|Year : 2007 | Volume
| Issue : 5 | Page : 28-32
Epilepsy surgery in childhood
Judith Helen Cross
Neurosciences Unit, UCL-Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust, London, United Kingdom
Judith Helen Cross
Neurosciences Unit UCL-Institute of Child Health, The Wolfson Center Mecklenburgh Square London, WC1N 2AP
| Abstract|| |
Surgery is now an established treatment for drug resistant symptomatic focal epilepsy in childhood. The aim is to resect the focus of epileptic seizures without functional compromise. A wide range of procedures may be considered from focal to multilobar resections and hemidisconnection procedures, the most common pathology being malformations of cortical development. Seizure freedom will be seen in 40-80% dependent on the underlying pathology and completeness of resection/disconnection of the epileptogenic zone. When likely long-term benefits are evaluated, surgery should be considered early in these children.
Keywords: Epilepsy surgery, children, MRI, SPECT
|How to cite this article:|
Cross JH. Epilepsy surgery in childhood. Ann Indian Acad Neurol 2007;10:28-32
Surgery for focal epilepsy in childhood is not new; however advances in neuroimaging, neuroanesthesic and neurosurgical techniques have reduced morbidity and have made it a more realistic consideration, particularly in the very young. The key is who should be considered and at what point in the natural history of the epilepsy. It is now established that early onset epilepsy is associated with a high rate of long-term morbidity; children are at a higher risk of continued seizures (with associated morbidity and mortality) and of developmental, behavioral and psychosocial compromise. There is also established evidence that resective surgery in appropriate circumstances has a high chance of relieving of seizures and of consequently reducing such comorbidities.
One question that may arise is whether there is an optimal age for surgery; should it be performed as early as possible or should we wait for a number of medications to be tried first. With regard to proving drug resistance, adult criteria suggest a requirement of trial of at least two drugs over at least two years. Whilst appropriate in the older child, an infant may trial twice as many drugs over as many months. Therefore surgery should be considered in a child with focal epilepsy when there is inadequate control of seizures despite an appropriate trial of anticonvulsant medication. Age at surgery probably has little influence on seizure outcome. Limited series of surgery performed in the very young (<3 years) suggest that initial 12m outcome with regard to seizure freedom is similar to the older child and again is more likely to be related to the underlying pathology and procedure performed. It may be presumed however that if children are recognized early and seizures stopped through surgery, this has the potential to minimize psychosocial morbidity long-term.
| Procedures in Children|| |
Two different types of procedure may be considered in epilepsy surgery practice; resective procedures are aimed predominantly at removing the epileptic focus, with minimal if any interference in function. Functional procedures (corpus callosotmy, multiple subpial transection) do not involve removal of brain tissue, but aim to reduce seizures with alteration of brain function. Several resective series from major centers are now published and report similar proportions of temporal and extratemporal resections as well as hemispherectomies.,, Whereas in adult epilepsy surgery practice temporal lobe resection remains the most common procedure for mesial temporal sclerosis, a recent ILAE survey confirmed that in pediatric practice two thirds of procedures performed are multilobar resections and hemispherectomies, predominantly for malformations of cortical development [Figure - 1].
Functional procedures are performed to a limited degree in selected centers. Corpus callosotomy is directed at alleviation of drop attacks, whatever the semiology. Multiple subpial transection was initially proposed to minimize epileptic spread by division of transverse fibers, with preservation of function by leaving longitudinal tracts intact. It may be considered with or without lesionectomy, where the seizure focus lies in functional cortex, such as motor cortex, or Wernickes in Landau Kleffner syndrome (acquired epileptic aphasia) where the driving focus has been lateralised preoperatively.
| Presurgical Evaluation|| |
The aim of presurgical evaluation is to assess the individual child as to whether seizures arise from a single functionally silent area of the brain - that is to determine whether an area can be removed successfully, curing seizures with minimal, if any, functional consequence. In the majority selection is easier in the presence of a lesion that is concordant with seizure onset [Figure - 2]. In children who undergo focal resection the aim will be no functional deficit. In children who undergo hemispherectomy or other hemidisconnection procedure it is likely they will have a pre-existent congenital hemiplegia with structural brain abnormality of the contralateral cerebral hemisphere. Such children will suffer a homonymous hemianopia if not already present and not regain any fine finger or toe movement. Language dominance should be determined preoperatively; in children with early onset epilepsy and congenital hemiplegia it is likely to be within normal cortex, but in progressive conditions such as Rasmussens, this will need to be given careful consideration if the dominant hemisphere is affected.
Advances in neurophysiological and neuroimaging techniques have enabled a predominantly non-invasive evaluation in the majority. Which techniques may be used in the decision-making process will on the whole depend on the experience of the center. The ILAE subcommission for pediatric surgery recently agreed that interictal and ictal EEG recording (with video), MRI with a specified epilepsy protocol, with specific sequences for children under the age of two years and age appropriate neuropsychological/developmental assessments are mandatory; in addition all pediatric epilepsy specialist units should have access to functional imaging capabilities (ictal and interictal SPECT, PET) and neuropsychiatric evaluation is recommended. Functional MR studies may aid define motor and language cortex in relation to lesions in older selected cases., Some consideration has been given to the presumption that in children with early onset temporal lobe epilepsy reorganisation of memory is likely to have taken place. However, presumptions cannot be made and language has been found to be localized within malformed cortex even in the presence of early onset epilepsy in contrast to epilepsy associated with early postnatal insults. Invasive electrode studies are indicated primarily to localize the epileptogenic region when alternative methods are inconclusive or where the focus may lie in close proximity to what is believed to be functional cortex. The complexity of investigation and vulnerability of certain groups of children, particularly infants and toddlers, as well as older candidates for hemispherectomy and multilobar resection, mean evaluation should be undertaken at a specialist surgical unit with experienced, multidisciplinary personnel and access to advanced technologies.
| Specific Situations|| |
It has become clear that despite this being a condition with multifocal brain abnormalities, where seizures are demonstrated to be arising from a likely single tuber, resection of that tuber may lead to significant reduction in seizures if not seizure freedom., Some data has suggested that in a selected few, multiple procedures may lead to benefit. However, it is difficult to counsel the likelihood of long-term seizure freedom with little long-term outcome data. Jarrar et al reviewed 21 patients 1-14 years following surgery; at 12 m 59% (13/22) were seizure free as opposed to 42% (9/21) at five years. The possible developmental benefits as a result of this are self-apparent although unproven.
This condition is characterized by the association of a facial capillary angioma involving the periorbital area, the forehead and the scalp, with an underlying leptomeningeal angioma, unilateral in the majority. Eighty percent of children develop epilepsy, the majority doing so under the age of two years, Such children are at high risk of developing a progressive hemiplegia and cognitive plateau or regression in association with clusters of focal seizures. In children with early onset epilepsy resistant to medication early surgery with resection of the affected area is advocated, with retrospective series suggesting better cognitive outcome in those operated at an earlier age.
Rasmussen encephalitis (RE) is one condition that requires careful diagnosis, review and follow-up in a surgical center specializing in the condition. This is a progressive condition; children typically present with focal epilepsy that becomes resistant to medication. Associated with this there may be progressive hemiparesis with or without cognitive decline, with progressive unilateral cerebral atrophy seen on MRI; clinically certain diagnostic criteria have been outlined [Table - 1]. On pathology changes are seen consistent with chronic encephalitis; however the etiology remains unknown. It is presumed to be an autoimmune process, possibly T-cell mediated. Although medical therapies have been trialed (e.g., immunoglobulin, steroids, immunosuppression) the only definitive curative treatment of seizures is surgery, as a hemidisconnection procedure (e.g., hemispherectomy, hemispherotomy) with the inevitable functional consequences of permanent hemiplegia and hemianopia. The decision as to when this should be inflicted will be influenced by the degree of clinical progression of the disease. In dominant hemisphere Rasmussens encephalitis the likely timing of surgery will be influenced by the likelihood of language recovery, compared to the severity of the disease and degree of cognitive decline. Although original data suggested early onset of disease optimized outcome, cases have now been reported of later surgery with subsequent limited recovery of language. The decision to perform surgery is often challenging, as the risk-benefit assessment require considerable clinical experience and review of the individual patient.
The syndrome of drug resistant epilepsy, with gelastic seizures almost synonymous with associated behavioral and cognitive comorbidity is now well recognized in association with hypothalamic hamartoma. Recent data suggest ablation (through gamma knife therapy) or removal/disconnection, of the hamartoma gives greatest chance of seizure freedom, with improvement in the behavioral profile. However, evaluation and procedure considered requires a highly skilled, multidisciplinary team with experience in the condition.
| Outcome|| |
The primary aim of epilepsy surgery is seizure freedom, with no unpredictable functional deterioration. Secondary aims may be of equal if not of primary importance to some families and require careful consideration and consequent counseling prior to surgery. Seizure freedom may be achieved in 40-85% children dependent on complete or incomplete resection of structurally or electrically abnormal tissue, underlying pathology as well as the type of procedure performed, with a wider range of procedures performed and greater proportion with developmental malformations in children when compared to adults.,,
In children undergoing wider resections such as hemidisconnection procedures, seizure outcome appears primarily to be related to underlying pathology, with lower rates of seizure freedom for developmental malformations, particularly hemimegalancephaly, although the completeness of disconnection will be relevant. The type of procedure performed, whether anatomical or functional hemispherectomy, hemispherotomy or hemidecortication will depend on the neurosurgeon, who in turn may decide on a particular procedure on considering pathology and structure. Data to date give little comparative outcome figures for different procedures in the hands of a single neurosurgeon.
A further factor that needs to be considered with regard to seizure outcome following surgery is at which point in time the outcome is measured. Two series to date review outcome at up to 10 years following surgery and again find that pathology may determine whether seizure freedom is seen long-term, with developmental malformations showing a reduced seizure outcome long-term. This is also of importance when considering children with multifocal disease such as tuberous sclerosis., Very little work has been done on anticonvulsant reduction following surgery in children, often a further aim of parents. Different centers have varying practices with regard to perioperative and postoperative drug reduction. Data suggest however that although there are predictive factors with regard to seizure freedom, reduction or withdrawal of anticonvulsants cannot be guaranteed.,
Following hemidisconnection procedures certain functional deficit may be inevitable such as visual field defects in those where they do not preexist (homonymous hemianopia) or increased motor dysfunction where preoperatively fine finger movement is preserved. In the majority preexistent structural disease and contralateral hemiplegia indicate it as unlikely that deterioration in function will be seen. With regard to language dominance, again preexistent structural abnormality and early onset epilepsy imply contralateral hemisphere dominance. However special consideration needs to be given to Rasmussens Enephalitis as discussed above.
The rate of cognitive dysfunction in those coming to surgery is high particularly related to early age of onset of epilepsy. Although developmental improvement is often desired following surgery, there are few prospective studies reviewing overt evidence for this. A recent study reviewed developmental outcome in children at least 6-12 m following resective surgery and showed a significant number continued to perform at their preoperative levels; this may be significant as IQ is a measure of performance relative to normal peers implying a maintained trajectory. It is presumed such gains would not be made in a similar group with continued seizures.
Early data from children undergoing temporal lobectomy suggested little overall risk to cognitive function with recent data suggesting greater likelihood of improvement in children than adults 12 months following surgery when compared to preoperatively. Similar is seen following hemidisconnection procedures, most studies report little longitudinal change in IQ.,, Pulsifer et al . reported poorer developmental outcome following surgery where the underlying pathology was developmental, as opposed to Rasmussens Encephalitis, stroke or vascular pathology, although numbers in the latter two groups were very small. They also determined however that children with developmental pathology had a significantly lower IQ presurgery, with no significant gain post surgery. It was also evident that the group of children undergoing surgery for developmental malformations however had a significantly lower age of onset of epilepsy (<12 m) than the other groups, which is likely as suggested from other studies to have a greater bearing on outcome. Comparative studies are required over a much longer duration of follow-up to determine the relative merits of surgery on developmental outcome, although even limited studies available suggest seizure outcome and age at surgery are likely to influence this.,
Behavior can often be seen to be the most problematic issue in children with ongoing epilepsy and developmental delay, but the impact of surgery is more difficult to assess and therefore predict. Hemispherectomy was originally advocated for infantile hemiplegia, epilepsy and behavior disorder. In one series of children undergoing the procedure for a variety of pathologies, Devlin et al. found 10 reported by parents to have preoperative behavior difficulty. Fifteen however reported postoperative improvement. However in another large series of 53/71 children who underwent hemispherectomy for dysplasia, Rasmussen or vascular etiology where the Child Behavior Checklist, was evaluated no differences were determined in scores pre or postoperatively. The rate of psychiatric diagnosis in children coming to temporal lobe surgery is high; as high as 72% in one series. In 16% mental health problems resolved postoperatively, but in 12% they evolved. There was no clear relationship between seizure freedom postoperatively and any psychiatric disorder or with AED usage, type of surgery or cognitive ability for the group as a whole.
| Summary|| |
Surgery for epilepsy in children can confer considerable benefits to the individual and the family. Children with symptomatic focal epilepsy should therefore be considered early in their natural history. Evaluation and subsequent surgery however should be undertaken in specialist centers with experience in the technologies involved.
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[Figure - 1], [Figure - 2]
[Table - 1]