By David Brown
Washington Post Staff Writer
Friday, December 15, 2006

The experience of other people who have suffered bleeding from arteriovenous malformations inside the brain suggests that Sen. Tim Johnson (D-S.D.), who underwent emergency surgery for that condition Wednesday night, has at least a 50-50 chance of full recovery.

The 59-year-old senator may need another operation or other procedure to completely defuse the abnormal tangle of blood vessels inside his head that he was born with. But statistics suggest that his chance of suffering another bleeding episode in the near future is less than 10 percent and that his brain function is likely to improve from now on.

"I think his prognosis for recovery is very good," said Laligam Sekhar, a neurosurgeon at Harborview Medical Center in Seattle and former chairman of neurosurgery at George Washington Medical Center, where Johnson was treated. "Any disability now is going to depend on where the malformation was and what his condition was going into surgery."

Johnson's physicians provided no details on his condition. But the senator's office said he responded to his wife's voice and held her hand, and the Capitol physician, John Eisold, said he is "appropriately responsive to both word and touch" -- suggesting that he is conscious and may be able to communicate.

Many people harbor arteriovenous malformations (AVMs) unknowingly for decades. When they bleed, 10 to 15 percent of patients die within hours, 35 percent suffer permanent disability and about 50 percent recover more or less completely. The prevalence of AVMs is not known with precision, though one estimate is that about one-half of 1 percent of people have them.

They are often described as looking like "a bag of worms." They can be different sizes and may grow over time, though most apparently arise from a defect present at birth.

As their name implies, arteriovenous malformations are abnormal growths in which arteries feed directly into veins. Blood in the arteries is under high pressure, and the veins are not built to handle the pressure. Over time, the stress can cause them to leak -- or burst.

Johnson's first reported symptom was a sudden loss of coherent speech while he was on a telephone call with reporters. That suggests he may have had a small bleed near the brain's speech center, which in 90 percent of people is on the left.

Outside its normal channels, blood is highly irritating and can cause small arteries to clamp shut and temporarily starve local areas of oxygen and nutrients. A less likely explanation is that irritation by the AVM itself caused a localized seizure. In either case, a small part of the brain could be stunned and its functions temporarily lost.

Johnson did not immediately undergo surgery, which suggests that his symptoms diminished after he went to the hospital. Details of his treatment were not released, but he almost certainly had brain scans that revealed both the bleeding and the presence of the malformation.

Later, however, he was taken to the operating room. That suggests something happened -- probably a new hemorrhage and new symptoms.

"With an AVM, you are not rushed to emergency surgery unless you either rebleed or the consequences of the hemorrhage force you to operate because the pressure inside the brain is too high," said Robert Spetzler, head of the Barrow Neurological Institute at St. Joseph's Hospital in Phoenix and a leading authority on treating the condition.

The purpose of the operation would have been to reduce the pressure by taking out the clotted blood and to stop the bleeding. Some or all of the AVM might also have been removed, though that is often hard to do.

The surgery is difficult and dangerous. If the bleeding is coming from a weakened vein "downstream" of the defect, the surgeon cannot simply tie off that area. High-pressure blood will continue to flow in and will have an even smaller route out -- raising the pressure in the malformation even higher.

"If he ligates the vein first, it just basically explodes in his face," said William O. Bank, chief of neuro-interventional radiology at Washington Hospital Center.

Instead, the surgeon must cut off the flow in the arteries feeding the malformation. There may be many; if the bleeding is extensive, they may be hard to find; and getting to them may require touching the already highly unstable defect.

"It becomes very technically difficult," Bank said.

If the bleeding can be stopped, most surgeons will leave definitive treatment of the AVM for another day, once the patient has recovered. A neuroradiologist will thread a catheter from an artery in the thigh into the brain and release a dye that will fill the AVM and outline its structure.

The radiologist can then inject a gluelike substance that shuts down blood flow in the arteries to the AVM. Alternatively, a surgeon can cut the malformation out. AVMs can also be cauterized from outside the skull by crossing beams of gamma radiation and causing pinpoint burns in the blood vessels, which then form scar tissue and close off.

An AVM has about a 10 percent chance of bleeding a second time in the six months after a first hemorrhage. After that, the risk falls to what it is before the first bleed -- about 3 to 4 percent a year.