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EPILEPSY SURGERY

WHO IS IT FOR? DOES IT WORK?

 



Selim R. Benbadis, MD
Associate Professor (Neurology & Neurosurgery)
Director, Comprehensive Epilepsy Program
University of South Florida College of Medicine
Tampa, FL
(813)259-0605
http://www.med.usf.edu/~sbenbadi

 

INTRODUCTION

Overall, drug therapy is effective for about 70% of patients with epilepsy. However, if medications are not effective after a certain period of time, surgery is an appropriate and well-accepted treatment for some types of epilepsy. Unfortunately, many treating neurologists who do not specialize in epilepsy fail to inform their patients that surgery is an option for severe epilepsy, and many patients who could benefit from surgery are unaware of that possibility. Of the 30% of patients whose seizures cannot be controlled with drugs, approximately half (more than 100,000 in the United States) may be candidates for epilepsy surgery. Yet only about 3,000 epilepsy surgeries are performed annually in the U.S, indicating a great need for more information about surgery of epilepsy.

 

THE EVALUATION FOR EPILEPSY SURGERY

Surgery is only considered the appropriate treatment when medications fail to control the seizures. When several medications regimen have been unsuccessful, surgery should at least been considered and discussed. When surgery is contemplated, a comprehensive evaluation is performed to ensure that the operation is likely to improve the seizures and will not cause damage to essential functions such as speech and memory. The evaluation requires prolonged EEG-video monitoring and other tests to pinpoint the exact location of the injured brain cells causing the seizures. The location of the damaged cells determines whether the surgery can be performed and what technique is used. Much like other complex operations such as transplants, the evaluation for epilepsy surgery is multidisciplinary. It is directed by a neurologist specializing in epilepsy (an epileptologist), with the input from other specialists including neuroradiologist, neuropsychologist, social worker, and of course the neurosurgeon.

 

  1. Phase I evaluation

 

  • Prolonged EEG-video monitoring

This is the first and essential phase for all potential candidates to a surgical treatment, and in general for patients whose seizures are uncontrolled. With electrodes attached to the scalp, EEG equipment and video cameras are used to record seizures and monitor the

brain's activity. It is usually done continuously 24 hours a day, and may last from a few hours to several weeks, depending on the time needed to record a sufficient number of seizures. It is often necessary to reduce or discontinue antiepileptic drugs, in order to obtain seizures within a reasonable time. EEG-video monitoring first confirms the diagnosis of epilepsy, since it is the only way to make a positively certain diagnosis of epileptic seizures. It is not uncommon, during this phase, to find that the "seizures" are actually non epileptic in origin, but rather psychogenic. This occurs in 10 to 20% of patients referred to an epilepsy center for intractable epilepsy. EEG-video monitoring clearly allows to clearly distinguish between partial (focal) epilepsy, where seizures are triggered by a localized area, and generalized epilepsies, where seizures arise from the whole brain. If seizures are focal, it usually allows localization of the zone of seizure onset.

  • Imaging

An MRI of the brain is always necessary, and may show a variety of localized abnormalities. However, it is very often normal, and this does do preclude surgical treatment. Other imaging techniques complement the MRI, and include positron emission tomography (PET) and single photon emission tomography (SPECT).

  • Wada testing (intracarotid amobarbital test)

This procedure is used to delineate areas of the brain that control language and memory function. It is performed during an angiogram (dye injected into the arteries). One hemisphere at a time is anesthetized for several minutes. Language and memory are then tested. The procedure is then repeated for the opposite hemisphere.

  • Neuropsychological testing

An extensive battery of tests are performed to help in localizing abnormalities to specific brain regions, and to predict (and prevent) possible consequences of surgery.

 

  1. Phase 2 evaluation

In some cases, the phase I evaluation fails to pinpoint the location of seizure onset with enough confidence. To achieve this, this phase 2, called "invasive" EEG, uses electrodes directly in contact to the brain, which allows recordings of much greater precision. This involves placing electrodes or grids inside the skull over a specific region of the brain. Various techniques are available, including depth electrodes (intra-cerebral), epidural and subdural electrodes. Some of these "invasive" electrodes also allow determining with precision the function of each area of cortex, so that critical area can be avoided during surgery, thus preventing complications on motor, sensory or language functions.

 

TYPES OF SURGERY

  • Surgery is most commonly performed to treat partial epilepsy, since only one limited area of the brain is involved. Patients who have focal seizures originating in the anterior temporal lobe can benefit the most from surgery. This is because their seizures are restricted to an area of the brain that can be removed without damaging vital functions such as speech, memory and movement. The operation that is performed is called resection, or removal, of a specific area of the brain, and the most commonly performed is called anterior temporal lobe resection (temporal lobectomy). Other areas of brain tissue can also be removed depending upon the seizure source.
  • When seizures are severe and arise from an extensive area of one hemisphere, one approach is to remove a large part of one side of the brain (a hemispherectomy); Hemispherectomy is done to stop seizures for patients (usually children) who have hemiplegia (paralysis of one side of the body).
  • Another approach is to cut the nerve fibers connecting the two sides of the brain (a corpus callosotomy). Corpus callosotomy is done to reduce the frequency of disabling seizures for patients who have intractable generalized seizures that result in frequent falls and injuries.

 

RESULTS AND OUTCOME

 

After surgery, some patients may be completely free of seizures; others may find their seizures reduced by varying degrees. Some patients may have to continue to take medication, but their seizures are better controlled. Surgery may not be successful for some people, and rarely a second operation may be needed.

Successful epilepsy surgery will result in eliminating or significantly reducing the number of seizures. Seizure-free patients may still experience auras - warning feelings that may occur before a seizure - and take medication. However, while seizures couldn't be controlled with drugs before surgery, they can be controlled after surgery.

Success also depends on the specific individual situation. The more localized, or confined, the source of your seizure, the better the chances that surgery can make you seizure-free. In general, following anterior temporal lobectomy (the most commonly performed operation for epilepsy), over 80 percent show worthwhile improvement. This is somewhat variable depending on the results of the testing. For example, in cases where the results of EEG-video monitoring and MRI are in agreement, over 90% of patients become seizure-free.

 

CONCLUSIONS

While the majority of patients with epilepsy can be controlled by medications prescribed by their neurologists, those who are difficult to control should be referred to specialized centers, and this has been recommended by according to the National Association of Epilepsy Centers. Contrary to a common misconception, surgery for epilepsy is not experimental, and should not be considered a last resort. It is a well-accepted treatment for intractable epilepsy, and is used throughout the world.

 

ADDITIONAL READING

  • Wyllie E. The treatment of epilepsy: Principles and practice. 2nd edition. Baltimore: Williams & Wilkins, 1997.
  • Lüders HO. Epilepsy surgery. New York: Raven Press, 1991.
  • Benbadis SR, Chelune GJ, Stanford L, Comair Y. Outcome and complications of epilepsy surgery. In: Wyllie E (ed). The treatment of epilepsy: Principles and practice. 2nd edition. Baltimore: Williams & Wilkins, pp.1103-1118, 1997.
  • Benbadis SR. Evaluation for surgical treatment of partial epilepsy: an overview. Wisconsin Medical Journal 1995;94(9):500-504.
  • Benbadis SR. What can EEG-video monitoring do for you and your patients? Journal of the Florida Medical Association 1997;84:320-322.
  • Benbadis SR. Epilepsy explained. Healthline 1997;16(5):8-9.
  • Benbadis SR. The management of epilepsy. Healthline 1997;16(6):8-9.
  • Benbadis SR, Wyllie E. Evaluation of intractable seizures in children. In: Albright AL, Pollack IF, Adelson PD, (eds). Principle and practice of pediatric Neurosurgery. New York: Thieme. In press.
  • Benbadis SR. Invasive EEG. In: Lüders HO (ed). The epileptic seizure: pathophysiology and semiology. New York: Churchill Livingstone. In press.


Selim R. Benbadis, M.D. is Associate Professor and Director of the Comprehensive Epilepsy Program at the University of South Florida, in Tampa. He specializes in seizure disorders that are difficult to control, and has authored more than 40 scientific articles.
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