Surgery for Medically Intractable Epiepsy

For about 70 percent of people with epilepsy, seizures can be controlled with anti-epileptic drugs (AEDs). When seizures are not well managed by medication (as indicated by the severity or frequency of seizures), the condition is referred to as medically intractable epilepsy.

Surgery generally is reserved for these most severe cases of epilepsy. Candidates for surgery at the University Comprehensive Epilepsy Center are evaluated carefully by a multidisciplinary team spanning the disciplines of neurology/epileptology, neurosurgery, neuropsychology, neuroradiology, neurophysiology, advanced practice nursing, social work, nutrition, and rehabilitation therapy. This team actively involves patients and their families in the patient’s treatment plan.

Pre-Surgical Tests

The surgical team gathers as much information as possible about the patient’s condition and, significantly, the unique structure of his or her brain prior to the operation. Of particular concern is pinpointing the precise location of the epileptic focus, the area in the brain where seizures originate. Continuous video EEG monitoring, the Wada test, functional MRI studies, and other tests described in Diagnostic Tests for Epilepsy are valuable tools prior to surgery.

Intraoperative EEG Monitoring and Intraopertive MRI

During epilepsy operations, intraoperative EEG monitoring may be performed to provide objective information about the anesthetized patient. This gives the surgeons immediate feedback on signs of impending risk and enables them to feel comfortable with a greater degree of surgical intervention than they would have without intraoperative monitoring.

Normally, a patient undergoes a variety of scans and tests prior to surgery. Surgeons use the data they obtain from the tests to pinpoint the areas of the brain requiring surgery. While many of these tests are extremely accurate, a higher degree of accuracy is obtained when the tests are actually done during the surgery. The accuracy is increased because in addition to being more up-to-date and recent, the tests are done on the patient while the patient is in the exact position for surgery. In addition, many of these tests provide on-going feedback throughout the operation, giving the surgeon information that enables more informed decisions to be made regarding the patient's care.

Another technique uses MRI technology to obtain images of the brain during surgery. In intraoperative MRI, real-time visualization allows surgeons to confirm the location of lesions, plan and reconfirm the optimal surgical approach, and verify complete lesion removal prior to closure.

Conventional surgical navigation systems rely on images obtained prior to surgery and cannot account for movement of the brain during the surgery that could result simply from exposure or from tissue removal. With the use of MRI images obtained during various points in the surgery, the navigation system continuously adjusts to account for any brain shift, thereby minimizing harm to healthy and/or eloquent areas of the brain.

University Hospital is one of two hospitals in the world currently to utilize a compact OR-based MRI system (PoleStar N-10) that successfully addresses the problems associated with early versions of intraoperative MRI systems, including cumbersome design, limited application, and high cost.

Surgical Options

The type of epilepsy a patient has, in conjunction with pre-operative testing, determines which type of surgery will be performed. Because precise location of the epileptic focus is so important to an operation’s success, the Center has developed expertise in Functional Image Guided Surgery (FIGS). FIGS combines Functional MRI with frameless stereotactic surgery to create a precise, detailed "road map" for the surgeon to follow. At every second of the procedure, the surgeon knows the proximity of healthy brain tissue and therefore can avoid removing or damaging it.

Surgical procedures offered at the Center include:

1. Temporal and extratemporal cortical resections for adults and children. Some seizures originate from a specific point in the brain, an area referred to as the seizure focus. This area varies from person to person. The technology available today–continuous video EEG monitoring, MRI, and SPECT–often enables epileptologists to pinpoint the seizure focus. When surgery is indicated, a neurosurgeon operates to remove the affected brain tissue. The most common resection is for people with epilepsy located at the temporal lobe, at the brain’s outer lower region. The surgery results in reduction or elimination of seizure activity between 70 and 90 percent of the time.
   
   
2. Corpus callosotomy. When seizures originate in one half of the brain and spread to the other, a corpus callosotomy can be performed to sever the neural connections between the brain’s two hemispheres. This surgery usually is performed on children.
   
   This "disconnection" is not a cure, but it can reduce the severity of generalized seizures. Corpus callosotomy can also keep seizures from spreading to other areas of the brain. However, partial seizures may increase after surgery.
   
   
3. Hemispherectomy. As the name suggests, this surgery involves removal of about half of the brain, or a hemisphere. Hemispherectomy usually is reserved for children with severe, frequent, and often life-threatening epilepsy that cannot be controlled by medication. The seizures originate from one side of the brain, and typically, the child has some degree of paralysis on the opposite side of the body.
   
   Removing half of someone’s brain is, indeed, a radical concept, and there may be some very serious complications, including fluid build-up in the brain, infection, and coma. There is permanent loss of hand mobility on the side opposite of the removed hemisphere, and vision also may be affected. But doctors have found that for many of these children, hemispherectomy significantly or completely controls seizures and enables the youngsters to function well with improved behavior and intelligence. Especially in younger children, the remaining half of the brain compensates for the missing half.
   
   
4. Vagal Nerve Stimulation. Unlike the surgeries described above, this operation is not performed on the brain. The body has two vagus nerves, one that travels up the left side of the neck and one on the right. One of the left nerve’s jobs is to relay information to areas of the brain that are believed to produce seizures. When this nerve is stimulated by a low level of electrical current, some people find that their seizures are less frequent or less severe. Vagal nerve stimulation has most commonly been used for patients with partial seizures.
   
   A small, battery-operated device called a vagal nerve stimulator can be placed in a person’s body. It can be programmed to deliver stimulation at regular intervals, or it can be activated with a magnet when a patient experiences an aura. The surgery involves implanting the device’s generator under the skin in the patient’s upper left chest. A connecting wire is guided under the skin and attached to the vagus nerve, which is located on the left side of the neck. The operation lasts about two hours, and a common temporary side effect of the surgery is hoarseness, as the vagus nerve is located near the voice box. Sometimes people experience coughing or a tingling in their throat when the stimulator is activated; adjusting the amount of current can remedy this side effect.
   
   The vagal nerve stimulator’s effectiveness varies. Most patients can expect a 50 percent reduction in seizures, while others experience better or worse results. The device is not considered to be a cure, so patients generally continue taking anti-epileptic medication. In cases where the stimulator has proven highly effective, the doctor may decide that a patient’s medications can be reduced.

An incision is made in the lower neck to place an electrode around the vagus nerve. The stimulator is implanted under the skin in the chest wall through a second incision. Similar to a heart pacemaker, the stimulator emits an electrical impulse every five minutes that stimulates the vagus nerve.

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