Surgery for epilepsy is considered when seizures are frequent enough and/or severe enough to significantly interfere with a person's ability to function at full capacity despite appropriate anti-seizure medications. Of the different kinds of epilepsies, partial (or focal) epilepsy, such as temporal lobe epilepsy, have the best surgical outcomes.
Patients with progressive neurological disease or other significant medical problems such as cancer or heart disease usually are not considered for epilepsy surgery. Patients of any age, including infants, may be considered for surgery if other criteria are met.
A team of neurologists, neurosurgeons, nurse specialists and neuropsychologists participates in evaluating each patient being considered for epilepsy surgery.
The evaluation process includes an extensive interview concerning the patient's past history of epilepsy, as well as physical and neurologic examinations. Additionally, several diagnostic studies are conducted, including a baseline EEG, CT Scan and/or MRI, neuropsychological evaluation, and intensive seizure monitoring with simultaneous video and EEG recording. Some patients may additionally require video/EEG monitoring using electrodes placed surgically within or around the brain itself before the final seizure surgery can be performed. The need for such electrodes is considered on an individual basis. Other examinations, also considered on an individual basis, include the Wada test, PET or SPECT scans, and psychiatric evaluations.
The EEG (electroencephalogram) involves recording a patient's brain waves in order to record and analyze the seizure discharges. CT (computerized tomographic) and MRI (magnetic resonance imaging) scans can help point to where a patient's seizures originate. Magnetic resonance based techniques that are in use or under development can help assess not only brain structure, but also brain function. PET (positron emission tomographic) and SPECT (single photon emission computed tomographic) scans test brain metabolism, chemistry or blood flow with the use of specially prepared radioisotopes that have been found safe for medical diagnostic use.
The basic types of epilepsy surgery are:
- Focal resection
- Hemispherectomy
- Corpus callosum section
Focal resection (lobectomy) involves removing the portion of the brain where seizures originate. The temporal lobe is the most common region involved in this type of surgery. This procedure is effective only if seizures originate consistently from one location in the brain. It is therefore essential to record several seizures to judge the site of seizure origin. Depth electrodes,or subdural and/or epidural electrodes, may be implanted to localize the site more precisely. Depth electrodes consist of fine wires placed deep within the brain. Epidural or subdural electrodes consist of small metal disks placed on the surface of the brain. The type of electrode used will depend on the special circumstances of the individual patient. The specific risks of the surgery depend on the type of procedure being considered.
Hemispherectomy is the removal of the majority of one cerebral hemisphere. Clearly, this is a radical procedure, and it usually performed on children with severe and very frequent seizures that, although confined primarily to one side of the brain, continue to worsen in spite of medication. Patients typically are partially or completely paralyzed on the side of the body opposite to the diseased hemisphere. In this situation, experience has shown that less extensive surgery would not be useful. Suitable for only a very few patients, hemispherectomy has proven to be a very successful type of seizure surgery but is associated with significant risks. The severe one-sided weakness present before surgery is likely to persist after surgery.
Corpus callosum section, also called corpus callosotomy, is rarely performed today. The neurosurgeon severs the fibers connecting the two halves (hemispheres) of the brain. This disconnection does not usually stop the patient from having seizures. In fact, certain kinds of localized seizures may become more frequent. The procedure does help to stop the spread of seizures, however, preventing them from involving the entire brain. This confinement of seizure activity to one side of the brain may protect the patient from injury caused by loss of consciousness and seizure-related falls. Patients who undergo this procedure generally are not candidates for other types of epilepsy surgery because their seizures usually originate in more than one area of the brain. After surgery, the patient may experience temporary or permanent limitations with speech, movement of certain body parts, or behavior. It is important for patients and their families to understand that these risks exist, and to understand that this surgery is not performed with hope of curing the seizures, but rather with hope of helping to reduce their severity.
