Pediatric Epilepsy Surgery Medical Author: Harley I. Kornblum, M.D., Ph.D.
Medical Editor: Leslie J. Schoenfield, M.D., Ph.D.
What is Epilepsy?
Epilepsy is the tendency to have seizures. Pediatric epilepsy is the occurrence of these convulsions in children. Seizures can be of several types. The most familiar type is the generalized tonic clonic (Grand Mal) convulsion, in which there is a loss of consciousness and the whole body shakes rhythmically. An absence (Petit Mal) seizure involves a brief loss of awareness, which can be accompanied by blinking or mouth twitching. Petit Mal seizures have a very characteristic appearance on an electroencephalogram (EEG). Partial seizures occur when the convulsion starts in one area of the brain. Simple partial seizures do not cause an alteration of consciousness, whereas complex partial seizures involve some alteration of consciousness. The manifestations, or symptoms, of the seizure depend on where in the brain it starts. For example, a partial seizure originating in the area of the brain that controls hand movements will result in hand twitching. A partial seizure that starts in the area of the brain controlling emotion may result in a fearful feeling. Sometimes, it is difficult to distinguish a partial seizure from a petit mal seizure, but they can be differentiated on an EEG.
What causes epilepsy in children?
Epilepsy can be caused by numerous factors. Many people who have epilepsy begin having seizures in childhood. Epilepsy in children can result from anything that interferes with brain development or function. Some babies suffer a lack of oxygen to the brain before or during birth. This oxygen deprivation can cause cerebral palsy and epilepsy. Some children have bleeding in the brain as a result of prematurity or abnormal blood vessels in the brain (arteriovenous malformations). The bleeding can then result in seizures.
Epilepsy can also be caused by genetic changes. Some children are born with "epilepsy genes" that cause them to have seizures. These seizures may occur early in life or start later--even as late as the third decade of life. Usually, genetically caused seizures are generalized. This means that they do not start in a specific part of the brain, but affect the entire brain all at once. Other causes of childhood epilepsy include brain tumors, infection in the brain (encephalitis), head trauma (injury), and errors in the chemical processes of the body and the brain. In all cases, it must be remembered that the brain of a child is more prone to seizures than is the brain of an adult.
Are seizures bad for children?
Seizures, in and of themselves, can be life-threatening, but this is relatively rare. Children who have prolonged seizures (more than 30 minutes of convulsion) can also have brain damage that is caused by the seizure, but this is also probably rare. However, uncontrolled seizures in children result in severe learning and developmental problems. The goal of treatment in pediatric epilepsy is not only to control seizures, but to improve the developmental potential of the child.
How is epilepsy treated?
The majority of patients who have seizures are relatively easily treated with medication (70 to 80%). Numerous anti-epileptic drugs (AEDs) are now available. The choice of the medication depends on several factors, including the kind of seizures, the age of the child, other medical problems, and the potential side effects of the medicine. Some patients, however, do not respond to the usual medical treatments and are then considered for epilepsy surgery or other treatments.
What is epilepsy surgery?
Epilepsy surgery is a surgical operation to control seizures. There are currently three major categories of epilepsy surgery: - Resective surgery; in which the part of the brain that causes partial-onset seizures is removed.
- Corpus callosotomy; in which the major connection between the two sides of the brain is severed (cut) in order to lessen the severity of some types of seizures.
- Vagus nerve stimulator; in which a small wire electrically shocks the vagus nerve in the neck. This surgery is also performed to limit the severity of seizures.
Each of these three procedures will be discussed below.
Who performs pediatric epilepsy surgery?
Pediatric epilepsy surgery must be performed by a neurosurgeon with specialized training and experience in pediatric epilepsy surgery. Most cases are performed in large academic medical centers with affiliations to medical schools. Prior to the surgery, however, the patient must be evaluated by a competent pediatric epileptologist--usually a neurologist with specialized training in pediatric EEG and epilepsy. The team of epileptologists and neurosurgeons tailor the surgery for each child on an individual basis.
A. Resective Surgery
What is resective epilepsy surgery?
Resective epilepsy surgery is the most proven surgical treatment for partial onset seizures. In this procedure, a portion of the child's cerebral cortex that is causing seizures is removed. The most common resective surgery is a temporal lobectomy, or partial removal of the temporal lobe. The temporal lobe houses structures that are prone to generating seizures. The main functions of the temporal lobe structures are memory and emotion. Usually, the epileptic temporal lobe does not provide these functions, which are then "taken over" by the other temporal lobe. Thus, the removal of the affected temporal lobe does not result in memory or emotional problems. In fact, these functions are often improved after surgery. In young children, there is often malformation of several lobes (parts) of the brain. If these occur in one hemisphere (side) of the brain, then the child may be a candidate for either a multilobar resection (in which a large portion of that side of the brain is removed) or a hemispherectomy (in which the entire cerebral cortex on one side of the brain is removed).
Who is a candidate for resective epilepsy surgery?
The appropriate candidate for epilepsy surgery must meet several criteria. First, it must be determined that the child's seizures are not controllable by medication, or that medical treatment is associated with unacceptable side effects. Second, the seizures must be localizable--that is, they must start from one area or side of the brain. Third, it must be determined that the area in question can be removed without unacceptable problems, such as a loss of language capacity or a severe motor (movement) insufficiency. Children should be considered for epilepsy surgery as soon as they have met the criteria above. There is no benefit in waiting for a child to grow up prior to considering surgery. In fact, there is considerable evidence that the younger a child is at the time of surgery, the better will be their potential for good function after the surgery.
What tests are used to determine if a child is a candidate for resective epilepsy surgery?
First, an MRI is performed to determine if there is an abnormality that requires surgery in any case, such as a brain tumor or certain blood vessel (vascular) abnormalities. The MRI can also identify areas of developmental abnormalities, previous bleeding, stroke , or other problems. An electroencephalogram (EEG) is then performed to determine if the electrical abnormalities of the brain can be identified to occur in one area. If so, or if the results of the initial EEG are in doubt, the child is then hospitalized for prolonged EEG and video monitoring. The purpose of this procedure is to "capture" seizures on video and EEG in order to determine from which part of the brain the seizures are originating. The next steps vary from child to child. In some children, a PET (positron emission tomography) or SPECT (single photon emission computed tomography) is performed when the child is not having a seizure. Often, a seizure-causing brain region (epileptic focus) will appear on these special brain scans even when an MRI is normal. In patients with temporal lobe epilepsy, in which the seizures may be generated from the same part of the brain that is important for language comprehension, a WADA test is performed in order to determine whether removal of that brain area would result in language or memory problems.
Finally, some patients require invasive monitoring, in which an EEG is performed by placing electrodes (monitoring devices) directly within or on top of the brain. This procedure is done to more precisely identify the region of seizure onset. This invasive monitoring may be done at the time of surgery, or may require several days to complete, depending upon the specifics of the case.
There are some other tests that may be useful in evaluating patients for resective epilepsy surgery that will not be discussed in detail. These include an ictal SPECT (a SPECT scan performed during a seizure), magnetoencephalography (MEG) and functional MRI (fMRI).
What are the risks of resective epilepsy surgery?
The risks of epilepsy surgery can be divided into three categories:
- The risk of the anesthesia and surgery: All patients undergoing general anesthesia have a very small risk of death from the anesthesia itself. These risks vary depending on the patient's specific medical problems. The risks of the surgery include severe blood loss as well as the development of hydrocephalous--the obstruction of flow of cerebrospinal fluid, which causes pressure build-up in the brain. Hydrocephalous usually requires surgical treatment. The surgery can also result in infection of the brain, which can be life-threatening. The overall death rate for pediatric epilepsy surgery is probably less than 1% at medical centers that have experience with the procedure.
- The risks of neurological deficits: The goal of resective epilepsy surgery is to maximize the chances for curing the epilepsy while minimizing the potential for creating additional neurological deficits--or abnormal functioning of the brain. Most children who undergo multilobar resection or hemispherectomy already have neurological abnormalities. Epilepsy surgery, however, can worsen existing problems or create new deficits even after careful evaluation. These deficits include problems in movement (particularly hand coordination), sensation, thought, and language. For instance, children undergoing removal of the major motor structures that control hand coordination will never recover the fine movements of the fingers. Remarkably, though, children under the age of nine years who have their major language centers removed will recover language function. In general, the younger the child is at the time of surgery, the better the recovery. The exception is surgery in very young infants (0-5 months), which is considerably more dangerous than at other ages.
- The risk of surgery failure: Pediatric epilepsy surgery usually significantly reduces the number of seizures and improves the lives of the patients and their families. However, complete seizure control, or cure, is achieved in only approximately 50% of the children undergoing surgery. This is probably due to the fact that epilepsy is caused by many developmental problems that can affect many parts of the brain. Epilepsy surgery may remove only the most obvious problem. It is important to note that the seizures of many of those children who have recurrences following surgery are readily controlled with medication.
B. Corpus Callosotomy
What is corpus callosotomy?
Corpus callosotomy is the cutting of the corpus callosum. The corpus callosum is the major way by which the left and the right side of the brain communicate.
Who is a candidate for corpus callosotomy?
Corpus callosotomy is now rarely performed. It is generally reserved for individuals with frequent seizures called "drop attacks". Drop attacks are brief seizures that cause a patient to lose muscle tone and fall to the floor, often causing injury. The corpus callosotomy prevents the rapid spread of seizure activity from one half of the brain to the other, thus preventing a drop.
What are the side effects of corpus callosotomy?
The side effects of corpus callostomy are similar to those listed for resective surgery except that the chance of a severe neurological deficit is much less. However, there is a risk of more subtle problems with the corpus callostomy procedure. Those patients who are relatively unimpaired intellectually prior to surgery may experience odd difficulties in identifying or speaking about certain objects that are placed on one side of the body. This is caused by the lack of communication between the two sides of the brain. There are also other, more subtle abnormalities of thought that the patient may encounter, termed "callosal syndromes".
C. Vagus Nerve Stimulator.
What is the vagus nerve stimulator (VNS)?
The VNS is a device made by the Cyberonics Corporation that is implanted beneath the skin of the chest with wires that lead to the vagus nerve. The vagus nerve goes from the brainstem (the very small lower part of the brain) to many organs in the body. It has been shown that electrical stimulation of the vagus nerve can stop the spread of seizures for reasons that are still unclear to science. After a vagus nerve is implanted it is turned on to be stimulated at a certain strength and frequency. This is called the basal stimulation rate, which can be altered by a practitioner with special training, depending on seizure frequency and severity. Additionally those patients who have auras preceding their seizures--that is, they know when they are going to have a seizure--can use a special magnetic, hand-held device to temporarily increase the stimulator's activity. This may halt the seizure from progressing.
Who is a candidate for VNS implantation?
Patients who have multiple seizure types that are not readily treatable with medication or other forms of surgery may benefit from a VNS implant. Like the corpus callosotomy procedure, VNS implantation may help prevent drop attacks.
What are the side effects of VNS implantation?
Potential side effects of VNS implantation are those from general anesthesia, the failure of the implant to work, and infection at the implant site. Additionally, stimulation of the vagus nerve may cause hoarseness and cough and even changes in the heart rate. Because the VNS is implanted outside the skull, there is little possibility of additional neurological damage.
In summary, pediatric epilepsy surgery can be used to treat a highly selected group of patients whose seizures are not controllable by standard means. Epilepsy surgery must be performed in the setting of a multidisciplinary team consisting of neurologists, neurosurgeons, skilled nurses, and therapists. - Pediatric epilepsy surgery can be used to treat a highly selected group of patients whose seizures are not controllable by standard means.
- The appropriate candidate for epilepsy surgery must meet several criteria.
- There are currently three major categories of epilepsy surgery: resective surgery, corpus callosotomy, and implantation of the vagus nerve stimulator.
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