The following diagnostic procedures determine if surgical treatment for epileptic seizures is necessary. These procedures are used to assist a physician in evaluating the cause of a patient’s seizures and locate the origin of the seizures within the brain. After a procedure, a patient remains within the Epilepsy Monitoring Unit (EMU) for observation.
When we consider surgery for seizures, it is important that we know where certain speech, thinking and memory functions are located in the brain so that surgery does not affect these functions.
The information we gather from testing helps us to decide what the best type of surgery might be, and how much brain tissue can be removed safely. The Wada test is used to help make these determinations. The test combines neuroimaging and neuropsychological testing methods.
During the test, one side of the brain is put to sleep (anesthetized) by injecting a barbiturate into the carotid artery. For example, when the drug is injected into the left carotid artery, the left side of the brain is anesthetized for several minutes. Because the left side of the brain controls movement on the right side of the body, the right side of the body will not be able to move for this period of time. Also, if the anesthetized side is the side that controls speech, the patient will not be able to speak until the effect of the drug clears.
The patient will be scheduled as an outpatient for the test, the patient must bring someone who can drive and accompany them home. The patient will not be able to drive themselves home after the procedure. Generally, the procedure will begin in the morning and the patient should be ready to return home by mid-to-late afternoon.
On the day prior to the test, the patient will be scheduled for a consultation with a neuropsychology specialist. The purpose of this visit is to review the procedure with the patient and get baseline speech, cognitive and memory information. There also will be a practice session so that the patient will know what to expect during the actual test. The patient will also usually be scheduled for neuro psych testing in the afternoon of the day before the procedure.
The patient must notify us prior to the test if they have any known allergies to drugs, particularly local anesthetics or barbiturates such as phenobarbital or Mysoline (primidone), Amytal (amobarbital), Mebaral, Nembutal, Seconal, or Tuinal. It is also important that they tell us of any allergies to foods, x-ray dyes which contain iodine, or allergic conditions such as eczema, asthma or hay fever.
Part One: Angiography
After the patient has been positioned on the back on the x-ray table, the neuroradiologist will give an injection of a local anesthetic into the groin. With the injection, the patient will feel a slight pressure and burning. A small incision is then made to allow passage of a small, flexible tube called a catheter through the skin into the artery.
The catheter will be guided painlessly into the vessels to be examined. Passage of the catheter from one position to another within the blood vessels is performed with the aid of an x-ray system, called fluoroscopy, which provides a television-like viewing of the inside of the body.
After the catheter is positioned within a specific blood vessel, x-rays are taken while x-ray dye is injected through the catheter. At this time, the patient will notice a very warm feeling lasting approximately ten to twenty seconds. At the same time the patient experiences the warm feeling, the patient will also hear noise as the x-ray machine takes pictures of the dye's passage through the blood vessels. It is very important that the patient remain motionless while the dye is injected and the x-rays are taken.
Although the length of the picture-taking process can be as brief as fifteen minutes, the actual time it takes will depend on the number of blood vessels that need to be examined. Most patients can anticipate lying on the x-ray table for one to two hours.
Part Two: The Wada Test
Next, the neuroradiologist will inject sodium amobarbital into the catheter. When the drug reaches the side of the brain under study, the patient will lose all strength on the side of the body opposite to the injection. This weakness is temporary, typically lasting five to fifteen minutes. It is during these few moments that the critical assessments of the patient's speech and memory will be made.
To test the patient's speech, the patient will be asked to read words, identify objects, pictures, shapes and numbers and answer questions about what they are shown. The patient also will be asked to remember what is shown. Later in the test, the patient will be asked to recognize these items again. The patient's hand or arm strength will be checked periodically to determine the full return of motor function of the weak side of the patient's body. The patient's speech and movements will be recorded using a tape recorder and/or a video camera for further study. Sometimes only one side is tested, at other times, one side will be tested first and then, after a short interval, the other side will be tested.
At the end of the test, the catheter will be removed. The blood vessel from which the catheter is removed must be compressed for ten to fifteen minutes until clotting at the entry site forms a firm seal to prevent leakage. The patient will feel the pressure as a member of the radiology team presses on this area. A small bandage will be placed on the site; no stitches are required.
The patient will stay in the Neuroradiology Department four to five hours after which the patient will be able to go home accompanied by a companion. As mentioned earlier, the patient will not be able to drive home alone. The patient may want to bring a book or a radio with earphones to help pass the time. Written instructions for home care will be given to the patient before leaving the hospital.
The patient and family should inform the nurse or physician of any discomfort or unusual developments without delay.
After the test, the injection site may be tender and bruised. Ice packs may be applied and the leg elevated with a pillow to ease discomfort.
Although the test has proven safe, the patient's physician will discuss possible complications prior to the procedure. Again, if the patient has allergies or is sensitive to drugs such as sleeping pills, barbiturates, local anesthesia, x-ray dye, etc., the patient must inform nurses and doctors beforehand, so that they can be prepared to avoid complications.
It usually takes several days for the physicians to review test results and submit a report. The patient's physician will discuss the results with the patient.
For pre wada testing: Get a good night’s sleep, eat a good breakfast and wear comfortable clothing and shoes.
For day of the Wada: Do not eat or drink anything past midnight, wear comfortable clothing, wear no makeup and take AM meds with a little water as possible. Please do not take aspirin or aspirin containing products for 2 weeks before this procedure.
- Depth Electrodes: Depth electrodes are small, multi-contact probes that are inserted into specified areas of the brain via small holes made in the skull and covering of the brain. The insertion is guided using magnetic resonance imaging techniques (MRI), targeting a specific area within the brain during surgery. The entry point, trajectory and depth may be calculated by a computer to allow for precise placement of the electrode.
It is important to remember that the implanted electrodes are used as a test, not a treatment. Sometimes, testing with these electrodes will not find an area that can be treated surgically, or will show that surgical removal might not be safe.
- Subdural Grids: Subdural grids are sheets or strips of electrodes embedded in a thin, flexible sheet of polyurethane. Within the grid are electrode discs made of a platinum alloy. The grids are surgically placed, by way of an open craniotomy (the skull is opened to expose part of the brain), over and around areas suspected to be linked to a patient’s seizures. The exact number of discs used and specific location of placement depends on the individual needs of the patient.
- Subdural Strips: Subdural strips are generally used to determine which hemisphere of the brain, or what part of a hemisphere is the region of seizure onset. They are also used when access to a particular area of the brain may be somewhat limited.
When used alone, these strips are implanted through small burr holes in the skull about the size of a nickel. After the holes are drilled, the strips are placed under fluoroscopic guidance.
After the strips have been placed, the patient is observed for seizure activity in the EMU. The patient may also undergo cortical stimulation or functional brain mapping several times. This procedure helps the physician define the relationship between the area causing the seizures and the functional areas of the brain that need to be preserved.
This information is used to define and plan the second surgery -- removal of the strips and potentially removal of the area causing the seizures (the epileptogenic zone). The mapping is done by applying a small amount of electrical current through a pair of electrodes to see what function, if any, is directly under that electrode.
- Angiography / Wada Test: This two-part test is part of the pre-surgical work-up. It is performed in order to predict the potential impact of surgery on language and memory function. This information is used by your doctor to determine the best type of surgery for you and how much brain tissue can be safely removed to preserve areas of the brain associated with speech, memory, and thinking functions.
Request an appointment
For more information, request an appointment at the Johns Hopkins Epilepsy Center.