The Wada test can help a physician evaluate how important each side of the brain is with respect to language and memory functions. Data from the Wada test help the epilepsy team determine the approach most likely to address seizures while preserving areas of the brain associated with speech and memory.
What You Need to Know
- The Wada test can help epilepsy doctors evaluate how important each side of the brain is with respect to language and memory functions.
- A “practice test” takes place the day before, during which someone from the testing team explains the test to the patient and rehearses similar exercises to those used during the actual test.
- During the test itself, doctors temporarily put one side of the brain to sleep (anesthetize) by injecting a drug into the carotid artery.
- First one side of the brain is tested and then the other. The speech and memory function test results from both sides are compared.
Some seizures and epilepsies are due to irregularities in the brain tissue, such as scars, tumors or other lesions that can show up on angiography as changes in the blood vessels. Some of these issues can be treated with epilepsy surgery.
For patients whose seizures are likely to require surgical treatment, this two-part test is included in the pre-surgical work-up to gauge the impact of surgery on language and memory function.
Wada Test: What Happens
The first step of the Wada test is angiography — the injection of X-ray dye through a small tube called a catheter. The X-ray machine takes pictures of the flow of the dye through the arteries.
Next, a medication is injected through the catheter to temporarily “put the brain to sleep” (anesthetize it) on one side. Language, memory and other functions are tested while that side is anesthetized.
The Wada test is an outpatient procedure, but the patient must bring someone who can drive home since anesthesia is involved. Generally, the Wada test starts in the morning and the patient is ready to go home by mid-to-late afternoon.
Wada Test Preparation
Patients may be asked to avoid certain medications including aspirin or products containing aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs) and blood thinners for up to two weeks before this procedure. Ask your doctors what to do in your case.
It is important to notify the physician before the Wada test if there are any known allergies to drugs, particularly general or local anesthetics, barbiturates or benzodiazepines. It is also important to alert the doctor to any allergies to foods or x-ray dyes that contain iodine, or allergic conditions such as eczema, asthma or hay fever.
Wada Test: The Day Before
On the day before the test, the patient meets with a neuropsychology specialist who reviews what will happen and assesses the patient’s baseline speech, cognitive and memory functions. The neuropsychologist also rehearses the types of questions that will be asked and motor tests that will take place under anesthesia.
Wear comfortable clothes and shoes for the pre-Wada testing. Get a good night’s sleep and eat a full breakfast beforehand.
The Day of the Wada Test:
Wear comfortable clothing.
Do not wear makeup.
Do not eat or drink anything past midnight.
Take morning prescription medications with as little water as possible.
Wada Test: Procedure
Part 1: Angiography
The patient lies on their back on the X-ray table, and the neuroradiologist injects a local anesthetic (numbing agent) into the skin near the . The injection may cause a slight pressure and burning. Once the area is numb, the doctor makes a small incision in the groin and inserts a small, flexible tube called a catheter through the skin and into an artery.
Then the doctor guides the catheter into the vessels to be examined. An X-ray system called fluoroscopy provides a television-like viewing of the inside of the body and helps the doctor move the catheter from one position to another in the blood vessels.
Once the catheter reaches a specific blood vessel, the patient is instructed to stay still while the X-ray dye is injected through the catheter. As this happens, the patient will notice a very warm feeling lasting about 10 to 20 seconds. At the same time, the patient will hear noise as the X-ray machine takes pictures of the dye's passage through the blood vessels.
The picture-taking process takes about 15 minutes for each blood vessel the doctor examines. The duration of the test for most patients .
Part 2: Memory, Speech and Muscle Test
Next, the neuroradiologist injects a medication into the catheter. When the drug reaches the side of the brain under study, the patient will temporarily lose all strength on the opposite side of the body. Sometimes only one side is tested; other times, one side is tested first and then the other after a short interval.
During the 10 to 15 minutes when one side of the brain is sedated, the testing team assesses the patient's speech, memory, and other functions. The patient is asked to perform tasks such as reading words and identifying objects, pictures, shapes and numbers. The team asks the patient to answer questions about what is shown and to remember it so it can be recalled or recognized at the end of the test.
The test also assesses muscle responses in the patient’s hand or arm strength periodically to determine motor function.
After strength returns, the testing team checks on how well the patient can remember what was shown during the time the brain was sedated on one side.
A sound recorder or video camera will record the patient's speech and movements for further study.
After the Wada Test
At the end of the test, the doctor will remove the catheter and compress the blood vessel for 10 to 15 minutes until clotting at the incision forms a firm seal to prevent bleeding. The patient will feel pressure as a member of the radiology team presses on this area. The small incision does not need stitches — only a small bandage.
In order to ensure full closure of the incision and to lower the risk of bleeding, the patient stays in the hospital for four to five hours. Written instructions for home care are provided before the patient leaves.
After the test, the injection site may be tender and bruised. Elevating the leg and applying ice packs may help. The patient and family should inform the nurse or physician of any discomfort or unusual developments without delay.
Although the test is proved safe, the patient’s physician will discuss possible complications before the procedure. Again, it is essential that the patient inform the doctor of any allergies or sensitivities to sleeping pills, barbiturates, local anesthesia, X-ray dye, etc. to avoid complications.
It usually takes several days for the physicians to review test results and submit a report. The physician will then discuss the results with the patient.