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CMU studies on aneurysms find many surgeries unnecessary

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Monday, June 16, 2008

A high number of patients with aortic aneurysms are getting unnecessary surgeries to repair them, according to a Carnegie Mellon University professor who is developing a better way to predict when an aneurysm is more likely to rupture.

"Just because the aneurysm is large it doesn't mean there is a risk of rupture," said Ender Finol, head of the Vascular Biomechanics and Biofluids Laboratory at CMU's Institute for Complex Engineered Systems. "I believe there is a high percentage of people that are being operated that don't need the surgery."

An aortic aneurysm is an abnormal bulge in the wall of the aorta, the body's largest and most important artery, which carries oxygen-rich blood.

The aneurysms tend to have no symptoms and are typically discovered by chance during X-rays. If they rupture, they can cause life-threatening internal bleeding. About 15,000 people die every year from aortic aneurysms, according to federal statistics.

Last year, vascular surgeons in Pennsylvania performed nearly 1,500 surgeries to repair aortic aneurysms in the abdomen, the section of the body where most of them tend to occur.

In Western Pennsylvania, the leading hospitals doing the surgeries were UPMC Presbyterian in Oakland, with 136 cases in 2006, and Allegheny General Hospital in the North Side, with 110 cases, according to the Pennsylvania Health Care Cost Containment Council.

To date, the best way to predict a rupture is by monitoring the aneurysm as it gets larger in diameter, said Dr. Satish Muluk, director of vascular surgery at Allegheny General. When it widens to 5 centimeters, doctors agree surgery is needed because that's the threshold when the artery is likely to rupture.

But Muluk believes size should not be the only parameter to determine whether it will rupture.

"There are cases in which a smaller aneurysm may rupture and a larger aneurysm may not rupture," Muluk said.

The technique under development at CMU intends to assess the risk by using factors other than size, including the shape and thickness of the arterial wall, Finol said.

Using images obtained through MRI or CT scans, researchers are creating three-dimensional models of the aneurysm. The images are run through computer software that, based on a set of assumptions such as blood pressure, can predict the distribution of the stress on the wall.

Measuring how much stress the wall can take -- akin to how much a piece of fabric can be pulled until it tears -- can better predict when it will rupture, Finol said.

Finol has received a two-year, $602,000 grant from the National Institutes of Health for the project. He expects to enroll about 50 patients from Allegheny General to test the technique.

Improved methods of prediction could benefit patients who often endure surgeries. Aneurysms can affect anyone, but are most often seen in men ages 40 to 70.

"Sometimes you have to (weigh) the risk of having a surgery of this kind against the life expectancy of the patient," Finol said.

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