Who Should Be Evaluated for Epilepsy Surgery
What is epilepsy surgery?
Epilepsy surgery is a brain operation to control epileptic seizures. There are different types of operations for different types of epilepsy.
In epilepsy surgery, the surgeon removes the abnormal portion of brain that is causing the seizures. Brain tumors, vascular (blood vessel) abnormalities, old strokes, and congenital (inherited) irregularities might also be treated if they are believed to be causing the seizures.
Who is a candidate for epilepsy surgery?
In general, epilepsy surgery may be considered in people of any age. The best candidates for epilepsy surgery are:
- People with epileptic seizures that cannot be controlled satisfactorily with medication, and whose lives would be improved if seizures were controlled. (The definition of “satisfactory” control is different for every person.)
- People with a brain abnormality that can be identified as the cause of seizures. Some abnormalities such as brain tumors may need surgery even if seizures are well controlled with medication.
Which types of surgeries and procedures are considered?
Focal resective surgery is performed in people with partial epilepsy, in which seizures arise from a small part of the brain. Partial epilepsy may be caused by a scar from birth, injury or head trauma, brain tumors, arteriovenous vascular malformations (a tangle of blood vessels resulting in fewer than normal connections between capillaries), infections, or abnormal brain development.
In focal resective surgery, a small part of the brain is removed to preserve important neurological functions such as movement, sensation (feeling), speech, and memory. The most common location of this surgery is in the temporal lobe (under the temple).
Hemispherectomy is performed in people with abnormalities of one hemisphere (side) of the brain. Conditions such as Sturge-Weber disease, Rasmussen’s encephalitis, hemimegalencephaly, or perinatal stroke may injure a large area on just one side of the brain. People with these disorders usually have severe neurologic problems, such as paralysis and loss of feeling on one side of the body. With this procedure, a portion of the damaged brain is removed, and the rest of the hemisphere is disconnected from the “good” portions of the brain to keep the seizures from spreading.
Callosotomy involves cutting part of the corpus callosum, a large bundle of nerve fibers that connect the two sides of the brain. The goal is to keep seizures from spreading from one side of the brain to the other. Callosotomy is usually performed in people with severe generalized tonic (stiffening) or atonic (limp) seizures that cause falling and injuries ("drop attacks").
Subdural electrode insertion involves placing electrodes directly in contact with the brain in order to better pinpoint the region(s) of the brain that cause seizures. They also can be used to stimulate the underlying brain tissue, and verify the presence of cortex that supports important motor or language function. This technique is especially useful in patients who have medically intractable (stubborn) epilepsy and require functional brain mapping in addition to seizure onset information.
Stereoelectroencephalography (SEEG) is a “less invasive” method for mapping seizures in which thin recording probes are precisely placed into deep regions in the brain. The patient usually has several studies before the probes are placed, including MRI, PET scans, and magnetoencephalogram (MEG). This technique allows safe, precise, and three-dimensional mapping of seizure activity in brain regions that cannot be seen with other mapping techniques. It is especially useful for patients who need recordings from deep areas in the brain and in patients with “normal” MRI.
Vagal nerve stimulation involves placing an electrode on the left vagus nerve and a generator under the skin over the left chest. The device is then programmed to deliver periodic electrical impulses to the vagus nerve, which are then sent via the brainstem to the cerebral cortex. The device may reduce seizures in approximately 40 to 50 percent of patients. It is generally intended as an option for patients who cannot have resective surgery.
Responsive neurostimulation is an investigational technique being studied at Cleveland Clinic. This treatment identifies seizure activity with an electrode and a computer implanted in the patient’s brain. Once a seizure occurs, the device fires an electrical impulse into the region of the brain responsible for the seizure.
What is the evaluation process for epilepsy surgery?
A number of steps are necessary to identify the location and cause of the seizures, and to determine the best treatment:
- A neurologist will perform a medical history and neurological examination.
- Electroencephalogram (EEG) is a "brain wave" test that detects abnormal areas that may cause seizures.
- Magnetic resonance imaging (MRI) gives a detailed picture of the inside of the brain. MRI may help identify the cause and location of the seizures.
- Adjustments or changes in medication may be made before surgery is considered. Sometimes, just adjusting medications can control seizures. Usually, at least three medicines are tried before considering epilepsy surgery. Blood tests are necessary to adjust medication levels for best effect.
- Video-EEG monitoring is done while the patient stays in the hospital for five to seven days. EEG is performed continuously, and medications are reduced so that seizures can be recorded. The monitoring is taped and the seizures are analyzed to gain information about where they start.
- Other tests give information about how well different parts of the brain are working. These tests include a positron emission tomography (PET) scan, magnetoencephalogram (MEG), ictal SPECT, functional MRI (fMRI), neuropsychological testing (memory, language, and thinking), and an intracarotid amobarbital test, in which half the brain is put to sleep for a few minutes to test the function of the other side. Psychiatric evaluation may reveal other conditions, such as depression, which also need to be treated.
- In some cases, EEG electrodes must be put directly into or on the surface of the brain through surgery to find the source of the seizures and to map out important brain functions that should be spared.
Recovery and Outlook
How well does epilepsy surgery work?
The results of surgery depend on the cause and location of the seizures. Some types of epilepsy may have a 60 percent to 90 percent chance of becoming seizure-free after surgery. In other cases, the goal of surgery is to reduce the number of seizures or to reduce injuries caused by seizures. The epilepsy surgery evaluation is necessary to carefully determine the potential benefits and risks in each case.