How you prepare

If you're a possible candidate for epilepsy surgery, you will work with a medical team at a specialized epilepsy center. Your team will conduct several tests to determine your eligibility for surgery, identify the appropriate surgical site and understand in detail how that particular region of your brain functions. Some of these tests are performed as outpatient procedures, while others require a hospital stay.

Evaluations to find the problem area

The following procedures are standard tests used to identify the source of abnormal brain activity.

• Baseline electroencephalogram (EEG). In this test, electrodes are placed on the scalp to measure electrical activity produced by the brain when you're not experiencing a seizure. This test can suggest general areas of the brain that may be affected.
• Video EEG. A continuous EEG with video monitoring records your seizures as they occur. Because your seizure medications have to be reduced or temporarily stopped so that seizures will occur, you'll be admitted to the hospital for this test. Evaluating the changes in your EEG with your body's movements during a seizure helps pinpoint the area of your brain in which your seizures are starting.
• Magnetic resonance imaging (MRI). This imaging test uses a magnetic field and radio waves to create detailed images that allow doctors to identify damaged cells, tumors or other abnormalities that can cause seizures.

Your surgical team may order additional tests to localize the source of seizures and to characterize the nature of the abnormal activity. These tests may include:

• Invasive EEG monitoring. If an EEG test does not show where seizures begin, monitoring may be done with surgically placed electrodes. The surgeon places either grids or strips of electrodes on the surface of the brain or places electrodes deeper inside the brain. EEG monitoring is done while you're unconscious.
• Video EEG with invasive electrodes. Surgically placed electrodes may also be needed for a video EEG procedure. After the surgery, the video and EEG data are captured during a hospital stay while you're awake but not taking anti-seizure medications.
• Positron emission tomography (PET). This specialized imaging device is used to measure brain function when you're seizure-free. The images alone — or combined with MRI data — can help identify the source of your seizures.
• Single-photon emission computerized tomography (SPECT). This procedure measures blood flow in the brain during a seizure. Typically, blood flow is higher in the part of the brain where seizures occur. You will be admitted to the hospital to undergo this test.

Evaluations to understand brain function

Depending on the surgical site, your team may recommend tests to determine the precise areas of the brain that control language, sensory functions, motor skills or other critical functions. This information helps your surgeon preserve function to the greatest extent possible when removing or altering a site in your brain.

The test may include the following:

• Functional MRI. This test identifies regions of brain activity when you're doing a particular task, such as listening or reading. This helps the surgeon know the precise locations in your brain that control a particular function.
• Wada test. With this test, an injected medication temporarily puts one side of your brain to sleep at a time. You're then administered a test for language and memory function. This test can help determine which side of your brain is dominant for your language usage. While functional MRI has often replaced this test, it may be used if the imaging study isn't possible for you.
• Brain mapping. Small electrodes are surgically placed on the surface of the brain. When you're alert after the surgery, you perform a number of tasks that are matched with measurements of your brain's electrical activity.

Neuropsychological tests

Additionally, testing is usually recommended to measure verbal and nonverbal learning skills and memory function. These tests may provide additional insight into the area of the brain affected by seizures, as well as a baseline for measuring function after surgery.