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Diagnostic tests

WADA Test

What is the Wada Test? (Pronounced WAH-dah)

The Wada Test, named after Dr. Juhn Wada, is used to decide how to do seizure surgery in the safest possible way. The Wada Test shows where speech and memory are located in the brain. It is important to know if the area of your brain in which surgery will be performed is close to important speech and memory functions.

The Wada Test is done by a team of specialists, which include radiology, neuropsychology, nursing, as well as other technical support staff.

How is the test performed?

Electrodes will be placed on your scalp in order for the neurologist to read your brain waves during the Wada test.

Neuropsychologist — You will have a chance to meet the neuropsychologist to go over the procedure and answer any questions you may have.

EEG — Electrodes will be placed on your scalp in order for the neurologist to read your brain waves during the Wada test.

Angiography — After being admitted for the procedure, you will be asked to lie on your back on an x-ray table. The anesthesiologist will inject a local anesthetic into your groin area. A small incision is then made to allow passage of a small catheter through the skin and into a blood vessel in your groin. The catheter is then guided into a blood vessel in your neck (the internal carotid artery). The radiologist moves the small catheter through your blood vessels by looking at an x-ray monitor. You will ordinarily not feel the tube moving.

You may feel a warm, flushed sensation as small amounts of dye are injected. This sensation disappears within a few seconds. The dye is used to create contrast in pictures of your brain's blood vessels. It is very important to lie still while the dye is injected and x-rays are taken.

The Wada Test — After the angiography is complete, the Wada Test will begin. During the Wada Test, one side of the brain is put to sleep (anesthetized) for several minutes. This is done by injecting a drug called Sodium Amytal into the catheter leading to your carotid artery.

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 for a short period of time during the test. If the left side of the brain controls speech, then the patient will have trouble talking until the effect of the drug clears.

When 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 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.

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. You will need to lie on your back for two to six hours. Please tell the nurse if you are not able to do so.

How do I prepare for the test?

• Take your medications as usual.
• Do not eat for 6 hours prior to the procedure.
• 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;
  • if you have any allergies to foods or x-ray dyes which contain iodine;
  • if you have any allergic conditions such as eczema, asthma, or hay fever or if you have kidney problems.

• If you are scheduled as an outpatient for the test, 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.

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 percent overall. The neuroradiologist will review all of the risks with you prior to the procedure.

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