Epilepsy Surgery
Nearly one of every 100 Americans suffers from epilepsy, defined as recurrent seizures without an obvious cause, such as fever, substance abuse, very high (or very low) blood sugar, or head injury. Seizures are brief episodes of abnormal electrical activity in the brain that alter behavior. Behavioral changes due to seizure activity can take many forms, including waves of fear or depression, hallucinations, "pins & needles" sensations, staring spells, momentary jerks or head nods, and rapid shaking spells (convulsions) lasting minutes or hours.
Having epilepsy increases one's risk of injury or illness due to falls, burns, or choking. People with epilepsy typically are prohibited from driving or operating heavy machinery, limiting their opportunities for employment. Furthermore, the effects of anti-seizure medications and the social stigma of seizures lead many patients with epilepsy to feel that they have no control over their own lives.
Many epilepsy patients achieve good control of their seizures with medicines prescribed by their physicians. Some children with epilepsy stop having seizures while following a strict, very specialized diet. Unfortunately about one in three people with epilepsy continue having seizures in spite of appropriate medical treatment. Recent advances in medical technology and surgical techniques mean that most of these patients with drug resistant (pharmacoresistant) epilepsy can be helped with some type of surgery.
Pre-surgical Evaluation
Electroencephalography (EEG) - This is the first and most important tool for evaluating epilepsy. EEG detects the brain's natural electrical activity and helps specially trained physicians (neurologists) diagnose and classify epilepsy. When combined with video monitoring in a special hospital unit devoted to epilepsy evaluation, EEG can help neurologists determine what part of the patient's brain is responsible for their seizures.
Neuroimaging - Many imaging techniques have been introduced and developed over the past two decades that provide very detailed information about the brain as it relates to epilepsy. These tests, performed and interpreted by specialists in radiology and nuclear medicine, reveal information about the structure and activity of a patient's brain.
Anatomic: Current magnetic resonance imaging (MRI) scanners produce very detailed, high-resolution pictures of the brain. These images can reveal tumors, blood vessel abnormalities, or congenital malformations that may be responsible for a patient's seizures.
Functional: positron emission tomography (PET) scanners are used to detect areas of the brain that are abnormally under- or overactive compared to the rest of that individual's brain. Single photon emission computed tomography (SPECT) scans performed immediately after a seizure can outline the brain region where that seizure began.
Neuropsychological Testing - Neuropsychologists are doctors of psychology who study the relationship between human behavior and brain function. Detailed written and oral testing by a neuropsychologist can help determine how well various regions of an epilepsy patient's brain are working. The testing usually focuses on language and memory abilities. Sometimes this information can help to localize the origin of someone's seizures. More often, however, it provides an estimate of how well an epilepsy patient will be able to function after epilepsy surgery.
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Diagnostic Procedures
The results of the tests mentioned above are frequently enough to recommend an operation. If not, however, the following invasive tests can provide additional information for surgical planning.
Wada Test - Memory and language abilities can be compromised if those areas of the brain are treated surgically. This test helps to locate those areas within an individual patient's brain so they can be preserved during surgery. It requires catheterization of the blood vessels that supply the brain and is typically an outpatient procedure.
Intracranial Monitoring - When all the other tests fail to indicate the exact source of a patient's seizures but still point to one area of the brain, a staged surgery may be recommended. In this case, the patient will have an operation to place temporary EEG monitors inside the skull, directly on the brain. The patient is then monitored in the hospital so their seizures can be recorded and analyzed by the Neurologist. Brain mapping is performed as well to outline areas responsible for critical functions, such as language and control of movement. A second operation is then performed, guided by the seizure recording data and the brain map, to eliminate the seizures and remove the EEG monitors.
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Curative Procedures
These operations are performed by specially trained neurosurgeons in close cooperation with neurologists to eliminate seizures and cure the patient's epilepsy.
Temporal Lobectomy - The most common type of epilepsy treated with surgery is so-called "temporal lobe epilepsy." This form of epilepsy typically affects teenagers or young adults and usually cannot be controlled with medicine. The seizures arise from an abnormal or damaged region of the temporal lobe that can often be seen on MRI. Surgical removal of key portions of the abnormal temporal lobe will eliminate seizures for at least 80% of these patients.
Extra-temporal Cortical Resection - Seizures that originate outside the temporal lobe take many forms and have many possible causes. When these seizures are associated with a clear abnormality (such as a tumor or brain malformation), surgical treatment offers a 70-80% chance of stopping them. When no clear abnormality is detected, and intracranial monitoring is required, the patient's chance of becoming seizure free drops to 50-60%.
Hemispherectomy - Certain severe forms of epilepsy in children involve most or all of one side of the child's brain (hemisphere). If the other hemisphere is normal, the child's potential for development can be made much better by eliminating the bad side. The current technique involves disconnecting the diseased hemisphere from the rest of the brain and has a success rate of 50-60%.
Palliative Procedures
These operations are performed to help control seizures in patients with incurable epilepsy.
Vagus Nerve Stimulation - Vagus nerve stimulators are a useful tool in the management of difficult-to-treat seizure disorders. This relatively simple surgical procedure typically provides a decrease in seizure frequency and/or severity but does not eliminate all seizures. Patients frequently report an improvement in their quality of life and often can reduce their seizure medicines as well. Candidates for the vagus nerve stimulator are generally people who have frequent seizures that adversely affect the quality of their life. These patients usually have had epilepsy for many years, have failed multiple anti-seizure medications, and are not candidates for any other surgical treatment.
Surgical implantation of the stimulator involves attaching electrodes to the left vagus nerve (located in the neck) that are connected to a generator placed in a pocket under the skin made just below the left collar bone. The procedure itself takes about an hour and is usually done in the outpatient setting.
The patient can begin using the stimulator under the guidance of a neurologist usually within one week of surgery. Once activated the device works much like a pacemaker, sending impulses to the brain on a schedule programmed by the patient's neurologist. The patient is also provided with a hand-held magnet that can activate the vagus nerve stimulator when he or she senses a seizure coming on.
This is a simple procedure with a good response rate and a low frequency of complications.
Corpus Callosotomy - Some patients suffer frequent falls (and numerous injuries) due to an uncommon seizure called a "drop attack." These seizures cause sudden loss of muscle control throughout the patient's body and come on without warning. While this seizure type cannot be cured surgically, the falls can be eliminated by partially disconnecting the hemispheres from one another. This prevents the seizures from crossing over from one side of the brain to the other hemisphere.
On average, seizure frequency decreases by about 75% after corpus callosotomy. Potential side effects of this procedure include adverse effects on language function and behavior. This procedure fell out of favor after vagus nerve stimulation was introduced but it is still available for carefully selected epilepsy patients.
For more information, please visit the University of Buffalo Comprehensive Epilepsy Program - www.buffaloepilepsy.com.
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