Study Questions Using Surgery on Small Aneurysms

Surgeons who operate on most small aneurysms in the brain may do patients more harm than good, according to a major study released today.

As many as 15 million Americans will develop such an aneurysm during the course of their life, and the number is expected to grow as the population ages.

Surgeons have been divided over whether treatment is necessary for such patients, but the new report should lead to the first practical guidelines for care.

A team of surgeons headquartered at the Mayo Clinic report in today’s New England Journal of Medicine that if the aneurysm--a small bulge in a blood vessel--is less than about a third of an inch in diameter and the patient has never had bleeding from a previous aneurysm, the risk of bleeding or stroke is only about one-twentieth of 1% per year. This was a much smaller risk than physicians had believed, said Mayo’s Dr. David O. Wiebers, who led the study.

In sharp contrast, the risk of complications or death from the corrective surgery itself was more than 13% in the first year, much higher than previously thought, Wiebers said.

“These results are very good news for the large number of patients who have this problem,” said Dr. John R. Marler of the National Institute of Neurological Diseases and Stroke.

Ruptured aneurysms account for only about 20% of the 3 million strokes suffered by Americans each year. But the 128,000 deaths they cause represent nearly 80% of total stroke deaths.

Until about 20 years ago, physicians thought that most aneurysms were congenital. More recently, they have concluded that aneurysm formation is a common byproduct of aging. Researchers are not certain what causes them, but they are more common in women and smoking is a strong risk factor.

Physicians often did not detect such aneurysms unless they ruptured or were large enough to cause symptoms, such as a droopy eyelid or an eyeball that turns outward.

But the growing use of sophisticated imaging techniques for the brain, usually for some other symptom, often reveals unexpected aneurysms. A majority of the patients in the new study had their aneurysms identified while physicians were looking for the causes of headaches.

“In the past, we would most often have gone in and corrected [an aneurysm] after it was discovered,” said Dr. Neil Martin of UCLA. Usually, the surgery involves putting a metal clip over the base of the aneurysm to block blood flow into it. A newer treatment involves inserting a small metal coil that triggers blood clot formation, sealing off the aneurysm.

Both operations, however, can themselves lead to subsequent strokes or damaging infections--more often than surgeons had previously believed, according to the new results.

“Certainly, for older patients and those with medical problems in whom surgery would be risky, we can now feel a lot more comfortable in recommending that they [surgeons] leave small aneurysms alone,” Martin said.

In the study, 2,621 patients were enrolled at 53 centers in the United States, Canada and Europe. The study had two main parts.

In the retrospective portion of the study, researchers collected data about the medical history of 722 aneurysm patients who had already suffered bleeding from another aneurysm and 727 who had not. None of those had surgery to correct the newly diagnosed aneurysm.

In the prospective portion, they studied the complications of surgery in patients with newly diagnosed, unruptured aneurysms.

The size of the aneurysm and the patient’s previous medical history proved most important in predicting future risk.

For patients whose aneurysms were smaller than 10 millimeters in diameter--about a third of an inch--and who had never suffered bleeding from an aneurysm, the risk of rupture was one-twentieth of 1% without any treatment. For those who had previously suffered bleeding, the risk was 11 times higher, about one-half of 1%, without treatment.

“In general, patients with small aneurysms and no history of bleeding should be very confident of leading a normal lifestyle with no risk of rupture” without surgery, Wiebers said.

For aneurysms between 10 and 25 millimeters in diameter (up to about an inch), the risk of rupture was about 1% per year. For those with still larger ones, the risk was 6% in the first year alone.

Among those undergoing surgery, the risk of complications or death was 15.7% in those who had not had previous bleeding and 13.1% in those who had. The lower risk in the latter group was attributed to the generally younger age of the patients, which made them healthier to begin with.

Wiebers cautioned that the new data should not confuse patients who have a bleeding aneurysm. “That is a neurologically urgent situation and our goal is to repair it [surgically] as quickly as possible.”

And there may be other factors that could increase the need for surgery, said Dr. Louis R. Caplan of the Beth Israel Deaconess Medical Center in Boston. Physicians should examine such factors carefully for each patient rather than relying on hard and fast rules, he said in an editorial in the same journal.

Deciding whether to operate, he added, “requires the wisdom of Solomon.”