This article originally appeared in the February 2004 Harvard Health Letter and is provided courtesy of Harvard Health Publications.

Brain aneurysms

Advances in imaging technology mean they’re easier to detect. The hard part is deciding when to look for a brain aneurysm — and when and how to treat it.
At the base of your brain, below where all the real thinking occurs, is a busy hub of arteries called the circle of Willis. The blood vessels that form and branch off from this rotary are the trunk lines of the elaborate network of arteries that keep the blood-hungry brain amply fed. Sometimes, this network is taxed beyond its limit. A weak spot, usually at the junction of two arteries, balloons out under pressure from the blood coursing inside, and an aneurysm forms. If one of these intracranial (inside the head) aneurysms breaks open, blood floods into a narrow area between the surface of the brain and the skull, called the subarachnoid space. This subarachnoid bleed, or hemorrhage, can be devastating. Almost half of those who have one die, and a third of the survivors have a major neurological problem.

The different types of hemorrhagic stroke
Subarachnoid hemorrhages are just one type of hemorrhagic, or bleeding, stroke. Intracerebral hemorrhages occur from smaller blood vessels deeper inside the brain and are more directly related to high blood pressure. Lobar hemorrhages occur in the parts of the brain that control speech, vision, and so on.

Looking for aneurysms
Already many unruptured aneurysms are being found when brain scans are ordered for other reasons. Brain imaging has improved remarkably. A CT scan that might have taken hours 10 years ago can now be done in minutes. The resulting pictures are amazingly detailed; they show aneurysms just a few millimeters in size. MRIs have also gotten much sharper.

So it’s conceivable that doctors might order brain scans routinely. Some studies have shown that this sort of screening may be cost effective for aneurysms that affect the aorta, the massive artery in the abdomen that comes directly out of the heart. And relatives of people who have had aortic aneurysms are frequently getting their aortas looked at.

But most experts think that routine screening of the general population for intracranial aneurysms would be hugely wasteful and counterproductive. From autopsies and other studies, experts estimate that 10–15 million Americans (about 5% of the population) are walking around with intracranial aneurysms that are producing no symptoms. Each year, about 27,000 of those aneurysms rupture and cause subarachnoid hemorrhages. So a screening program in the general population might detect one or two aneurysms before they have a chance to rupture for every five hundred or so that aren’t causing a problem and probably never will. Moreover, it’s often difficult to tell just by looking at the results of a scan whether an aneurysm is likely to break open. The size and location offer some important clues, but in many cases there’s no simple way of telling.

There’s also the danger of the treatment to consider, and whether it might outweigh that of leaving the unruptured aneurysm alone and running the risk that it will break open. It’s difficult to assign a mortality rate to the current treatments, but some studies show that it’s in the neighborhood of 2%–4%. Even in successful cases, the recovery often takes months and may involve headaches, depression, and memory loss.

Who should get a brain scan?
A more fruitful approach might be to narrow down the group of people to be screened. Studies have identified some risk factors for a ruptured aneurysm, including cigarette smoking, alcohol consumption, menopause in women, and possibly hypertension, but they’re not pronounced enough to be strongly predictive.

Subarachnoid hemorrhages run in families, which suggests a genetic cause, but there’s no genetic test yet. So right now, family history is the best guide. If any of your parents, siblings, or children has had a subarachnoid hemorrhage, you should talk to a doctor about the pros and cons of getting a brain scan. Some studies argue for scanning those with at least two affected relatives, but others have found the benefit to be questionable even in that group.

A rare inherited condition called autosomal dominant polycystic kidney disease is another reason to get a brain scan for an aneurysm. About 4% of young adults with this condition have aneurysms, and the proportion increases to 10% as they get older. Ruptures in people with this disease occur most often before age 50 and in those with high blood pressure that hasn’t been controlled.

What if a CT scan or MRI has found an unruptured aneurysm in one close relative? What if one relative has had a subarachnoid hemorrhage and an unruptured aneurysm was detected in another? Should you get a CT scan then? Researchers have yet to analyze all these scenarios, and they may never have firm answers for all of them. For now and the foreseeable future, the decision is yours and your doctor’s. Because the consequences of a ruptured aneurysm are so serious, some people will want to know if they have an aneurysm and then whether it should be treated. Others may decide against a scan after looking at the relatively low chance of rupture and the risks of treatment.

Should it be treated?
Once an intracranial aneurysm is found, doctors and patients must answer two major questions. Should it be treated? And if so, how? Both questions defy easy answers.

Whether treatment is a good idea depends on a host of factors: the person’s age, overall health, and whether the aneurysm is causing any neurological problems, among many other things. Naturally, one of the prime considerations is the chance that the aneurysm will rupture. As might be expected, most studies show that the smaller the aneurysm, the lower the risk. Results from the International Study of Unruptured Intracranial Aneurysms (ISUIA), published in the July 12, 2003, Lancet, show an annual rupture rate of about 1 in 1,000 among patients with untreated aneurysms less than seven millimeters in diameter who haven’t had a previous subarachnoid hemorrhage. None of the present treatments is going to improve on that number, so forgoing treatment is the safer bet. The location of the aneurysm must also be factored in. As a rule, aneurysms affecting the arteries that supply the posterior (back) part of the brain are more likely to burst and therefore better candidates for intervention. In the ISUIA study, half of the large aneurysms (25 millimeters or larger) in the posterior arteries ruptured over a five-year period. Fortunately, though, about 90% of intracranial aneurysms are in the anterior circulation and are far less likely to rupture.

Some aneurysms cause symptoms such as headaches and neurological problems even if they haven’t ruptured. They’re more likely to be treated, although it isn’t automatic, particularly in an older person. Any remaining aneurysms after a subarachnoid hemorrhage are also strong candidates for treatment.

How should it be treated?
Doctors treat brain aneurysms in two basic ways. The traditional approach, developed over 60 years ago, is to put a clip around the “neck” of the aneurysm, where it bulges off from the artery, which steers blood flow away from the weakened walls of the aneurysm so that it won’t break open. The clips are tiny, but it’s still a major operation that involves general anesthesia and cutting open the skull. Although these aneurysms affect arteries at the base of the brain, the procedure is usually done through a hole in the upper part of the side of the head.

The other treatment, developed about 10 years ago, involves coiling a thin strand of wire inside the aneurysm. Blood clots in and around the coil instead of pushing on the weak walls of the aneurysm. This is an endovascular procedure, meaning that it’s performed from within the vascular system. Doctors snake the slenderest of catheters through blood vessels all the way from the groin to the head, find the aneurysm, and release the wire into it. Coil treatment doesn’t require general anesthesia, and it has been heralded as less invasive than the older way of treating brain aneurysms.

So which is better, clipping or coiling? Two years ago a study of ruptured aneurysms concluded that coiling resulted in fewer deaths and serious neurological problems. That study had flaws, however, and the results don’t apply to unruptured aneurysms. The ISUIA study of unruptured aneurysms mentioned earlier also compared clipping and coiling. A year after the procedure, 9.8% of patients treated with the coils had died or become sick, compared with 12.6% of those who had clips inserted. Older patients, in particular, fared better with coils. But even if the short-term risks of clipping are greater, many doctors believe it’s more effective over the long term because it does a better job of sealing off the aneurysm.