Epilepsy

Description

Surgery

Surgical techniques to remove injured brain tissue may be appropriate for many patients with epilepsy. The surgeon's goal is to remove only the damaged tissue in order to prevent seizures and to avoid healthy brain tissue. Surgical techniques for reaching these goals have improved significantly over the past decades due to advances in imaging and monitoring, new surgical techniques, and a better understanding of the brain and epilepsy.

Tests to Determine if Surgery Is Indicated

A number of tests using imaging and electroencephalography (EEG) can determine if surgery is an option.

• The general approach is to first use long-term EEG monitoring to locate the brain tissue that triggers the epileptic event.
• Advanced imaging techniques can provide valuable additional information. They include functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG), positron emission tomography (PET) or single-photon emission computer tomography (SPECT) scans.

If the imaging tests indicate that more than one site is involved or their results conflict, then more invasive monitoring of the brain may be required, although the newer imaging tests are proving to be very accurate tools. If such tests pinpoint a specific area in the brain as the location for seizures, then surgery is possible. MEG, for example, is now approved for imaging parts of the brain involved with motor control, sensation, and language function, and may become important in evaluating patients who are likely candidates for surgery. The physician will also examine the test results to determine if the offending nerve cells perform vital functions and try to predict surgical outcome in certain cases.

The major areas of the brain have one or more specific functions.

Temporal Lobectomy

The most common surgical procedure for epilepsy is temporal lobectomy, which is performed when epilepsy occurs in the temporal lobe. (Surgery is not as successful in epilepsies that occur in the frontal lobe.) It involves removing small portions from the hippocampus, a portion of the brain that is involved in memory processing and is part of the limbic system, an emotional center.

Click the icon to see an image of the limbic system of the brain.

Candidates. A typical candidate for this surgery is an adolescent or young adult with complex partial seizures that began between age five and 10, and although the seizures were often in remission, they eventually became intractable.

Young children may be more difficult candidates because they often have injured areas outside the temporal lobes. Nevertheless, surgery can be very successful in many children, even if more than one area is involved.

Success Rates. New imaging techniques are dramatically improving the success rates of temporal lobe surgery. A 2000 literature review estimates that more than 70% to 90% of appropriate patients remain seizure-free after temporal lobectomy. And in an important 2002 comparison of surgery versus medication, after an average of nearly five years, 44.6% of the surgical group was continuously free of seizures versus only 4.3% of those taking medications alone. Patients still need to take medications, even if seizures are very infrequent. Cure is not always possible, and some patients may still experience some seizures. Double vision is very common after the operation, but it is nearly always temporary and resolves within a few months.

Studies are further indicating that temporal lobe surgery improves quality of life and may even prolong survival. Some experts theorize that surgery might stabilize parts of the brain that influence heart rate and may reduce the risk of sudden death, a rare complication of epilepsy.

Effects on Mental Functioning. Although surgery on the left temporal lobe does not impair intelligence to any significant degree, studies on the effects of mental functioning and behavior are unclear:

• One study reported that 10% of patients experienced significant decline in language abilities while another 9% reported significant improvement. In the study, about 16% reported improvement in nonverbal mental functions.
• In another study of children, surgery improved behavior in 31% of the patients and mental function in 25%. (Detrimental changes in personality, emotions, or behavior are uncommon.)

In general, surgical effects on mental functioning and behavior depend on the extent and location of the surgical area.

Lesionectomy

Lesionectomy is a procedure that removes specifically abnormal tissues in certain conditions, such as the following:

• Cavernous angiomas (abnormal clusters of blood vessels).
• Low-grade brain tumors.
• Cortical dysplasias. (This is an abnormality in fetal development in which the normal migration of nerve cells is altered for some reason.)

This local surgery, which can cure the patient's epilepsy, has become possible with the advent of advanced imaging techniques such as MRI.

Other Surgeries

Other surgical procedures called hemispherectomy and corpus callosotomy offer hope for specific patients. They include infants and young children with catastrophic seizures that occur in one or part of a hemisphere and for patients whose seizures are due to specific structural brain abnormalities or tumors.

Hemispherectomy. Hemispherectomy is the removal of half the brain, leaving the deep structures intact. Surgery can take 12 hours and there is always some paralysis on one side of the body. There is also a small risk for hydrocephalus, coma, or even death. Quality of life is almost always improved, however, and the surgery does not reduce intelligence.

Corpus Callosotomy. Corpus callosotomy involves cutting the nerve fibers that connect one side of the brain to another. It does not remove brain tissue. It may be done in two stages. In the first there is a partial separation. If seizures continue, then the surgeon may perform a complete separation. This surgery can reduce (although not entirely stop) uncontrolled tonic clonic seizures. The procedure has been used in patients with specific syndromes, such as Lennox-Gastaut syndrome. The procedure can have very severe complications, however.

Vagus Nerve Stimulation (VNS) and Other Neurostimulation Procedures

Electrical stimulation of areas in the brain that affect epilepsy is helping many patients with refractory epilepsy. Vagus nerve stimulation (VNS), an electrical stimulation of the vagus nerve, is now an accepted therapy for severe epilepsy that does not respond to AEDs. The two vagus nerves are the longest nerves in the body. They run along each side of the neck, then down the esophagus to the gastrointestinal tract. They affect swallowing, speech, and many other functions. They also appear to connect to parts of the brain that are involved with seizures. The procedure is as follows:

Click the icon to see a depiction of epilepsy treatment.

• A battery-powered device similar to a pacemaker is implanted under the skin in the upper left of the chest.
• A lead is then attached to the left vagus nerve in the lower part of the neck.
• The neurologist programs the device to deliver mild electrical stimulation to the vagus nerve. (Patients may also pass a magnet over the device to give it an extra dose if they sense a seizure coming on. This appears to help about 25% to 30% of patients.)
• The batteries wear out after three to five years and need to be removed and replaced by a simple surgical procedure.

An investigatory approach called deep brain stimulation targets the thalamus (which relays pain, temperature, and touch sensations to the brain). Early small studies are promising.

Candidates. The American Academy of Neurology now recommends VNS for the following:

• Patients who are over 12 years old, and
• Have partial seizures that do not respond to medication, and
• Are not appropriate candidates for surgery.

Evidence is accumulating, however, to indicate that VNS is effective and safe for many patients of all ages and for refractory epilepsy of many types.

Success Rates. Studies are reporting that the procedure reduces seizures within four months by up to 50% and even more in many patients. Studies report that it has been effective for longer than seven years. In one study that followed patients for a year, the benefits of VNS appeared to even increase over time.

Complications. It should be noted that vagus stimulation does not eliminate seizures in most patients and is still somewhat invasive. Vagus stimulation can cause shortness of breath, hoarseness, sore throat, coughing, ear and throat pain, or nausea and vomiting. These side effects can be reduced or eliminated by reducing the intensity of stimulation. Some studies suggest that the treatment causes adverse changes in breathing during sleep and may cause lung function deterioration in people with existing lung disease. People who have obstructive sleep apnea also should be cautious about this procedure. Turning off the VNS (for example before an MRI or surgery) may increase the risk for status epilepticus. (It should be noted that VNS may also be helpful for treating status epilepticus in some patients.)

Experimental Procedures

Gamma Knife Surgery. A device called a gamma knife delivers very focused beams of radiation. Typically used for brain tumors, it is now under investigation for temporal lobe epilepsy and for seizures due to cavernous malformations.