A rare type of stroke turned out to be a significant, but preventable health issue

Subarachnoid hemorrhage, or SAH for short, is one of the most severe types of strokes. It typically occurs when an aneyrusm, a bulge in a blood vessel, in the brain bursts and bleeds between the membranes covering the brain. It is a life-threatening situation that often starts suddenly and requires immediate hospital care. Many patients who survive SAH suffer from physical and cognitive symptoms, which decrease their functional capacity and ability to perform activities of daily life.

SAH is known to be deadly but rare. From a public health point of view, it is considered to be more of a single catastrophic event than an extensive population health issue.

A massive, Finnish-led study recently published in the medical journal JAMA Neurology changes this current way of thinking. Despite its rarity, the international collaboration study shows that subarachnoid hemorrhage seems to be one of the leading causes of death worldwide among neurological and cardiovascular diseases. The sudden stroke usually occurs in healthy, working-aged people, resulting in loss of high-quality life-years. Subarachnoid hemorrhage is therefore comparable to other health issues that are considered to be much more common.

Not just a forgotten cousin of other types of strokes

Ilari Rautalin, the leader of this research project, associate professor in experimental neurosurgery and a specializing physician at HUS Neurosurgery, emphasizes the importance of the results.

“The major public health significance of strokes has been common knowledge for a long time, but until now, SAH has been thought to be a fairly marginal cause of disease when compared to cerebral infarction and bleeding inside the brain. The newly published results show that this view on SAH should now change,” Rautalin says.

SAH differs greatly from other strokes by its onset mechanism, symptoms, diagnostics, treatment, and prevention. The researchers say that the findings solely from other types of strokes cannot be applied to SAH.

One of the most extensive international projects on the matter

This research was conducted as a uniquely extensive international project. It aimed to use all published information on the matter, and data was gathered from all the countries in the world from the previous 30 years.

“Our group consists of nearly 700 leading researchers of strokes from 74 countries. This is the first project of this extent ever,” Rautalin explains.

In addition to Rautalin, Finnish researchers in the core group included Miikka Korja, a neurosurgeon and associate professor from HUS and Jaakko Kaprio, professor of genetic epidemiology at the University of Helsinki.

The burden from severe stroke can be significantly eased

In addition to demonstrating the exceptionally high burden of SAH to public health, the article offers an extensive assessment on the 14 different risk factors for SAH and their significance. All in all, over 70 percent of the SAH-related burden appears to be attributed to the associated risk factors, most importantly high blood pressure and smoking.

Reduced smoking and more effective treatment of high blood pressure during the recent decades seems to also relate to the decreased prevalence of SAH in high-income countries. However, the findings are not as positive globally. In low-income countries, the absolute number of cases and deaths have increased linearly. A major problem is also the lack of reliable research data from several regions, such as Africa and South-East Asia.

“We have several effective and scientifically proven ways to reduce the global burden of this lethal cerebral hemorrhage. However, their implementation and allocation of limited resources pose challenges. We hope that our results help politicians make choices that are effective for public health, and invest in high-quality international research,” Rautalin says.

Link to the research article: GBD 2021 Global Subarachnoid Hemorrhage Risk Factors Collaborators: Global, Regional, and National Burden of Nontraumatic Subarachnoid Hemorrhage – The Global Burden of Disease Study 2021. JAMA Neurol. doi:10.1001/jamaneurol.2025.1522. Published online May 23, 2025

In a university hospital, research is part of the treatment: we continuously evaluate and develop care based on scientific research evidence and patient experience. At HUS, we conduct close research collaboration with the Faculty of Medicine at the University of Helsinki. We publish approximately 2,400 peer-reviewed research articles) annually, which we highlight in our newsfeed.