A study published this week in The Lancet Neurology—which analysed 162 studies spanning seven decades—has revealed, “for the first time”, an increase in the prevalence of brain aneurysms from 2.9% to 6.6% over the past two decades. The study also identifies the groups most affected by these aneurysms: women are nearly twice as likely to be affected compared to men, as are patients with polycystic kidney disease, connective tissue disorders, or a family history of subarachnoid haemorrhage (SAH). For the first time, smoking and high blood pressure have been shown to measurably increase the risk of aneurysms as well. However, according to the researchers, the study—when considered alongside other data—suggests that very few brain aneurysms require treatment.
The prevalence of brain aneurysms and the people they affect had last been systematically determined 15 years ago, with the present study providing an updated and even more extensive worldwide analysis of this prevalence. The study analysed data from 316,131 individuals, including 11,822 with an unruptured brain aneurysm.
Its key finding was that, on examinations of healthy adults using modern vascular imaging, the prevalence has more than doubled over the last two decades—rising from 2.9% between 2002–2015 to 6.6% between 2016–2022. This translates into one in 15 healthy adults having a brain aneurysm today.
The study also identifies the groups at the highest risk of developing a brain aneurysm. The most pronounced difference is between the sexes: women are affected nearly twice as often (5.5%) as men (3%). And, in a reference population without underlying medical conditions—with a mean age of 50 years and of whom 50% were women—the study estimates a prevalence of 3.9%. Significantly higher rates are further found among people with autosomal dominant polycystic kidney disease (12.8%), individuals with a family history of SAH or aneurysm occurrence (7.9%), and those with genetic connective tissue disorders, such as Marfan syndrome or Ehlers-Danlos syndrome (10.3%).
For the first time, the researchers reiterate, it has also been possible to quantify the impact of modifiable risk factors. Active smoking is associated with a 1.4-fold increased risk of aneurysms, while high blood pressure is associated with a 1.6-fold increase. The researchers add that, in practical terms, this means that the question of targeted screening needs to be reconsidered for clearly defined high-risk groups—and smoking and blood pressure are the two key factors that affected individuals can personally influence.
Additionally, in the researchers’ view, two initial explanations for this increase in aneurysm prevalence may appear “obvious”: the improved or more frequent use of imaging techniques, and the overall trend of ageing populations. However, they continue, neither factor alone accounts for the doubling observed over the last two decades; the argument that more frequent detection via sensitive imaging techniques is the cause is undermined by the fact that, during the same period, the prevalence of both small and larger aneurysms (≥5mm) doubled—rising from 0.7% to 1.4%. The ageing factor is also ruled out due to the increase persisting even when age is statistically adjusted for—although, over the broader seven-decade span of time, the ageing of the population does make a significant contribution, according to the researchers. Finally, smoking and high blood pressure can be excluded as causes, as their prevalence across the studied population is steadily declining.
“Other as-yet-unknown influences must therefore be at play—environmental factors, for instance,” said Gabriel Rinkel (University Medical Centre Utrecht, Utrecht, Netherlands), co-supervisor of the study. “Identifying these unclear factors is one of the most pressing open questions for the coming years.”
The full significance of these figures becomes apparent when viewed in the context of an earlier study by the same group. In 2019, Rinkel, Nima Etminan (University Medical Centre Mannheim, Mannheim, Germany) and colleagues demonstrated via a JAMA Neurology paper that, globally, brain haemorrhages caused by ruptured aneurysms had declined by approximately 40% over the course of three decades. A higher number of aneurysms coupled with fewer aneurysm-related haemorrhages implies, in the researchers’ view, that the proportion of aneurysms that are unlikely to rupture is significantly higher than previously assumed. Overall, roughly one in 15 healthy individuals harbours an aneurysm, yet only about one in 1,000 of these aneurysms ruptures annually.
As also submitted by the researchers behind the present study, this annual rupture risk of approximately 0.1% stands in contrast to the risks associated with preventive aneurysm closure—whether via endovascular techniques like coiling, or microsurgical clipping procedures—where there is a likelihood of roughly 2–3% of the patient suffering a stroke or dying as a result of the procedure itself.
“Our data demonstrate that an incidentally discovered aneurysm is, on average, less dangerous today than it was 20 years ago,” commented Etminan, who was the senior author for both the 2019 JAMA Neurology paper and the study published in The Lancet Neurology earlier this week. “For the vast majority of affected individuals, the appropriate course of action is therefore not a preventive procedure, but rather a careful assessment of individual risk and reliable monitoring of risk factors through periodic imaging.”
According to the researchers, these new data shine a light on a growing group of older adults with small, usually harmless aneurysms—often discovered incidentally—whose clinical significance frequently remains unclear.
Etminan also noted that this is among the driving factors behind his centre’s attempts to establish a Center for Cerebral Aneurysms, which, he posited, is not designed as a facility for performing preventive treatments “as frequently as possible” but, rather, as a resource for individual risk assessment, counselling based on the latest scientific findings, and structured long-term monitoring—including for relatives of individuals in high-risk groups. A key focus here is the development of non-invasive treatment strategies; international studies like PROTECT-U are investigating whether the risk of rupture can be reduced through medication.
“We don’t treat aneurysms—we treat people with aneurysms,” Etminan concluded. “Our data now reveal just how many people are affected. What almost all of them need is a clear answer to the question, ‘what does this finding mean for me?’”
