|
Several tests are performed as part of the evaluation before the recommendations for surgery are made. Tests that are needed to better localize the seizure onset zone include video-EEG monitoring, magnetic resonance imaging (MRI), single photon positron emission computerized tomography (SPECT), and positron emission tomography (PET).
Video-EEG: Patients are admitted to the hospital for continuous observation  with video cameras, to record the symptoms of the seizures, and electroencephalography (EEG), to monitor the electrical activity of the brain during the seizures. This test is important in determining whether all seizures originate in one area of the brain and to localize the seizure onset zone. Abnormal electrical activity can also occur between seizures, and is registered by computers for review.
SPECT: During a seizure recorded in the video-EEG monitoring, a small amount of radioactive tracer can be injected into the vein, which is taken up in the part of the brain that is most involved in the seizure. A second study is then performed when the patient is not having a seizure for comparison.
 MRI: MRI can detect structural abnormalities in the brain that can cause seizures. MRI facilities are available at the Research Imaging Center, University Hospital and Audie Murphy Veterans’ Association Hospital.
PET: These scans generate pictures that measure the metabolism of glucose or blood flow indicating the health of brain regions in patients when they are not having seizures. The Research Imaging Center, University Health System and Cancer Therapy and Research Centers all provide PET imaging.
Other tests are employed to evaluate the risk of surgery:
Neuropsychological testing allows the assessment of cognitive functioning, particularly for memory and language. These tests are carried out before and after epilepsy surgery to evaluate potential risks posed by the surgery and cognitive outcome.
The IAP (intracarotid amobarbital procedure) is performed by a neuroradiologist, who injects either carotid artery, thus causing one half of the brain to fall asleep. This allows the selective testing of language and memory functioning in each half of the brain.
Functional PET and MRI, which are important for the mapping of motor, sensory and language areas, are available at the Research Imaging Center and University Hospital. The IAP and functional neuroimaging studies are particularly important for the epilepsy surgeon to plan for the safety of the patient during surgery.
Epilepsy Surgery Case Conference: The clinical information gathered on patients who have  completed the presurgical evaluation is presented by the epilepsy specialists in a multidisciplinary conference, consisting of neurologists, neurosurgeons, neuroimaging specialists, psychiatrists and neuropsychologists. The multidisciplinary team decides upon the intervention most beneficial to the patient. The patients and family members are then scheduled by the Epilepsy Surgery Case Manager to meet the neurosurgeon in the Epilepsy Surgery Clinic.
Epilepsy Surgery Clinic: Patients are examined by the neurosurgeon and the risks and benefits of the proposed surgery are discussed. Most patients undergo blood tests and an exam by the anesthesiologist. They are scheduled for the surgery.
Surgery: Epilepsy surgery is an extremely delicate procedure lasting several hours. Most patients undergo surgery under general anesthesia. Others may be awake during the surgical procedure for mapping of language functions in the operating room, a precaution aiming to reduce any risk of damage to the speech areas of the brain. Some patients may require a second video-EEG evaluation with electrodes placed directly onto the surface of the brain. These subdural or depth electrodes can help to further localize the area of the seizure onset. Furthermore, subdural electrodes can aid the epilepsy team to better map out functionally important areas of the brain. After monitoring, the electrodes are removed and the surgery is performed. The vagal nerve stimulator, on the other hand, is implanted as an outpatient procedure.
 Postoperative Care: Patients generally require three to five days of recovery following surgery. They are discharged on seizure medications which they continue to take as directed by the epilepsy specialists.
Epilepsy Surgery Outcomes: The patients are seen in follow-up in the Epilepsy Surgery Clinic several times in the first two years. Six months after surgery, a postoperative MRI and EEG are performed. If patients are seizure free, medication doses are gradually lowered. One year after surgery, patients undergo neuropsychological testing to detect any changes in memory or language functioning related to their surgery. If patients remain seizure free after two years, seizure medications are withdrawn.
In a retrospective analysis of one-year seizure outcome of over 130 patients undergoing resective surgeries, 80% of the patients underwent temporal lobe resections and the remainder had surgeries in brain regions outside of the temporal lobe. Seizure outcome was categorized according to the modified Engel classification system, with Class 1 and 2 outcomes grouped as favorable (seizure free or rare breakthrough seizures), and Class 3 and 4 outcomes less favorable (may be reduced but persistent or not affected by surgery). Class 1/2 outcomes were achieved in 82% of the temporal lobe resections compared to 63% of extratemporal resections. In order to spare important neurological functions, it is often difficult to remove the entire seizure onset zone with extratemporal resections. Nonetheless, these data are comparable to other major epilepsy surgery centers in the United States and Canada.
Table 1. Seizure outcomes of resective surgery by STCEC (Yaltho et al., Epilepsia, 2007;48(S6):152)
The main complications of resective surgery, including stroke or infection, range between 3-6%, depending upon the need to implant electrode arrays or grids.
|
