Surgical Treatment
In the last decade, considerable work has been dedicated to epilepsy surgery in young patients. At least in specialized centers, epilepsy surgery in children is no longer considered a treatment of last resort when all else has failed. Although an overwhelming majority of children are still treated with drugs, many with satisfactory results, and a few more can benefit from various nondrug therapies (see previous chapters), surgery is being increasingly used for patients resistant to medical treatment. Its indications, techniques, and results have received considerable attention (Lüders and Comair, 2001; Bureau et al., 1998; Tuxhorn et al., 1997a; Engel, 1993).
Surgical treatment is still used for only a relatively small proportion of children with difficult-to-control seizures. The usual delay from the onset of seizure intractability to surgery is still in the range of 12 to 15 years at most centers (Wyllie and Bingaman, 2001). The lack of a sufficient number of specialized epilepsy centers has also resulted in unacceptable delays. This may prove harmful, particularly for children who could benefit from the early elimination of or significant reduction in their seizures, which would result in better social integration. Physicians must be aware of the new concepts and techniques that allow the earlier safe use of surgical therapy for children with epilepsy.
The spectrum of surgical possibilities for early onset epilepsy has rapidly widened to include not only the focal epilepsies but also more diffuse types or specific etiologies. New categories of patients who might benefit from surgical methods have been identified (Duchowny, 1999; Engel and Shewmon, 1992). The small number of persons with epilepsy currently undergoing surgical treatment could increase considerably, even though a significant proportion (12% to 25%) present with types of secondary generalized epilepsy that may not be as easily amenable to surgical treatment. Approximately 5,000 new surgical candidates are seen in the United States each year. Although most of these are adults, the recent trend toward earlier intervention will undoubtedly increase the number of children and adolescents considered for surgery.
Only the general aspects of surgical treatment are discussed here. The details of presurgical evaluation, operative techniques, and results are available in a host of specialized books and articles (Lüders and Comair, 2001; Wyllie, 2001; Engel et al., 1997; Engel, 1993; Lüders, 1992; Spencer and Spencer, 1991; Wieser and Elger, 1987). The rapidly growing volume of articles and books (Oxbury et al., 2000; Bureau et al., 1998; Wyllie, 2000; Duchowny, 1999; Tuxhorn et al., 1997a; Duchowny et al., 1992) dealing with epilepsy surgery in children testifies to the increasing interest in early intervention (Moshé and Shinnar, 1993).
The aims of surgical treatment are no different from those of any other form of therapy. The ultimate goal is improving the quality of life (QoL) for patients. Control of seizures is the major factor in the QoL (Vickrey et al., 1995), and surgery appears to be a most effective method for achieving complete control. Even when full control has not been achieved, surgery can still greatly improve QoL by significantly reducing the frequency of seizures or limiting the clinical manifestations and practical consequences of uncontrolled attacks (e.g., by suppressing dangerous falls or preventing the generalization of partial seizures). Surgical therapy may also reduce the excessive side effects of drugs, especially those on cognitive or behavioral development. Surgery likely also prevents the aggravation of epilepsy through secondary epileptogenesis or the extension of epileptogenic areas as a consequence of an initially focal paroxysmal activity (Morrell, 1989; Morrell et al., 1989) and thus lessens the noxious effects of epileptic activity, whether clinical or subclinical (Spencer, 1988), although this has not been proven.
IDENTIFICATION OF POTENTIAL SURGICAL CANDIDATES
The first concern is determining whether the seizures are medically intractable (see Chapter 22). This may not be easy because intractability may be difficult to define (Shields, 1997). A full review of the drug history is, therefore, the initial step. This should determine whether the drugs that are most likely to be useful for a particular form of epilepsy have been tested. However, testing all possible drugs is not advisable, because this process would be excessively long when surgery is a reasonable possibility.
Furthermore, increasing evidence indicates that drug therapy is likely to fail to achieve control of the attacks when two of the major drugs have not obtained satisfactory results (Kwan and Brodie, 2000).
Furthermore, increasing evidence indicates that drug therapy is likely to fail to achieve control of the attacks when two of the major drugs have not obtained satisfactory results (Kwan and Brodie, 2000).
The duration of medical trials is a critical point. Although no patient should be operated on without a full, initial attempt at controlling seizures with drugs, the consequences of years of disabling seizures and high doses of antiepileptic medication during a period of neurologic and psychosocial development must be weighed against the risks of surgery. Many investigators now think that intractable epilepsy can be recognized early (Berg et al., 2003; Jallon, 2003; Shinnar and Pellock, 2002; Shinnar et al., 2000); they have indicated that making a decision on surgical therapy should not exceed a duration of 1 or 2 years (Mohamed et al., 2001; Engel and Shewmon, 1992; Kotagal and Lüders, 1992).
The timing of surgery partly depends on the probable effectiveness of the operation available for each particular patient. When a highly efficacious operation is available for the epilepsy of a particular patient, the duration of the medical therapy should be shortened; for instance, in the case of mesial temporal epilepsy without complicating factors, which is controlled by drugs only infrequently, surgery is highly effective. In such cases, surgery without long delays may be preferable to medical therapy, after a short trial has failed to achieve full control of seizures (Engel and Shewmon, 1992). The presence of cognitive and/or behavioral deterioration in association with intense epileptic electroencephalographic (EEG) activity, even in the absence of seizures, is now regarded by many investigators as an indication for early surgery with the hope of preventing further cognitive loss (Arzimanoglou, 2002b; Aicardi, 1997, 1999a; Roulet-Perez et al., 1998; Neville et al., 1997; Shewmon et al., 1997; Deonna, 1996).
Epileptic seizures must be disabling before surgical treatment can be considered. However, what constitutes a disabling seizure disorder is not clearly defined, as this is largely dependent on individual factors, such as lifestyle, psychosocial environment, and personal expectations. Again with the improving risk-benefit ratios of surgery, the growing tendency is to offer surgery for refractory seizures that are less obviously disabling.
CONTRAINDICATIONS TO SURGICAL TREATMENT
Some forms of epilepsy such as the primary generalized epilepsies and the idiopathic focal epilepsies of childhood are absolute contraindications to surgical treatment. As indicated later in this chapter, epilepsies caused by diffuse brain damage are a contraindication to resective surgery, but they may be amenable to palliative surgery in selected patients. Surgery is also contraindicated when the epilepsy is due to an underlying progressive brain disease unless the disease is itself amenable to surgical therapy (e.g., brain tumors).
A severely dysfunctional family or a failure of parents and patients to understand the goals and limitations of surgery is also a contraindication to surgery. Surgery is also contraindicated if it cannot be integrated into a program of rehabilitation.
Another contraindication is the unavailability of a specialized center. Epilepsy surgery mandates a multidisciplinary approach that requires special skills (e.g., neurologists, neuropsychologists, neuroradiologists, neurosurgeons, and nuclear medicine specialists) and sophisticated instruments and materials that cannot be improvised. The indications for surgery depend on a sophisticated global evaluation that can delineate the epileptogenic zone or lesion and can propose a resection that includes the epileptogenic cortex while avoiding unacceptable cognitive or neurologic sequelae. For most cases, the experience of the neurosurgeon in epilepsy surgery might be of considerable importance. In addition, epilepsy centers should offer postoperative rehabilitation programs.
Mental retardation of a severe degree is not an absolute contraindication to surgical treatment if a realistic hope exists that the operation may give sufficient improvement such that the care of the epileptic person is transformed and/or his or her QoL and that of the persons in charge are improved satisfactorily. However, the person and the family must fully understand the limitations of this type of indication in which the objectives are narrowly limited.
Moderate mental retardation is not a contraindication because the occurrence of seizures in a retarded child may considerably increase his or her practical problems and may make the overall management much more difficult (Herman and Austin, 1993; Taylor, 1993). Even if partial control of the seizures is attainable, it may transform desperate situations.
A psychiatric disorder is usually a contraindication to surgery, but it is not a common problem in young children. In adolescent patients, permanent psychosis should discourage the use of surgical treatment, but repeated postictal psychosis is not a contraindication (Taylor, 1993).
TYPES OF AVAILABLE SURGICAL TREATMENT
Several operations are available for the treatment of epilepsy (Table 25.1). The following two major
categories of surgical therapy are used: (a) resective surgery, in which the object is to remove the cortical neuronal pool that is responsible for generation of the seizures, thereby obtaining full seizure control, and (b) palliative or functional surgery, which does not aim at complete seizure control. The latter leaves the epileptogenic area(s) in place but aims to interrupt or limit the propagation of the seizure discharges, thus limiting their clinical manifestations and consequences.
categories of surgical therapy are used: (a) resective surgery, in which the object is to remove the cortical neuronal pool that is responsible for generation of the seizures, thereby obtaining full seizure control, and (b) palliative or functional surgery, which does not aim at complete seizure control. The latter leaves the epileptogenic area(s) in place but aims to interrupt or limit the propagation of the seizure discharges, thus limiting their clinical manifestations and consequences.
TABLE 25.1. Available operations for surgical treatment of patients with epilepsy | |||||||||||||||
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Resective surgery can range from small cortical resections to hemispherectomy. The latter operation has been modified to avoid leaving a large intracranial cavity, which is thought to have been associated with the development of late complications. These consisted mainly of hemosiderosis and hydrocephalus as a result of repeated bleeding in the operative cavity (Rasmussen, 1973). Currently, various methods of functional hemispherectomy (Villemure et al., 1993; Rasmussen and Villemure, 1989) or hemispherotomy (Villemure and Mascott, 1995; Delalande et al., 1992), in which disconnection is more prominent than excision, are preferred.
Palliative surgery (Polkey, 2003) is mostly represented by callosotomy, whether of the anterior half or two-thirds of this structure or complete (Blume, 1997; Gilliam and Wyllie, 1997). Complete callosotomy generally is performed after an anterior callosotomy fails to control seizures rather than as a firstchoice procedure (Spencer, 1988; Spencer et al., 1987a). Subpial transection is another palliative operation (Andrews et al., 1989; Morrell et al., 1989), consisting of multiple subpial cortical incisions that attempt to interrupt the horizontal fibers through which the epileptic discharge is thought to propagate without severing the vertical effector connections, thus avoiding a loss of function of the area where the transection is performed (Morrell et al., 1995, 1997). This technique allows operation on the “eloquent” cortex (e.g., in language or primary motor areas).
Other palliative techniques include vagus nerve stimulation, which requires placement of a stimulator under the skin. In this technique, an electrode is wrapped around the left vagus nerve, so that adjustable pulsed stimuli can be applied (Crumrine, 2000; Ben-Menachem et al., 1999; Schachter and Saper, 1998). The technique is now often used in the treatment of resistant epilepsy that is not otherwise amenable to surgical therapy. Most of the studies that have been published concern adult patients with refractory epilepsy. In children, the results are encouraging with reduced seizure frequency, particularly in the epileptic encephalopathies (Polkey, 2003; Wheless and Maggio, 2002; Majoie et al., 2001; Parker et al., 2001). In addition to requiring an operation and the possible complications that may result from the presence of foreign material, the method is unfortunately costly. Which seizure types or epilepsy syndromes will benefit most from vagus nerve stimulation remains to be defined.
The role of gamma-knife radiosurgery in the treatment of cortical-subcortical cavernous angiomas and hypothalamic hamartomas is undergoing evaluation (Régis, 2001; Régis et al., 2000a, 2000b). Another technique that is still experimental is deep brain stimulation (Benabid et al., 2002; Chabardes et al., 2002; Fisher et al., 1997), the results of which are still too recent to draw conclusions. An extensive review of the palliative techniques, their indications, and results has recently been published (Polkey, 2003).
Some overlap exists between resective and palliative surgery. For example, amygdalohippocampectomy (Wieser and Yasargil, 1987; Yasargil et al., 1985) is most commonly used as a type of resective surgery for the treatment of mesial temporal epilepsy, but it may also be employed as palliative therapy for relieving seizures produced by inoperable brain tumors in posterior parts of the temporal lobe through removal of the mesial structures that amplify and stabilize epileptic discharges of neocortical or extratemporal
origin (Wieser, 1988). The two categories are, therefore, not mutually exclusive. Subpial transection, for example, can be combined with lobectomy or limited cortical resections (Morrell et al., 1989; Polkey, 1989).
origin (Wieser, 1988). The two categories are, therefore, not mutually exclusive. Subpial transection, for example, can be combined with lobectomy or limited cortical resections (Morrell et al., 1989; Polkey, 1989).
Although anterior temporal lobectomy is still the most commonly performed operation (Mohamed et al., 2001; Kotagal and Lüders, 1994; Duchowny et al., 1992; Mizrahi et al., 1990; Engel, 1987), other procedures, such as extratemporal cortical resections (Shewmon et al., 1990; Duchowny et al., 1989), multilobar resections (Shewmon et al., 1990, 1997; Wyllie, 1996; Lüders et al., 1993b), hemispherectomy, and callosotomy are increasingly being performed. This is due to the realization that seizures in children frequently have an extratemporal origin and to the growing awareness of the widely disseminated damage present in many such cases.
It has long been known (Rasmussen 1975a, 1975b) that the best results of resective surgery are in patients in whom a definite lesion is present in the resected brain tissue, not only in tumors but also in atrophic or dysplastic lesions, in which complete control of seizures may be achieved in more than 80% of patients (Munari et al., 2000). The simple removal of an epileptogenic lesion without attempts to define and remove the epileptogenic area (lesionectomy) has been shown to produce control of seizures in a significant proportion of the patients (Munari et al., 2000; Bourgeois et al., 1999b; Cascino et al., 1993; Boon et al., 1991; Hirsch et al., 1989). However, it appears that, in certain cases, the delineation and removal of the epileptogenic area associated with the lesion improves the outcome of lesionectomy (Jooma et al., 1995; Montes et al., 1995; Berger et al., 1993; Cascino et al., 1992b). The current experience confirms that the complete resection of the epileptogenic area is the major condition for a satisfactory surgical result, emphasizing the importance of the presurgical evaluation of the exact location and extent of the epileptogenic zone (Munari et al., 2000, 1985; Cascino et al., 1996; Garcia et al., 1994; Engel, 1993).
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