Anti-epileptic drug therapy is effective in approximately two-thirds of people with epilepsy, implying that one-in-three do not obtain good seizure control or have unacceptable side effects from medications. The concept of good seizure control is elusive. How long must a person go without a seizure before control is considered good? This is a matter of individual opinion. In some states, an individual cannot obtain a driver’s license if he or she has had a seizure within one year. Good control might therefore represent being seizure-free for one year. The standard is often set too low, with physicians who believe that a seizure or two every month or even every few months is not “too bad.” But such a seizure frequency can have a major impact on the quality of life of people with epilepsy. Conceptually, seizures are not in good control if their occurrence, at any numerical frequency, restricts the quality of life. Part of the challenge of epilepsy specialists is to encourage treating physicians and patients to strive for better control of seizures, and not to be complacent about the limitations imposed by occasional seizures.
Candidates for Epilepsy Surgery
Some people who cannot be controlled with medications are candidates for surgery to cure their epilepsy. Counts of potentially eligible candidates range in the 20,000 - 100,000 range in the United States. Since only a few thousand operations are done each year, it is apparent that surgery for epilepsy is under-utilized. This is an issue of education, availability of epilepsy treatment resources and expense. Epilepsy surgery is costly, with the evaluation process, surgery, and recovery phase typically costing more than $50,000 in the United States. However, economic analyses taking into account the direct and indirect medical costs of uncontrolled seizures indicate that the money can be recovered over several years. Most insurance agencies, including Medicare, State Medical Assistance programs and private carriers, pay for epilepsy surgery in qualified candidates.
Good candidates for epilepsy surgery meet the following criteria:
One key to successful epilepsy surgery is accurate localization of the seizure focus, where seizures apparently start. Secondarily generalized tonic-clonic seizures will stop if the focal point of origin is removed. Temporal lobe is the most seizure-prone of the four lobes of the brain, although surgery can be performed in any lobe of the brain. Seizures that emanate from both temporal lobes are not amenable to surgery, because removal of both temporal lobes would create severe and permanent memory problems.
EEG (electroencephalogram, brain waves) can help to localize the seizure focus, by demonstrating abnormal electrical activity. Most EEGs are obtained between seizures. With a single EEG, abnormalities are seen in about half of people with epilepsy, but the percentage of significant findings increases with repeated EEG recordings, approaching 80% after four EEGs. Between seizures, EEGs can show spikes or sharp waves. These are pointy waveforms reflecting hyper-excitability of the underlying brain. Surgical candidates usually undergo video-EEG monitoring in a hospital epilepsy monitoring unit in order to record brain activity and behavior during several seizures. The hope is to find that all seizures come from the same region (the seizure focus), and that it is located in a safe place for surgery. The most common location for a seizure focus is in the inner portions of the temporal lobe, deep to the left or right ear. Inpatient video-EEG monitoring can take from 1 to 14 days, depending on how soon seizures occur. Medications may be temporarily withheld to provoke seizures for recording. A personal account of video-EEG monitoring can be read here.
Magnetic resonance imaging (MRI) or computed tomography (CT) provide structural images of brain. MRI shows greater detail than does CT. These tests may show an underlying cause of the seizures, for example, abnormal blood vessels, an old stroke, scarring from a prior infection, a birth defect (called dysplasia), a tumor, or a form of scarring in the temporal lobe called mesial temporal sclerosis. However, MRIs fail to disclose a cause of epilepsy in more than half of cases. Every serious candidate for epilepsy surgery needs a high quality brain MRI.
Positron emission tomography (PET) scan is a neuroimaging procedure that looks at glucose (sugar) consumption in the brain. Glucose is the energy supply for the brain. The majority of people with a temporal lobe seizure focus demonstrate low glucose consumption in the region of a seizure focus. A PET scan is not required for every epilepsy surgery evaluation, but it can be helpful where the location of the seizure focus remains unclear after video-EEG monitoring and MRI.
Neuropsychological tests are performed to determine whether a patient has speech or comprehension impairments, usually reflecting injury to the dominant left brain (in right-handers), or picture, face and shape memory impairments, which usually reflects right brain damage. Neuropsychological testing also can screen for depression, which is highly prevalent in this population. Psychosocial adjustment after epilepsy surgery is important to the success of the procedure, since the goal is improvement of quality of life, rather than just elimination of seizures.
Other specialized tests, such as magnetoencephalograpy (MEG), magnetic resonance spectroscopy and cerebral angiography are useful in some particular circumstances, but not required in all cases.
Some patients appear to be surgical candidates, but the seizure focus cannot be precisely localized with the above tests. These individuals may undergo invasive monitoring with electrode wires placed into regions of brain suspected of harboring a seizure focus. Brain electrodes come in the form of thin wires to be be inserted into brain tissue or plastic sheets of electrodes, called strips or grids, to be place on top of brain tissue (figure). Each type is useful in different circumstances. Brain electrodes often show where seizures originate, but use of these electrodes does entail some risk for bleeding, infection or injury to brain. Grids can be used to electrically stimulate the area underneath the contact points and map the function of the brain at that region. This procedure is used when the seizure focus is likely very close to a speech or sensory-motor area of brain and precise delineation of boundaries is required. The grid usually is left in place for about a week. When it is removed, the operation to remove the seizure focus is done during the same procedure. Only a few percent of patients with epilepsy undergoing surgery will need mapping with a grid.
The Wada intracarotid hemispheric dominance test is done to localize speech and memory functions in candidates for epilepsy surgery. A portion of the brain on the left or the right is anesthetized by injection of a quick-acting sedative into the internal carotid artery, via a catheter placed in the femoral vein at the groin. Speech and memory then are tested. It can be thought of as a “dry run” for surgery. Surgery can be performed on the temporal lobe of the speech-dominant side, but not as much brain can safely be removed as on the non-dominant side. Extensive amnesia after injecting one internal carotid artery is a danger signal for surgery, because it suggests that there could be severe memory problems after the operation. The Wada test usually does not require overnight hospitalization.
Upon completion of evaluation to localize the seizure focus, the patient, family, and doctor will discuss whether to proceed with surgery. Epilepsy surgery is elective; no person should be pushed into having epilepsy surgery. Alternatives include continuing with conventional anti-epileptic medications, trying new medications, vagus nerve stimulation, deep brain stimulation, the ketogenic diet, and other therapies currently being researched. Surgery may, however, be the most effective way to eliminate seizures in people whose seizures are not controlled by medications.
Temporal Lobectomy Surgical Procedure
Removal of the inner seizure-prone portions of the left or right temporal lobe is called partial temporal lobectomy, and it is the most commonly performed operation for epilepsy. After the patient is positioned and asleep, the surgery begins. A patch of hair over the temple is shaved, but it is not necessary to shave the entire head (some prefer a full shave to an uneven trimming). Skin is cut in a “C”-shaped partial circle above the ear. Several nickel-sized holes are drilled in a circular pattern. A bone-saw cuts between the holes to remove a circle of bone about the circumference of a coffee cup. At the end of the procedure, this bone will be hard-wired back in place and eventually will calcify to seal to the skull. The membrane over the brain, the dura mater, then is opened, exposing the temporal lobe. Portions of the temporal lobe are removed by suction, since the brain has a soft consistency. Different surgeons use different techniques and approaches, depending upon preference and training, but no one technique is proven superior to the others. The amount usually removed ranges between the size of a golf ball and a small lemon, representing less than half the volume of the temporal lobe (figure).
Portion of brain removed in temporal lobectomy. The patient is lying with right side up, top of the temporal lobe forward. Finger at top gives perspective as to size.
The portion of brain removed never grows back. The space that it previously occupied immediately fills with the cerebrospinal fluid surrounding the brain. Patients sometimes wonder why replacing a seizure-producing scar with a surgical scar is beneficial. The reason is that not all scars are alike. The “clean” scar left by neurosurgery rarely leads to seizures. Closure of the surgical field occurs in reverse order to the opening.
Patients typically are in the operating room and recovery room for 6-8 hours, sometimes longer, with the operation itself requiring about 3-4 hours. The family should be prepared for the patient to be disoriented for a day postoperatively. Headache is common, but over-medication is avoided to allow the patient to wake up. Common postoperative side effects in the first few days include nausea from the anesthesia, a sore throat from the breathing tube in the operating room, swelling and bruising of the forehead and around the eye on the side of surgery. The swelling increases to a peak 2-4 days after surgery. An overnight stay in intensive care is common to provide close nursing monitoring. By 2-3 days after surgery, most patients are able to sit in a chair, walk with assistance, and eat. Seizure medicines may have to be given by vein until pills can be swallowed. Since not every medicine has an intravenous form, a temporary switch to one that does may be required. Hospital discharge happens 3-7 days after surgery. Patients should plan on staying at home with assistance for a week, and staying off work or heavy activities for a month. A few patients have persistent headache or fatigue, and require 2-3 months post-operative rest.
Complications of temporal lobectomy occur in about 2% of patients (one-in-fifty) who have this surgery. Complications can be serious, including as a partial list:
Less serious complications occur more often, such as deterioration of word-finding ability for a few months after surgery, pain-itching around the skin scar (especially as it heals), infection of the surgical site, skull indentations or other cosmetic defects, persistent headaches, minor loss of upper peripheral vision on the side opposite the surgery, drooping of eyelid or forehead on the surgical side, transient depression, and a variety of other problems.
Seizures occasionally flare up for 1-2 months after seizure surgery, as the brain heals. Seizures during the postoperative months do not necessarily mean that the operation was a failure, since seizures may settle down with healing. You should discuss the potential benefits and risks of surgery with your surgeon, and give what is known as “informed consent” for the procedure if you agreed to have surgery.
Epilepsy surgery eliminates disabling seizures about two-thirds of the time, and produces partial improvement in an additional percentage. Patients may be completely cured of their epilepsy and be able to go off all medications, typically a year or two after the surgery. Others still require medication. Benefit of surgery may fall short of a complete cure - patients may still have occasional auras (warnings) or rare breakthrough seizures at times of great stress. Some patients do not respond favorably to seizure surgery, usually because not all of the focus could be removed or because the seizures were in fact located at several places in the brain (multifocal).
Other Surgical Procedures
Other specialized procedures are performed less often than is partial temporal lobectomy. The corpus callosum resection (colloquially known as the split-brain operation,) separates the major band of fibers inter-connecting the left and the right hemisphere of brain. This rarely cures seizures, but may slow down spread of the seizures and allow time for a warning in time to sit down. The split-brain operation can be viewed as a procedure to prevent injuries from seizures, rather than a cure for seizures.
Hemispherectomy entails removal of the majority of one hemisphere (half) of the brain. This radical procedure is employed in individuals, usually children, who have severe damage to one hemisphere. Candidates may suffer from a type of encephalitis called Rasmussen’s encephalitis, in which the local damage to a hemisphere is progressive over years. Although the children are initially weak on the side of the body opposite surgery after the procedure, function usually partially recovers. Recovery is more complete for younger children (< age 6) than for those in the teens or beyond. Children who recover well from a hemispherectomy grow up with only a clumsy hand and a limp.
Lesionectomy involves removal of a lesion, which is a visible structural abnormality causing the seizures, for example, a small tumor or an abnormal blood vessel. This procedure can be very effective in cases where the whole lesion and a small surrounding margin of brain can safely be removed.
Epilepsy surgery is a specialized type of neurosurgery. It is been performed at Academic Epilepsy Centers where a multidisciplinary team can evaluate and treat the patient. A list of such centers, certified by the National Association of Epilepsy Centers, can be found at www.naec-epilepsy.org.
Epilepsy surgery is sometimes a good option for people whose seizures cannot be controlled by medication. Temporal lobectomy is the most common epilepsy surgery procedure and lesionectomy the next. Each of these first requires tests to localize the place of origin of seizures in the brain. In properly selected candidates, epilepsy surgery can eliminate or greatly reduce seizures, and thereby allow reduction of seizure medication. Unfortunately, the success rate is not 100% and serious complications occur in about 1 in 50 people undergoing surgery for their epilepsy. Epilepsy surgery is always elective and it is not for everyone, but sometimes it is the best way to control seizures and improve the quality of life. Videos on epilepsy surgery and interviews with people who have had surgery can be viewed here .
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