CHICAGO -- A brain aneurysm is a weak bulging spot on the wall of a brain artery affecting 3 to 5 percent of Americans, according to the Brain Aneurysm Foundation.

Aneurysms form silently from wear and tear on the arteries, and sometimes can form from injury, infection, or inherited tendency. Bursting brain aneurysm is a silent killer that often strikes without warning.

An ongoing study at Northwestern Memorial Hospital in Chicago is identifying which patients should be screened for brain aneurysms that could burst. The study involves people who have family histories of the disease.

At 60 years old, Chicago-area resident Marsha Stark was just a few years younger than her mother was when she died of a massive brain hemorrhage.

"I knew I was a bit of a walking time bomb," Stark said.

Then last year, an aneurysm bled into her sister's brain.

"It will be a year next month, and it's a long way," Stark said of her sister. "She'll never be able to go home and live on her own."

Stark's doctor warned her that some brain aneurysms might run in the family. As with most cases, Stark had no symptoms, but her doctor recommended she be screened anyway.

Dr. Hunt Batjer, of Northwestern Memorial Hospital, found three blood vessels that could someday burst in Stark's brain.

"Looking at the artery right behind her left eye ... you can see (an) overweight mass ... which is a middle-swivel artery aneurism," Batjer said. "If an event happens, it carries a 50 to 80 percent mortality, so it's a very high-stakes game."

Stark recalled finding out about her diagnosis.

"He came to the table and put his hand on my shoulder and -- very sympathetic -- said, 'You have three,'" Stark said. "And so it was the devastation of, 'I'm in the same boat as my sister.'"

But unlike her sister, Stark was able to have her aneurysms fixed before they burst. The surgery created some muscle weakness in her eye and jaw, but those side effects are only temporary, doctors said.

Stark now focuses on the early warning she received that the condition might be hereditary.

"Because of my sister's problem, she saved my life," Stark said.

The research at Northwestern Memorial Hospital is part of an international study on heredity and aneurysms.

Additional Resources:

• Brain Aneurysm Foundation
• National Institute of Neurological Disorders and Stroke