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Epilepsy, or recurrent, unprovoked seizures, affects 0.5-1% of the population, with the most frequent incidence being in childhood. Every year approximately 25,000-40,000 children in the United States experience their first seizure that is not associated with a febrile illness or head trauma. 30-65% of these children go on to have a second unprovoked seizure within the first year. Fortunately, in most patients, the seizures can be controlled adequately with medication, and in some cases, the epilepsy will resolve over time. However, roughly 30% of children with epilepsy cannot be controlled with medication. In addition, even in children with well-controlled epilepsy, the side effects associated with long-term medication use can be significant. Epilepsy surgery offers an alternative means of treating seizures.
Video: Epilepsy surgery
Dr. Lew, medical director, neurosurgery explains what types of epilepsy surgeries are available.
Early intervention is key
Infants and children have specific vulnerabilities to even brief, recurrent seizures. Young, immature brains can essentially learn to seize more easily over time through the establishment of new connections in the brain. This results in progressively more difficult to control seizures. The consequences of continued seizures on the immature, developing brain are severe; developmental delays, behavioral difficulties, and irreversible cognitive declines are the norm. If the seizures can be stopped, whether with medication or epilepsy surgery, windows of “developmental opportunity” can open. The result is significant developmental gains, gains that would not have been seen if the uncontrolled seizures had persisted.
Fortunately, it does not take years to determine if a patient’s epilepsy will be controllable with medication. 60% of children will be controlled with the initial medication prescribed. Of the 40% whose seizures persist, only an additional 10% will achieve good control with a second appropriately chosen drug. For the remaining 30%, adequate control is unlikely to be achieved with subsequent medication trials.
Even in children whose epilepsy is well controlled, the consequences of epilepsy, and the side effects from medication, can be considerable. Because of this, epilepsy surgery should be considered in patients who cannot be adequately managed with medication alone.
Surgery is not a last resort
There is a tendency to view brain surgery as a high-risk endeavor that should be reserved for the most difficult cases. While there are certainly risks associated with epilepsy surgery, they are often far-outweighed by the risks of continued poor seizure control, as well as the quality-of-life benefits associated with seizure freedom or improved seizure control. Advances in diagnostic and surgical techniques have improved success rates and decreased complication rates.
Unfortunately, patients are often unsuccessfully managed for several years before being referred for surgical evaluation. Over that time, the patient often suffers irreversible cognitive losses, while the epilepsy becomes more difficult to manage/cure. The developing brain of a child is much more plastic than that of an adult, which makes it possible for eloquent functions such as motor control and language to re-establish in other areas of the brain in a young child - a feat not possible in a mature brain. Thus, it is important that surgical options be considered earlier in the course of treatment, rather than as a "last resort."
Determinants of surgical candidacy
The decision of whether or not a child is a candidate for surgery is made by a multidisciplinary team. Evaluations require expertise from a variety of fields, including neurology, neurosurgery, neuropsychology, and radiology.
Diagnostic tests used to assist with decision-making include:
- Video electroencephalographic (EEG) monitoring
- Magnetic resonance imaging (MRI)
- Other neuroimaging
- Functional MRI (fMRI)
- Magnetoencephalography (MEG)
- Positron emission tomography (PET)
- Single photon emission computed tomography (SPECT)
- Neuropsychological testing
Questions that are considered when determining surgical candidacy:
- Is there a specific lesion that appears to be generating the seizures?
Seizures associated with structural lesions seen on MRI, such as tumors, focal cortical dysplasias, vascular malformations, hamartomas, infarcts, and mesial temporal sclerosis, have a higher success rate with surgery.
- What is the prognosis for continued non-surgical therapy?
If a patient has failed more than two medications, it is likely he/she will continue to have seizures. Some epilepsy syndromes, such as benign rolandic epilepsy, improve over time. Other syndromes have a predictable, progressive course leading to uncontrolled seizures that can only be cured with surgery. Knowing the cause of the epilepsy can help with decision of whether to consider surgery.
- Is it likely that a region of the brain causing seizures can be identified and safely treated?
Much of the pre-operative assessment is geared towards determining the likelihood that a focal area exists that can be removed or disconnected without causing harm to the patient. If the area causing seizures is suspected but not certain, the patient may require surgery to implant electrodes in the skull to better define the source of the seizures and to define areas of the brain where important motor or language functions reside. If seizures are coming from multiple areas of the brain or important areas of the brain for function, surgery may not be an option.
- Is there a role for palliative surgery?
Some children cannot be made seizure-free with surgery but can still benefit from a reduction in the frequency and/or severity of seizures.
A variety of surgical techniques is used to treat pediatric epilepsy. The appropriate surgery is determined by the extensive pre-surgical evaluation. In many cases the initial surgery is diagnostic (information gathering) – electrodes are temporarily implanted on the surface or inside the brain to get better information regarding where the seizures are coming from and where the critical areas of the brain are for motor and language function. There are five broad categories of therapeutic surgical techniques:
- Resection. Surgical resection (removal) of an area of the brain causing seizures is the mainstay of epilepsy surgery. Resections can be small or large. At the extreme end of the spectrum, the entire cerebral hemisphere can be removed or disconnected (hemispherectomy).
- Disconnection. If an area causing seizures is disconnected from the rest of the brain, the seizures can be cured (if the only connection is cut), or made significantly more manageable by slowing conduction (by eliminating the main pathway of spread). Disconnections are often performed to minimize the risks associated with resections that are more extensive. An example of disconnection surgery is sectioning of the corpus callosum (corpus callosotomy). The corpus callosum is the main highway of communication between the two halves of the brain. Disconnecting the corpus callosum will slow the spread of seizures, thereby reducing the severity of seizures and often eliminating drop attacks (sudden loss of consciousness causing falls).
- Stimulation. There is a trend in epilepsy towards non-destructive techniques involving electrical stimulation of the nervous system. Currently, vagus nerve stimulation (VNS) is the only mainstream stimulation technique used in children. It is typically reduces seizure frequency and severity but does not result in complete freedom from seizures. Deep brain stimulation (DBS) and cortical stimulation are techniques that show promise in adult human trials for managing some forms of epilepsy but have not yet been made available to children.
- Stereotactic laser ablation. Ablation refers to the destruction of seizure causing brain (or tumor) without removal. For epilepsy, this can be done in a minimally invasive manner via stereotactic laser ablation (SLA). Under anesthesia, through a small hole in the skull, a small laser fiber is placed into the area of interest. The laser is then activated to destroy the area from within under MRI guidance. The advantages of this new technique include shorter hospital stay (typically one night), less discomfort, and less risk. Unfortunately, not every patient is a candidate for this procedure. Children's Hospital of Wisconsin is one of the few hospitals in the country that is using this technology, and currently the only hospital in Wisconsin.
- Multiple Hippocampal Transections (MHT). MHT is a relatively new procedure, originated in Japan, to treat epilepsy coming from the hippocampus – a deep area of the brain that is involved in memory functions but also is often a source of seizures. Traditionally when seizures are coming from the hippocampus, the hippocampus may be surgically removed or destroyed to eliminate seizures. Unfortunately for some patients this may result in decreased memory function. MHT is a technique where the hippocampus is modified to eliminate seizures while preserving memory function. Our epilepsy surgeons have traveled to Japan to learn the technique in order to offer this option to children who may benefit from this innovative procedure.
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