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Unruptured intracranial aneurysms: development, rupture and preventive management

  • Review Article
  • Published:

From Nature Reviews Neurology

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An Erratum to this article was published on 01 February 2017

This article has been updated

Key Points

  • Up to 3% of the general population carries an unruptured intracranial aneurysm (UIA)

  • Uncritical preventive aneurysm repair carries disproportionate risks of complications, whereas uncritical conservative management with or without follow-up imaging leaves patients at a small but definite risk of aneurysm rupture

  • The decision of how best to manage patients with UIAs is based on several factors, including patient age, risk of rupture and treatment, and level of anxiety related to diagnosis

  • A better understanding is required of the magnitude of risk of rupture associated with factors such as smoking and aneurysm morphology

  • More-robust data are needed on the risks and efficacy of endovascular versus surgical preventive aneurysm repair

  • Future studies should address the role of risk factor modification, including smoking cessation and treatment of hypertension, as well as anti-inflammatory drugs as treatments for unruptured aneurysms that do not require preventive repair

Abstract

Saccular unruptured intracranial aneurysms (UIAs) have a prevalence of 3% in the adult population, and are being increasingly detected because of improved quality and higher frequency of cranial imaging. Large amounts of data, providing varying levels of evidence, have been published on aneurysm development, progression and rupture, but less information is available on the risks and efficacy of preventive treatment. When deciding how to best manage UIAs, clinicians must consider the age and life expectancy of the patient, the estimated risk of rupture, the risk of complications attributed to preventive treatment, and the level of anxiety caused by the awareness of having an aneurysm. This Review highlights the latest human data on the formation, progression and rupture of intracranial aneurysms, as well as risks associated with preventive treatment. Considering these we discuss the implication for clinical management. Furthermore, we highlight pivotal questions arising from current data on intracranial aneurysms and the implications the data have for future experimental or clinical research. We also discuss data on novel radiological surrogates for rupture for those aneurysms that do not require preventive occlusion. Finally, we provide guidance for clinicians who are confronted with patients with incidentally detected UIAs.

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Figure 1: Proposed scenarios for aneurysm formation, progression and rupture.
Figure 2: Risk of aneurysm growth over time.
Figure 3: Cumulative risk of rupture associated with different risk factors.

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Change history

  • 01 February 2017

    In the initially published version of this article, the colour coding of the graphs in panels d and e of Figure 3 was incorrect. This error has been corrected in the HTML and PDF versions of the article.

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Acknowledgements

N.E. and G.J.R would like to thank S. Gingerich for the artwork used in Boxes 1 and 2 and Fig. 1, and J. Greving for creating Fig. 2 on the basis of data from the PHASES study.

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N.E. and G.J.R. wrote the article. Both authors contributed equally to the preparation of the manuscript, and drafted the figures with S. Gingerich and J. Greving.

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Correspondence to Nima Etminan.

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The authors declare no competing financial interests.

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Glossary

Non-saccular aneurysms

Aneurysms that are fusiform in shape and involve the parent vessel wall circumferentially.

Saccular aneurysms

Aneurysms that bulge out at a cerebral artery bifurcation and contain a distinct neck where they attach to the parent vessel(s).

Haemodynamic stress

Stress that is placed on the vessel wall by the flow of blood and its corpuscular components.

Hypertension

In the context of this Review, hypertension, whether treated or untreated, is defined as a positive risk factor when the systolic blood pressure is >140 mmHg.

Smoking

In the context of this Review, smoking is defined as a positive risk factor for unruptured intracranial aneurysm rupture if adults have smoked 100 cigarettes in their lifetime or smoke cigarettes (either daily or non-daily) at the time of clinical presentation.

Tunica adventitia

The outermost tunica layer of a blood vessel surrounding the tunica media. The tunica adventitia predominantly contains collagen type I and embeds a vessel into surrounding tissue. Cerebral arteries do not display a meaningful tunica adventitia, which is often discussed as a structural prerequisite for intracranial aneurysm formation.

Myointimal hyperplasia

Translocation and proliferation of vascular smooth muscle cells in response to endothelial injury with thickening of the luminal aspect of the vessel wall.

Aspect ratio

Aneurysm height divided by neck width. An aspect ratio greater than 1.6 is reported to be associated with increased rupture risk.

Size ratio

The largest aneurysm diameter divided by parent artery diameter. When larger than 3, the size ratio is reported to be associated with rupture risk.

Neck remnants

Residual filling of the neck, or part of the neck, of an aneurysm. Aneurysms that are incompletely treated can radiologically display a neck remnant, which may need observation and subsequent treatment if the remnant is enlarged.

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Etminan, N., Rinkel, G. Unruptured intracranial aneurysms: development, rupture and preventive management. Nat Rev Neurol 12, 699–713 (2016). https://doi.org/10.1038/nrneurol.2016.150

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