 monitoring with depth electrodes or subdural electrodes, Corpuscallosotomy 563 7.6 60.9 31.4 and although fewer than 50 percent of patients who do *Results reported for 100 epilepsy-surgery centers at the second International Palm Desert not have a surgically remediable syndrome become sei- Conference in 1992. Data were obtained from Engel et al.37 †The patients had to be free of disabling seizures for at least two years. Some patients may zure-free postoperatively, most obtain some benefit. It is still have occasional auras. Patients take antiepileptic medication for at least two years post- important to make sure that patients do not have a sur- operatively and may elect to continue thereafter. ‡This was defined as more than a 90 percent reduction in the frequency of seizures. This gically remediable syndrome before delaying referral for category includes patients who may have had only one or two seizures since surgery. surgery and proceeding with numerous, prolonged ma- nipulations of medical therapy. formal testing but almost never noticed by patients SURGICAL OUTCOME themselves. Because memory function specific to the Table 4 shows data on the results of surgical treat- involved temporal lobe is usually depressed preopera- ment for epileptic seizures, during the period 1986 to tively, hippocampal resection is unlikely to introduce a 1990, as obtained from an international survey of 100 new deficit, and in fact, often results in an improvement epilepsy-surgery centers.37 These data do not fully re- in memory function specific to the contralateral tem- flect the success of current surgical techniques for two poral lobe. However, anteromesial temporal lobectomy reasons: some reporting centers were in developing coun- in the dominant hemisphere of patients with normal tries that did not have access to the most modern ap- memory will produce a deficit in verbal memory that proaches, and results in general have improved consid- could pose a problem for those who need to function erably in the past five years. Although no comparable at a high intellectual level. Functional mapping tech- worldwide data on outcomes are available for surgical niques, including the intracarotid amobarbital proce- procedures performed since 1990, the results reported in dure, can be used to predict when surgical intervention the more recent literature from individual centers, 38 as is likely to cause further language, memory, or other well as data presented at professional meetings, indicate neurologic disturbances and can enable surgical strate- steady progress. In attempting to gauge the cost effec- gy to be altered in order to avoid unacceptable conse- tiveness of surgery, however, the translation of the suc- quences. In some circumstances, however, new neurolog- cessful elimination of seizures into psychosocial reha- ic deficits are unavoidable and must be accepted by bilitation, elimination of disability, and improved quality patient and physician as a tolerable trade-off before of life becomes important.39,40 Although patients who no any surgery is undertaken. longer have seizures represent an important savings in Microsurgical techniques and other improvements in direct costs for medical care, they may still remain de- surgical methods have not only increased the safety pendent on family and the social-welfare system and and efficacy of routine surgical procedures for epileptic have many indirect costs associated with their disabili- seizures, but also made even hemispherectomy and cor- ty.41 Patients are most likely to be able to work and to puscallosotomy more attractive alternatives. Modifica- live relatively normal, productive lives if surgical inter- tions of hemispherectomy have almost eliminated the vention takes place early in the course of their epileptic devastating delayed complications previously associat- disorders. ed with the procedure.43 The ability to sever the corpus Operative complications of surgery for epileptic sei- callosum without entering the third ventricle has great- zures are rare42 and account for minimal disability. In ly improved the early postoperative course of patients localized resective surgery, less than 5 percent of pa- treated with that technique; section of only the anterior tients have some postoperative neurologic deficit due two thirds of the corpus callosum can avert the some- to unintended vascular compromise or other accidental times disturbing symptoms that arise from disconnect- damage to essential neural tissue; the great majority of ing the two hemispheres.44 these disturbances are transient and resolve within a period of months. Mesial temporal-lobe resections are FUTURE DIRECTIONS often associated with defects in the contralateral supe- New antiepileptic drugs will undoubtedly benefit some rior quadrant of the visual field that are identifiable by patients who now have medically refractory epilepsy,

652 THE NEW ENGLAND JOURNAL OF MEDICINE March 7, 1996

but pharmacologic advances are unlikely to decrease 19. Morrell F, Whisler WW, Bleck TP. Multiple subpial transection: a new ap- proach to the surgical treatment of focal epilepsy. J Neurosurg 1989;70:231-9. the large number of potential candidates for surgery in 20. Tuxhorn I, Holthausen H, Boenigk HE, eds. Paediatric epilepsy syndromes the near future. Stimulation of the vagus nerve 45 and the and other surgical treatment. London: John Libbey (in press). thalamus46 may reduce the frequency and severity of 21. Lüders HO, Engel J Jr, Munari C. General principles. In: Engel J Jr, ed. Sur- gical treatment of the epilepsies. 2nd ed. New York: Raven Press, 1993:137- some forms of epileptic seizures, but these techniques 53. remain experimental and the indications for their use 22. Engel J Jr, Burchfiel J, Ebersole J, et al. Long-term monitoring for epilepsy: report of an IFCN committee. Electroencephalogr Clin Neurophysiol 1993; are uncertain. 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