New Way to Map Brain Helps Surgeons Cure Some Epilepsy
By SANDRA BLAKESLEE
Published: October 25, 1988
USING advanced electric probes and radio transmitters developed for the space program, physicians are mapping the brains of people with certain types of epilepsy. By pinpointing the damaged areas of the brain more precisely than has been previously possible, doctors are able to perform surgery that seems to cure the disorder in most of these patients.
Doctors stress that the technique, available at only a handful of American medical centers for about five years, works only on epilepsy patients whose seizures can be localized to a single area of the brain and who do not respond to drugs.
Of the two million Americans with epilepsy, at least 100,000 fit these criteria and could benefit from surgery, said Dr. Robert J. Gumnit, director of the Minnesota Comprehensive Epilepsy Program. Unfortunately, he said, no more than 500 to 1,000 are getting the surgery each year because few primary physicians and neurologists are recommending it. 'Improved Efficacy and Safety'
''The realization that epilepsy surgery has undergone an explosion in the last five years, with greatly improved efficacy and safety, has not caught up with patients and physicians,'' said Dr. Jerome Engel, a leader in epilepsy surgery at the University of California in Los Angeles.
Physicians may be concerned about the risks of surgery, but there are also risks to continuing seizures, said Dr. James J. Cereghino, chief of the epilepsy branch at the National Institute of Neurological, Communicative Disorders and Stroke in Bethesda, Md. The only major criticism of the surgery, he said, is that the long-term prognosis is not yet known.
A preoperative evaluation, in which the brain is mapped at an epilepsy center, can cost $20,000 to $90,000, Dr. Engel said. But he said the costs are justified. ''Before you take out a piece of someone's brain, especially a compromised brain, you should be sure you know what you're doing ahead of time,'' Dr. Engel said.
Epilepsy is not a disease, Dr. Gumnit said. It is a symptom of an underlying problem such as a tumor, a head injury, high fever in infancy or one of 500 other causes. Although there are some inherited forms, he said, most people are not born with it.
Epilepsy is marked by disturbed electrical rhythms in the brain and typically triggers occasional convulsions and clouding of consciousness. It may not develop until several years after the brain has been damaged. Because of the seizures, patients with epilepsy often must limit their activities. In most states, for example, people with uncontrolled epilepsy are unable to get a driver's license. Best Candidates Are Young
The physicians stressed that young people, from early adolescence to early adulthood, are the best candidates for surgery. The goal is to intervene early so that an adolescent can avoid becoming dependent on others and can enjoy a more typical life. But because seizures sometimes disappear in children over the age of 12, many physicians prefer to wait until adolescence to intervene.
There are two major kinds of seizures, generalized and partial. Generalized seizures are sudden and affect the entire brain, Dr. Gumnit said. Victims often lose consciousness. Fortunately, drugs help 80 percent of these people, he said. With few exceptions, they are not surgical candidates.
Partial complex seizures, experienced by 40 percent of epilepsy patients, come on more slowly and tend to begin on one side of the brain before spreading, Dr. Gumnit said. Victims may stop what they are doing, stare, chew, make odd hand gestures and seem out of touch with their surroundings. An attack can last a minute or more, followed by confusion and memory loss. Only a third of these patients respond to drugs.
Partial complex epilepsy with an identifiable focus on one side of the brain is the most amenable to surgery, Dr. Engel said. The trick is to identify the damaged section of the brain, and remove it without harming the good portion. The damaged tissue looks normal on diagnostic tests such as CT scans and magnetic resonance imaging, but can be pinpointed with certain electrical monitoring. Mapping Techniques Are New
Epilepsy surgery is not new. It has been tried, with mixed results, for 100 years. What is new are techniques that allow doctors to draw a functional brain map before surgery.
Dr. Gumnit recommended that a person whose epilepsy has not been controlled after a year to a year and a half on drugs be referred to an epilepsy center for evaluation.
In phase one of the evaluation, Dr. Engel said, patients move in to a hospital, where their brain waves are monitored for one to two weeks and every move is videotaped.
Patients wear 21 scalp electrodes, glued to the head, along with two needle-like electrodes in the jaw muscle to pick up signals from within the brain. The electrodes are attached to a radio transmitter, originally developed for the space program, that is held on the head by bandages. Brain waves are transmitted to a recorder in another room.
About a third of the patients will have a lesion, or clump of damaged tissue, in the left or right temporal lobe, Dr. Engel said. This is an area deep in the brain where, among other things, memories are processed.
If the brain-wave patterns point to a single temporal lobe as the source of trouble, doctors will run more tests to confirm the diagnosis and then will consider removing the lobe. At least 75 percent of patients who have a temporal lobe removed have no more seizures, with little loss of function, Dr. Gumbit said. Most others experience far fewer seizures.
But external electrodes are not useful in all cases, the physicians said. In many patients, monitoring indicates a more complex problem, with seizures emanating from both sides, or from higher up in the brain. In phase two evaluations, brain waves are again monitored for several weeks, but the procedure is more invasive. Depth Electrodes Employed
If physicians still believe that one temporal lobe is bad, or that both are damaged but one is worse, they use depth electrodes. Under general anesthesia, tiny holes are drilled into the skull just above the ear and long needles with electrodes are inserted.
''We may see seizures that start in deep, specific areas that we did not pick up with surface electrodes,'' Dr. Engel said. In that case, he said, the more damaged temporal lobe is removed. The other lobe, although sick, may be able to function normally or at least produce fewer seizures.
But if the seizures seem to start higher up in the frontal lobe, parts of which control speech or movement, physicians try a second strategy to get a better brain map. Under anesthesia, a chunk of skull is removed and a plate of 64 or more electrodes is placed onto the brain.
Dr. Gumnit said physicians can pinpoint functional areas by turning on one electrode at a time. He said it is possible to draw a map so that surgeons know where they are going with hairbreadth accuracy.
Of these patients treated in Minnesota, he said, 63 percent are free of seizures after surgery, while 22 percent have a reduction of 90 percent or more in their seizures. The few remaining patients could not be helped because their lesions were too close to vital areas of the brain.
The risk of these procedures includes postoperative bleeding, infection and sometimes depression, the physicians said. A few people experience temporary weakness on one side or a small loss in their visual field.