Brain aneurysms are more common than most people expect. Roughly 2% to 3% of adults are living with an unruptured aneurysm right now, most without knowing it. That translates to millions of people walking around with a small bulge in a brain artery that may never cause a single symptom.
Prevalence in the General Population
Large systematic reviews combining autopsy and imaging studies put the prevalence at about 2.3% for adults without specific risk factors, with the rate climbing as people age. Because aneurysms are rare in people under 20 and far more common after 50, the overall figure depends heavily on the age group being studied. Estimates in published research range from 2 to 90 per 1,000 people, but the most widely accepted number for healthy adults lands near 2% to 3%.
Improved imaging technology is also revealing more aneurysms than ever before. A large hospital review of over 288,000 brain scans found that detection rates for unruptured aneurysms rose from 1.7% in 2005 to 2009, to 2.5% in 2010 to 2014, and 3.4% in 2015 to 2019. That increase was especially steep in people over 70. This doesn’t necessarily mean aneurysms are becoming more common. It likely reflects the fact that more people are getting high-resolution brain scans for headaches, dizziness, or other unrelated complaints, and small aneurysms are being spotted incidentally.
Who Gets Them Most Often
Women are significantly more likely than men to have a brain aneurysm. About 65% of all patients with unruptured aneurysms or aneurysm-related bleeding are women, and women face roughly 40% higher odds of rupture compared to men even after adjusting for other factors. Women diagnosed with aneurysms also tend to be slightly older, averaging around 62 years compared to about 60 for men.
Age is a major factor on its own. Prevalence tends to increase steadily from middle age onward, with detection rates climbing fastest in people in their 60s, 70s, and beyond.
Risk Factors That Raise the Odds
Smoking is one of the strongest modifiable risk factors. Women ages 30 to 60 who smoke have roughly four times the risk of developing a brain aneurysm compared to nonsmokers. When smoking is combined with high blood pressure, the risk jumps to about seven times that of a nonsmoker with normal blood pressure. High blood pressure on its own also raises risk, as does heavy alcohol use and stimulant drug use, all of which put extra stress on artery walls.
Family history matters, too. While about 1% to 3% of the general population has an aneurysm, that figure can reach as high as 30% in certain families with a strong hereditary pattern. If you have two or more first-degree relatives (a parent, sibling, or child) who have had a brain aneurysm, screening with a brain MRI is generally recommended. Connective tissue disorders and a family history of aortic aneurysms also increase risk.
Most Aneurysms Never Rupture
The fear surrounding brain aneurysms centers on rupture, which causes a type of bleeding called subarachnoid hemorrhage. But the actual annual rupture rate for most unruptured aneurysms is very low. Small aneurysms under 7 millimeters in patients with no prior bleeding history rupture at a rate of about 0.1% per year. Even looking across all small aneurysms (under 10 millimeters) managed without surgery, only about 1.1% ruptured over an average follow-up of nearly four years.
Size is the single biggest predictor. Aneurysms 3 millimeters or smaller ruptured at about 0.8% over the study period, those 5 millimeters or smaller at about 1.0%, and larger aneurysms carried progressively higher risk. Location also matters: aneurysms on certain connecting arteries toward the front and back of the brain carry higher rupture risk than those in other spots. Irregular shape, sometimes described as having a small blister or outpouching on the aneurysm wall, is another warning sign that doctors watch closely.
What Happens When One Does Rupture
When rupture occurs, the consequences are serious. Between 22% and 26% of people die before reaching the hospital. Among those who make it to the emergency department, another 19% to 20% die during hospitalization. Altogether, roughly 36% to 42% of patients who survive report poor long-term outcomes, including lasting cognitive problems, fatigue, or physical disability.
The outlook is not uniformly grim, though. Among patients who survive the first week, the five-year mortality rate drops to about 8%. And recovery can continue for years. In one large study tracking survivors out to five years, more than half reported no measurable disability at all, and another 23% had only minor symptoms. Most of the functional improvement happened in the first four years, then leveled off.
How Unruptured Aneurysms Are Managed
When a small aneurysm is found incidentally on a brain scan, the most common approach is observation rather than immediate intervention. For aneurysms under 7 millimeters with a regular shape and a favorable location, periodic imaging (typically a follow-up scan every 6 to 12 months at first, then less frequently) is standard. The goal is to watch for growth or shape changes that would signal increasing risk.
Treatment becomes a stronger consideration when an aneurysm is larger, irregularly shaped, located in a higher-risk area, or found in someone with a family history of rupture. The two main options are a minimally invasive catheter-based procedure that fills the aneurysm from the inside, or open surgery to place a clip across its base. Both carry their own risks, so the decision involves weighing the small but real chance of rupture against the potential complications of the procedure itself. For many people with small, stable aneurysms, the math favors careful monitoring combined with aggressive blood pressure control and quitting smoking.