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Most epilepsy patients considering surgery undergo the Wada test.
The "Wada Test" is named after the Japanese physician who first
performed it, Dr. Juan Wada.
The Wada test looks at language and memory on one side of the brain at a
time. Language (speech) is controlled by one side of the brain (in most people,
the left side), and the Wada will tell the doctors which side controls language
in your brain. Memory can be controlled by both sides of the brain; the Wada
test tells which side of the brain has better memory. If the side that controls
language or has better memory is where your seizures may be coming from, the
surgeon may consider performing brain mapping before surgery.
Who performs the test?
Two doctors are usually involved in performing a Wada test: a
neuroradiologist (who uses imaging devices and substances to study the brain)
and an epileptologist (a neurologist who specializes in epilepsy).
What's an angiogram?
An angiogram is conducted before the Wada test. This looks at blood flow
within the brain to make sure that there are no obstacles to performing the
Wada. The neuroradiologist inserts a catheter (a long, narrow tube) into an
artery in the leg. The catheter is directed to the right or left internal
carotid artery in the neck, which supplies the brain with blood. Once the
catheter is in place, a dye is injected. Some patients report a warm sensation
when this happens. The dye can be seen on a special x-ray machine. This machine
takes pictures of the dye as it flows through the blood vessels of the brain.
Once the angiogram is done, the catheter will stay in place for the Wada test.
What happens during the Wada test?
During the Wada test, the neuroradiologist puts one side of your brain to
sleep for a few minutes. This is done by injecting Brevital (a barbiturate) into
the right or left internal carotid artery. If the right carotid is injected, the
right side of the brain goes to sleep and cannot communicate with the left side.
Once the physicians are sure that one side of your brain is asleep, the
epileptologist will show you objects and pictures. The awake side of the brain
tries to recognize and remember what it sees.
After just a few minutes, the Brevital wears off. The side that was asleep
starts to wake up. Once both sides of your brain are fully awake, the
epileptologist will ask you what was shown. If you do not remember what you saw,
items are shown one at a time, and you are asked whether you saw each one
before. Your responses will be recorded.
After a delay, the other side of your brain is put to sleep. To do this, the
catheter is withdrawn part of the way and threaded into the internal carotid
artery on the other side. A new angiogram is done for that side of the brain.
Different objects and pictures are shown, and the awake side (which was asleep
before) tries to recognize and remember what it sees. Once both sides are awake
again, you will be asked what was shown the second time. Then you are shown
items one at a time and asked whether you just saw each item.
How long does the test take?
The Wada test can vary between centers. The usual test takes between 30 and
60 minutes to complete. You will need to be NPO (i.e., have nothing by mouth)
after midnight the night before this test.
Is the Wada test safe?
A Wada test is generally a safe procedure with very few risks. There is a
small risk of some complications. These complications can be as minor as pain
where the catheter is inserted or as serious as a potential stroke. Since it is
considered an invasive procedure it does carry the risk of bleeding and
infection. The risk of stroke is less than 1% overall. It is greater, but still
relatively low, if you are older or if you have artherosclerosis (hardening of
the arteries) or a history of high cholesterol.
What's the recovery time after the procedure?
You will be on bed rest with bathroom privileges the remainder of the day in
the hospital. The nurses and doctors will be checking the pulses in the leg
where the catheter was inserted and will also check under the dressing. Sensory
checks will also be done throughout the day. This is done to ensure there has
not been a disruption in circulation to the affected leg. You will be discharged
later in the day and will be given a home going instruction sheet. You are asked
to avoid strenuous activity for at least 24 to 48 hours after the procedure.
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