Hemorrhagic strokes, characterized by bleeding in the brain, are less common than strokes caused by blood clots but are usually more lethal.
About 17% of strokes are caused by the rupture of a weakened blood vessel in the brain, and fewer than half of those suffering such strokes survive beyond one month, the American Heart Assn. says.
Many of those who do survive, moreover, suffer debilitating injuries, including such problems as speech impairment and paralysis.
"This is probably one of the most critical neurological conditions that we face," said Dr. David S. Liebeskind of the UCLA Stroke Center. "It's a very serious and, unfortunately, common disorder. We deal with this on a daily basis."
Damage to the brain in a hemorrhagic stroke, also known as a cerebral hemorrhage, occurs as blood escaping into the skull cavity increases pressure on brain cells, impairing their function and eventually killing them.
The outlook for Israeli Prime Minister Ariel Sharon, who suffered a hemorrhagic stroke Wednesday, is worsened by the fact that he is overweight and has been receiving blood thinners in the aftermath of a stroke he suffered in mid-December.
Blood thinners reduce the blood's ability to clot and naturally seal off any leakage that might occur in a vessel in the brain, making a bleeding episode worse than otherwise.
Sharon's chance of surviving the stroke is probably less than 20%, estimated Dr. Philip Stieg, chairman of the department of neurological surgery at Cornell University's Weill Medical College in New York City.
"It's extremely unlikely that he is going to come out of this being a walking, talking individual," Stieg said. "We're talking about a 77-year-old guy who's morbidly obese. The prognosis for him is extremely grim."
Physicians were uncertain if Sharon's stroke Wednesday was related to the one Dec. 18. Stieg noted that about 5% to 10% of clot-induced strokes are followed by a hemorrhagic stroke, in part because the original stroke kills some brain tissue and weakens nearby blood vessels.
The weakened vessel walls are then more vulnerable to rupture due to high blood pressure and other risk factors.
The chief priority in treating a hemorrhagic stroke is to drain off the excess blood to reduce pressure and to seal off the source of bleeding. The latter can be a very difficult -- and sometimes impossible -- task, depending on where the rupture is.
The normal way to achieve the sealing-off is through conventional surgery, but UCLA and some other institutions are investigating ways to place a catheter into the brain through an artery, both to drain off excess blood and to seal the wound.
Beyond that, Liebeskind said, treatment "is really just supportive care -- making sure blood pressure is not high, making sure the patient is well hydrated and doesn't have a fever, which can worsen the outcome."