Q&A: New findings on subarachnoid hemorrhage

Non-traumatic subarachnoid hemorrhage (SAH) is the third most common stroke type after cerebral infarction and cerebral hemorrhage.

A new study presents comprehensive estimates of the global, regional, and national burden of subarachnoid hemorrhage. In 2021, it is estimated that there were 700,000 new SAH cases, almost 8 million patients with prevalent SAH, and 350,000 SAH deaths. Dr. Ilari Rautalin, IHME Collaborator, discusses this research.

Video transcript

This transcript has been lightly edited for clarity

What is subarachnoid hemorrhage, its key risk factors, and why is it important to have studied it?

Non-traumatic subarachnoid hemorrhage, or SAH as we call it, is the third most common stroke type after cerebral infarction and cerebral hemorrhage. Around 85% of the SAH are caused by the rupture of a brain aneurysm, leading to bleeding in the subarachnoid space, between the brain and the surrounding layers. While the most common symptom of SAH is a sudden severe headache, SAH is also a highly fatal disease, with one-quarter of the patients dying before reaching the hospital and an overall 30-day mortality rate of around 40%.

Additionally, many survivors experience long-term physical and neuropsychological disabilities, which significantly impairs patients’ daily functioning. Key risk factors for subarachnoid hemorrhage include smoking and high blood pressure. While there is some evidence linking air pollution, low physical activity, and adverse lipid profile to an increased risk, this evidence is less robust compared to other stroke types.

Given that many SAH patients are relatively young and in good health before the event, the loss of potential life years is significant. Despite its relatively low incidence, SAH’s high mortality and morbidity rates make it the leading cause of cardiovascular and neurological deaths and disabilities worldwide. And therefore, ongoing research into the epidemiology of SAH and the development of effective preventive strategies is critical.

What are the key findings of your research?

The key findings of our recent Global Burden of Disease study include the most comprehensive estimates of the global, regional, and national burden of subarachnoid hemorrhage. In 2021, we estimated that there were 700,000 new SAH cases, almost 8 million patients with prevalent SAH, 350,000 SAH deaths, and over 10 million SAH-related disability-adjusted life years globally.

In this graph, we can see that the age-standardized prevalence of subarachnoid hemorrhage is decreasing globally. But the prevalence of SAH is higher in women than in men. The age-standardized rates are decreasing in both sexes. By Socio-demographic Index levels, we can see that the decreases are less pronounced in low- and low-middle, but also in high-income regions. On the other hand, the mortality rates are decreasing more substantially in high-income areas.

Moreover, we observed that even 72% of the burden related to SAH could be prevented by the elimination of its risk factors – most importantly high blood pressure and smoking. And overall, these findings suggest evidence for the potential health benefits of proactive public health planning and resource allocation towards the prevention of SAH.

Similar to prevalence rates, we can also see a decreasing rate of incidence, mortality, and disability-adjusted life years globally. These are also decreasing in both men and women. However, it’s important to know that the absolute numbers of SAH cases and deaths are increasing, especially in low- and middle-income countries.

What geographical variations did your research uncover?

We found that all age-standardized burden estimates of SAH varied substantially between the 204 countries and territories worldwide. The highest prevalence and the lowest mortality rates were observed in high-income regions, while the highest incidence and mortality rates were observed in low- and middle-income countries. More specifically, the greatest burden was reported in Latin America and the Caribbean, and the lowest rates were seen in the Middle East and Africa.

However, we believe that the low reported burden in some low-income countries is likely due to underreporting and misdiagnosis, rather than a truly lower disease incidence. In terms of temporal trends, we observed that the absolute number of SAH cases and deaths increased the most in low- and low-middle-income countries, which is particularly concerning.

What can be done to reduce the burden of subarachnoid hemorrhage?

Based on our findings, SAH appears to be a largely environmental disease, which could be prevented by addressing its most important risk factors, namely smoking and high blood pressure. In addition to global efforts to decrease hypertension and smoking rates, enhancing pre-hospital management, in-hospital care, the availability of diagnostic tools, neurosurgical tertiary care, and identification of unruptured intracranial aneurysms could serve as key areas for future interventions, especially in low- and middle-income countries.

At the same time, many countries, especially those in sub-Saharan Africa, do not have any SAH-specific data sources, which emphasizes the importance of international but also interdisciplinary collaboration to generate more reliable burden estimates for these regions.