Epilepsy Surgery

Abstract

EpilepsiaVolume 44, Issue s6 p. 35-37 Free Access Epilepsy Surgery First published: 18 August 2003 https://doi.org/10.1046/j.1528-1157.44.s6.13.xCitations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Epilepsy surgery is defined as any neurosurgical intervention with the primary goal of relieving intractable epilepsy. Epilepsy surgery should abolish or reduce seizures, avoid neurologic or neuropsychological side effects, and improve the quality of life (1,2). The seizures of ∼25–30% of people with epilepsy cannot be controlled satisfactorily with antiepileptic drugs (AEDs), and many of these people can be cured by surgical intervention. Though exact epidemiologic data are lacking, it can be estimated that in Europe, with a population of the order of 730 million, ∼225,000–275,000 people are potential candidates for epilepsy surgery with an additional 14,000 people presenting each year (3,4). RECENT ADVANCES The current resurgence of interest in epilepsy surgery can be attributed to the factors listed (2). • Considerable technical advances have been achieved in presurgical evaluation using prolonged video-EEG monitoring, neuroimaging [magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), positron emission tomography (PET)] and other novel diagnostic techniques [magnetic resonance spectroscopy (MRS), functional MRI (fMRI), magnetoencephalography (MEG)]. The constant improvement of noninvasive techniques reduces the percentage of people with epilepsy needing invasive evaluation, which carries considerable risks and expense. • Surgical techniques have been improved (e.g., microneurosurgery, neuronavigation), and new procedures (e.g., selective amygdalohippocampectomy, multiple subpial transection) have been developed. • There have also been advances in presurgical evaluation. In addition, many teams complement the presurgical data by performing direct “acute” recordings on the exposed cortex during the operation (electrocorticography; ECoG). The practical impact of these short-duration recordings on the amount of cortex to be removed often remains unclear, but direct electrical stimulation of the cortex may be useful for sparing highly functional cortical areas (in unanaesthetised patients). In a number of patients, the precise topography and extent of the “epileptic zone” (the cortical area where ictal discharges originate) need invasive investigations for proper definition. There is a need, however, for an international consensus on interpretation of intracerebral and intracranial recordings. Chronically implanted intracranial subdural electrodes appear very useful for obtaining functional mapping of the cortex (e.g., speech areas, motor cortex) by electrical stimulation. Intracerebral electrodes may provide valuable information on the spatial and temporal organisation of intracerebral ictal discharges, and on the possible distribution of the sensorimotor pathways. • The natural history of various epileptic syndromes is better understood. Thus, surgically remediable syndromes such as mesial temporal lobe sclerosis with a reasonably reliable surgical prognosis, can be identified (5). • Various misconceptions about epilepsy surgery, which previously discouraged primary care physicians from referring people with epilepsy to specialist centres, have been corrected. • Epilepsy surgery is performed more and more in infants and young children with certain catastrophic epilepsies. A new understanding not only of the deleterious effects of frequently occurring seizures on the developing brain, but also of its considerable plasticity, has established paediatric epilepsy surgery as a major new field (6). PREOPERATIVE CRITERIA The conditions for preoperative assessment should be fulfilled before someone is considered a candidate for epilepsy surgery. • Principal indications for epilepsy surgery are represented by partial epilepsies. • The seizures must be medically refractory (see “Refractory Epilepsy,” pages 81–82); i.e., when satisfactory seizure control cannot be achieved with any of the potentially available effective antiepileptic drugs (AEDs), alone or in combination, at doses or levels not associated with unacceptable side effects (7). • The seizures must be disabling and significantly interfere with the person's quality of life including daily activities, education, employment or social contacts (see “General Considerations,” pages 57–58). The number and severity of seizures which are considered as disabling largely depend on the person's own perception. • The minimum disease duration before surgery is 2 years. • Special conditions apply for infants and children, especially for those with catastrophic epilepsies in whom the negative effects of frequent seizures on brain development have to be considered. Furthermore, the concept of disability cannot readily be applied to this population (1,3,8). TIMING The timing of epilepsy surgery is of crucial importance. People suffering from epileptic syndromes with a high probability of medical intractability and a favourable surgical prognosis (e.g., mesial temporal lobe epilepsy and certain lesional epilepsies) should be considered for surgery early. In these patients, continued unsuccessful treatment with AEDs carries a risk of the development of psychosocial consequences of prolonged illness, which are frequently irreversible even after otherwise successful surgery. Another argument for timely referral of people with surgically remediable syndromes to an epilepsy centre is the increasing evidence for a progressive nature of some epileptic syndromes or for possible complications related to the nature of the lesion (e.g., bleeding from cavernoma). Finally, the negative effects of seizures on the developing brain have to be given timely consideration (2). PRESURGICAL EVALUATION The success of epilepsy surgery depends on a thorough presurgical evaluation to identify the brain region generating the habitual seizures and to demonstrate that it can be removed safely without causing unacceptable neurologic or neuropsychological deficits. Presurgical assessment consists of a series of steps. • Medical history including a careful analysis of interictal and ictal symptoms to establish the diagnosis and classification of epilepsy. • Neuroimaging using high-resolution MRI to identify a possible structural lesion in relation to the patient's seizures. • Neurophysiological techniques and, specifically, video-EEG monitoring with scalp electrodes still represent the cornerstone of presurgical evaluation. During video-EEG monitoring, the epileptic nature of the patient's attacks can be proven and it can be established whether the patient suffers from a single or from multiple habitual seizure types. Clinical seizure symptoms provide valuable localising information. Whereas interictal EEG delineates the irritative zone, ictal EEG helps to identify the seizure onset zone. Invasive intracranial recordings have to be performed if noninvasive data are contradictory, and/or if a degree of precision is required, which cannot be obtained by noninvasive techniques. In special circumstances, ictal recordings may be unnecessary when sufficient evidence exists based on clinical seizure symptoms, interictal scalp-EEG, brain imaging, and neuropsychological data. The use of invasive techniques needs a careful risk–benefit calculation based on special expertise. Ancillary neurophysiologic techniques that may be used include evoked potential studies, cerebral functional mapping, MEG, ECoG, and magnetic stimulation. • Documentation of the functional deficit zone employing neuropsychological testing, interictal SPECT and/or PET, and the intracarotid sodium amytal test. • Careful assessment of the patient's psychiatric state, using psychiatric rating scales where appropriate (1,3,8). SURGICAL PROCEDURES Resective epilepsy surgery aims to remove that part of the brain where the seizures originate and to render the patient seizure free. Therefore, it can be considered as a potentially curative procedure. Alternative surgical techniques including disconnective surgery, (such as corpus callosotomy) and vagal nerve stimulation (see “Refractory Epilepsy,” pages 81–82), which are palliative procedures, should only be used if resective epilepsy surgery is impossible (1,2). OUTCOME The outcome of epilepsy surgery can be evaluated based on seizure control, neurologic and neuropsychological functioning, and quality of life. Depending on the underlying epilepsy syndrome, ∼70% of patients are rendered seizure free after resective epilepsy surgery. This percentage has to be contrasted with <5% of patients becoming seizure free after the administration of new AEDs. Refinement of neurosurgical techniques such as selective amygdalohippocampectomy helps to minimise verbal memory deficits after resections within the dominant temporal lobe. Psychosocial rehabilitation is becoming increasingly important after epilepsy surgery and should play a central role in the future. All these outcome parameters may change over time, necessitating a regular follow-up over prolonged periods. Outcome parameters can be correlated with preoperative data to provide exact prognostic information before surgery (2,3). QUALITY STANDARDS Because epilepsy surgery is an elective procedure, the quality standards have to be particularly high and stringently enforced. Epilepsy surgery—similar to transplant surgery—requires close collaboration of a multidisciplinary team of highly trained and experienced specialists including neurologists, neurosurgeons, neurophysiologists, neuropaediatricians, neuropsychologists, pathologists, and neuroradiologists as well as EEG technicians. Therefore, it should only be performed in a designated epilepsy centre with the appropriate personnel and technical conditions. Quality standards both for the technical and personnel aspects of an epilepsy centre have been proposed recently. These include the availability of an interdisciplinary core team with special expertise, 25 epilepsy operations per centre per year, an intensive monitoring unit combined with a neurosurgical department, regular follow-up investigations over long time periods and expertise in recognising when invasive recordings are necessary (1,9). Despite these considerable advances, there is still a tremendous mismatch between the large number of patients who would benefit from epilepsy surgery and the relatively small number of patients actually treated. It therefore seems that there is a moral obligation to make this potential curative procedure available to people suffering from disabling epilepsy. Because epilepsy surgery is still in an initial stage in many countries, the establishment of minimum standards for training of medical personnel and for technical facilities would allow new groups to work in this field. A European working group could eventually publish a list of European epilepsy centres including reference and basic centres and indicating in detail which presurgical evaluation and surgical procedures are available in a given centre. This would certainly improve the availability and quality of care for epilepsy patients in Europe (1). RECOMMENDATION Epilepsy surgery is potentially curative and should be made more widely available to the large number of people with disabling epilepsy who could benefit from it, especially children. REFERENCES 1 European Federation of Neurological Societies Task Force: presurgical evaluation for epilepsy surgery: European standards. Eur J Neurol 2000;7:119–22. 2 Engel J Jr. Surgery for seizures. N Engl J Med 1996; 334: 647– 52. 3 Engel J Jr. Surgical treatment of the epilepsies, 2nd ed. New York: Raven Press, 1993. 4 NIH Consensus Panel. Surgery for epilepsy: National Institute of Health Consensus Conference. JAMA 1990;264:729–33. 5 Wieser HG, Engel J Jr, Williamson PD, et al. Surgically remediable temporal lobe syndromes. In: J Engel, ed. Surgical treatment of the epilepsies. 2nd ed. New York: Raven Press, 1993: 49– 63. 6 Tuxhorn I, Holthausen H, Boenigk HE. Paediatric epilepsy syndromes and other surgical treatment. London: John Libbey, 1997. 7 Bourgeois B. General concepts of medical intractability. In: HO Luders, ed. Epilepsy surgery. New York: Raven Press, 1991: 77– 81. 8 Lüders HO. Epilepsy surgery. New York: Raven Press, 1992. 9 Binnie CD, Polkey CE. Commission on Neurosurgery of the International League Against Epilepsy, ILAE, 1993–1997. Epilepsia 2000; 41: 1346– 9. Citing Literature Volume44, Issues6September 2003Pages 35-37 ReferencesRelatedInformation