300,000 in the USA afflicted by ailment; most don't know it

By Steve Sternberg, USA TODAY -
Sen. Tim Johnson is one of about 300,000
people in the USA with the congenital defect called arteriovenous
malformation (AVM). Most people don't realize they've got the problem
until they suffer a seizure or an episode of internal bleeding.

Here is a guide to AVMs from University of
Pennsylvania neurosurgeon Sean Grady and the National Institute of
Neurological Diseases and Stroke:

Q: What are AVMs?

A: They're tangles of abnormal arteries and
veins in the brain that are believed to occur before birth. Large
arteries that usually supply blood to webs of smaller vessels that
nourish the brain instead bypass those vessels and connect directly to
veins, which carry blood out of the brain.

Q: Why are they harmful?

A: Veins can't handle as much pressure as
arteries, which are built to contain blood pumped out by the heart.
Veins are more prone to rupture, causing bleeding. AVMs also can cause
seizures because they deprive brain tissue of blood. Only about 12% of
those with AVMs, about 36,000 people, suffer from these symptoms each
year.

Q: How do you know when you have an AVM?

A: Either you'll develop a seizure and lose consciousness or suffer a brain hemorrhage, like Johnson's.

"People describe it as being struck by lightning," Grady says. "It's unmistakable."

Q: How can they go undetected for so long?

A: The arteries that go into an AVM bypass brain
tissue, so an AVM often has no effect on the brain until a hemorrhage
occurs. When blood collects inside the closed box of the skull it can
boost pressure on the brain and cause brain damage.

Seizures occur when an AVM "steals" the blood
supply of a portion of the brain by hooking directly to veins, which
carry blood to the heart. Over time, oxygen deprivation may cause a
seizure.

Q: How dangerous are they?

A: Seizures and hemorrhages can severely damage
brain tissue. Surgery to repair the AVM can be dangerous too,
especially if it is buried in critical structures of the brain. Surface
repairs are safer and easier.

Q: How do doctors treat AVMs?

A: First, they perform a CT scan, which is the
best way to detect blood in the brain. Usually, doctors can make a
treatment decision based on a CT scan alone. If the test is positive,
the patient is taken directly to surgery.

Doctors don't remove the AVM. That comes later.
First they'll remove the clot and stabilize the patient. Once the
patient recovers, doctors will operate again to remove the AVM. First
they inject a kind of glue to choke off its blood supply; then they
surgically remove it or destroy it with high energy radiation from a
gamma knife. About 5,000 patients are treated every year. The prognosis
varies from patient to patient.

Q: What happens if you don't treat AVMs that cause bleeding?

A: The blood vessels are so weakened that they may burst again, at a rate of about 3% a year.