Research and guidelines

Evidence on brain aneurysms is stronger than for many neurosurgical conditions. Large cohorts describe how common aneurysms are and how often they rupture, randomized trials have compared coiling with clipping after a rupture, and European, American and UK guidelines cover both ruptured and unruptured aneurysms.

How common aneurysms are, and rupture risk

A 2011 meta-analysis of 68 studies and 94,912 people found unruptured aneurysms in 3.2% of adults without other conditions, more often in women, people with polycystic kidney disease and those with a family history1. The PHASES analysis pooled six cohorts of 8,382 people and produced a score that estimates five-year rupture risk from age, high blood pressure, previous bleeding, size, location and population2. The European Stroke Organisation's 2022 guideline on unruptured aneurysms covers monitoring and the choice between observation and treatment3.

After a rupture

A 2024 meta-analysis of population studies from 1973 to 2017 found that case fatality after subarachnoid hemorrhage fell from 47% in the 1970s to about 35% in the 1990s and has changed little since. In six studies with one-year follow-up, 45% of patients were living independently4. The European Stroke Organisation published its guideline on aneurysmal subarachnoid hemorrhage in 20265, and the American Heart Association6 and NICE in the UK7 have their own guidance.

Coiling and clipping

The International Subarachnoid Aneurysm Trial (ISAT) randomly assigned patients with ruptured aneurysms suitable for either treatment to coiling or clipping. Long-term follow-up of the UK cohort, over 10 to 18 years, reports survival, independence, rebleeding and retreatment as separate outcomes8. The 2026 European guideline recommends coiling over clipping when both are suitable for an adult in good clinical condition, and notes that newer devices can't simply inherit the trial's results5.

Flow diversion

In the PREMIER study of a flow diverter for unruptured aneurysms, 115 of 138 aneurysms with three-year imaging were completely closed, and 108 of 138 met a combined measure of closure without significant narrowing of the artery or further treatment9. A 2026 randomized trial in South Korea compared flow diversion with conventional endovascular treatment for unruptured aneurysms10.

Screening

KDIGO's 2025 guideline on polycystic kidney disease, which raises the risk of aneurysms, sets out which patients should be offered screening11.

References

1. Vlak MH, Algra A, Brandenburg R, Rinkel GJ. Prevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis. Lancet Neurol. 2011;10(7):626-636. doi:10.1016/S1474-4422(11)70109-0 PubMed ↩
2. Greving JP, Wermer MJ, Brown RD Jr, et al. Development of the PHASES score for prediction of risk of rupture of intracranial aneurysms: a pooled analysis of six prospective cohort studies. Lancet Neurol. 2014;13(1):59-66. doi:10.1016/S1474-4422(13)70263-1 PubMed ↩
3. Etminan N et al. European Stroke Journal. 2022;7: LXXXI–CVI. doi:10.1177/23969873221099736. Source ↩
4. Ziebart A, Dremel J, Hetjens S, et al. Case fatality and functional outcome after spontaneous subarachnoid haemorrhage: a systematic review and meta-analysis of time trends and regional variations in population-based studies. Eur Stroke J. 2024;9(3):555-565. doi:10.1177/23969873241232823 PubMed ↩
5. Vergouwen MDI et al. European Stroke Journal. 2026;11(5):aakag043. doi:10.1093/esj/aakag043. Source ↩
6. American Heart Association. Top Things to Know: 2023 Aneurysmal Subarachnoid Hemorrhage Guideline. 22 May 2023. Guideline doi:10.1161/STR.0000000000000436. Source ↩
7. National Institute for Health and Care Excellence. NG228. Subarachnoid haemorrhage caused by a ruptured aneurysm: diagnosis and management. 2022. Source ↩
8. Molyneux AJ et al. The durability of endovascular coiling versus neurosurgical clipping of ruptured cerebral aneurysms: 18 year follow-up of the UK cohort of ISAT. Lancet. 2015;385:691–697. doi:10.1016/S0140-6736(14)60975-2. Source ↩
9. Hanel RA et al. PREMIER study: 3-year results with a flow diverter specific occlusion classification. Journal of NeuroInterventional Surgery. 2023;15:248–254 (online 2022). doi:10.1136/neurintsurg-2021-018501. Source ↩
10. Efficacy and safety of flow diverter therapy for unruptured intracranial aneurysms compared to conventional endovascular therapy: a multicentre, randomised, open-label trial in South Korea. EClinicalMedicine. 2026. doi:10.1016/j.eclinm.2026.104135. PMID 42598553. PubMed ↩
11. KDIGO. 2025 Clinical Practice Guideline for Evaluation, Management, and Treatment of ADPKD. Kidney International. 2025;107(Suppl 2S). Chapter 6. Source ↩