Background

      Most patients considering surgery for epilepsy will undergo a Wada (pronounced WAH-dah) test prior to surgery. The test is named after Dr. Juhn Wada, who developed it to identify which side of the brain contains speech, and to assess how memory is shared between the two sides of the brain. This information is needed to decide how to carry out brain surgery in the safest possible way, when the surgical area may be close to important speech and memory functions. The Wada Test is conducted by a team made up of specialists in radiology, neuropsychology, nursing, and other technical support staff.

Alternative Names

      Intracarotid Amobarbital Procedure (IAP)

How the test is performed

  Angiography

     You will be positioned lying on your back on an x-ray table. The neuroradiologist will inject a local anesthetic into the groin area. A small incision is then made to allow passage of a small catheter through the skin and into the artery. The catheter is then guided into the vessels to be examined. An X-ray machine will be placed over your upper body and while observing the screen, the radiologist will move the tube through your blood vessels until it reaches your neck. You will ordinarily not feel the tube moving, though you may feel a warm, flushed sensation as small amounts of dye are injected. This sensation disappears within a few seconds. When the tube is in position, pictures of your brain’s blood vessels will be taken. It is very important to lie still while the dye is injected and x-rays are taken. When the Wada test is complete, the catheter will be removed. The blood vessel from which the catheter was removed must be compressed until clotting at the entry site forms a firm seal to prevent leakage. Depending on your own anatomy, you will need to continue lying on your back from two to six hours. The neuroradiologist will determine this following the procedure.

  The Wada Test

     Once the angiography is complete, the Wada test will begin. During the test, one side of the brain is put to sleep (anesthetized) for several minutes by injecting a barbiturate into the internal carotid artery through the catheter. When the left carotid artery is injected, the left side of the brain goes to sleep. 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 during for a short period of time. If the left side of the brain controls speech, then the patient will having trouble talking until the effect of the drug clears. Once the doctor is sure that the drug is working and that one side of the brain is asleep, the neuropsychologist will show you some objects and pictures to see if the awake side of the brain can recognize and remember what it sees.

     After a few minutes the effect of the drug wears off. Once both sides of the brain are fully awake, the neuropsychologist will ask if you to recognize the items that you were shown.

     After a short break, the other side of the brain will be put to sleep and the procedure will be repeated. The catheter is withdrawn part of the way and threaded into the internal carotid artery on the other side. A new angiogram is then performed for that side of the brain. The neuropsychologist will present new objects and pictures, and the awake side (previously asleep) will try to identify and remember what is shown. Again, when both sides of the brain are fully awake, you will be tested to see what new objects you recognize.

How to prepare for the test

     If you are scheduled as an outpatient for the test, you must arrange for someone to drive and accompany you home. You will not be able to drive home after the procedure. Generally, the procedure is scheduled in the morning and you should be ready to return home by mid to late afternoon.

     You will be asked to fast for 6 hours prior to the procedure. Take your medications as usual.

     You must notify us prior to the test if you have any known allergies to drugs, particularly local anesthetics or barbiturates such as Phenobarbital or Mysoline (primidone), Amytal (amobarbital), Meberal, Nembutal, Seconal, or Tuinal. It is also important for us to know if you have any allergies to foods or x-ray dyes which contain iodine, or any allergic conditions such as eczema, asthma, or hay fever.

What are the risks

      The Wada test generally has a small risk of complications. Minor complications include pain where the catheter was inserted, rash, and headache. A more serious complication is stroke, but the risk is less than 1% overall. The neuroradiologist will review all of the risks with you prior to the procedure.