• prevalence of unruptured (asymptomatic) intracranial aneurysms (UIA) ~ 0.5-5%
    • modern and widely used imaging methods increase the rate of incidentally detected intracranial aneurysms
    • multiple aneurysms are found in 20-30% of cases
  • management of unruptured aneurysms is controversial
  • in the process of decision-making, weigh the individual risks of conservative management and intervention, consider several prognostic factors
  •  distinguish:
    • incidental aneurysm + personal history of SAH from another aneurysm – the highest risk of bleeding (up to 10 times higher compared to true incident aneurysm)
    • incidental aneurysm + positive family history of SAH
    • incidental aneurysm + negative family and personal history of SAH

Risk factors

Risk factors for aneurysm formation
Congenital Acquired
AD polycystic kidney disease
Fibromuscular dysplasia (MD)
hereditary hemorrhagic telangiectasia
neurofibromatosis type 1
tuberous sclerosis
coarctation of the aorta
Ehler-Danlos type IV
Marfan syndrome
α1-antitrypsin deficiency
age > 50 years
alcohol abuse
cocaine or amphetamine abuse
head trauma

Prognostic factors

Aneurysm characteristics

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Patient characteristics

  • age, gender, and comorbidities (⇒ higher surgical risk)
    • according to ISUIA, mortality/morbidity for age < 45 years was 6.5%,  45-65 years  14.4%, and > 65 years 32%
    • ↑ risk of rupture in decompensated hypertension
    • ↑ risk for smokers (up to 4-fold in women)  [Ogilvy, 2020]
    • ↑ risk in women
  • race
  • history of SAH due to another aneurysm (~10-fold risk)
  • family history of SAH (highest risk with ≥ 2 affected relatives)

Experience of a surgeon/interventional radiologist

  • combined morbidity/mortality

Prognostic scores

UIA score

The unruptured intracranial aneurysm treatment score [Etminan, 2015]

→ UIA score calculator

The unruptured intracranial aneurysm treatment score
PHASES score
PHASES score – prediction of the risk of aneurysm rupture  [Greving, 2013]
< 70 y
≥ 70 y
Aneurysm size
< 7 mm
7-9.9 mm
10-19.9 mm
> 20 mm
Previous SAH
Aneurysm location
ACA, PCA, PComA, and posterior circulation
PHASES risk score
PHASES - risk of rupture / 5 yrs


  • patients should be informed about the risks and benefits of conservative treatment, clipping, and coiling (AHA/ASA 2009 IIa/B)
  • procedure risks:
    • post-craniotomy epilepsy
    • periprocedural stroke
    • aneurysm rupture
  • balance the rupture risk per year versus patient life expectancy
  • a randomized trial comparing surgical and conservative management of unruptured aneurysms is not available and cannot be expected soon
  • there is a paradox between the fact that, according to ISUIA, the risk of bleeding is low in small aneurysms (<7 mm ⇒ 0.7% per year) and the fact that most bleeding aneurysms in routine practice are < 7-10 mm
    • it is assumed that some aneurysms walk through a period of higher risk of rupture after their formation and then stabilize and move into a period of low risk of rupture –  some of these aneurysms are likely to bleed shortly after their formation
    •  it makes sense to treat only incidental aneurysms that, for example, grow or change their shape
    • long-term stable aneurysms have a low risk of bleeding

ISUIA (International Study of Unruptured Intracranial Aneurysms) study is the largest and most widely discussed trial

  • n= 4060, three groups: no surgery x clipping x coiling
  • the larger the aneurysm, the greater the risk of rupture
  • higher risk for aneurysms in PCoA, PCA, and basilar artery
  • higher risk in patients with previous SAH from another source (approx. 10x)
  • the prospective arm (1991-1998) had an overall higher incidence of bleeding than the retrospective arm (1970-1991) – 0.8% vs. 0.3%
  • according to the prospective data, the risks of clipping and coiling are comparable, but coiling achieved complete obliteration in only 51% of cases
  • patients with aneurysms of the anterior circulation (MCA, ACoA) had better outcomes when they were clipped rather than coiled
  • the differences in the results of the retrospective and prospective arms make the generalization of the results problematic
  • according to many authors, the ISUIA study underestimates the risk of bleeding, as most ruptured aneurysms are 7-10 mm in diameter
The 5-year cumulative risk of rupture
anterior circulation
posterior circulation  (incl. PCoA)
< 7 mm 0% 2.5%
7-12 mm 2.6% 14.5%
13-24 mm 14.5% 18.4%
≥ 25 40% 50%

A rather conservative approach

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Rather surgical/interventional procedure

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  • first follow-up (MRA/CTA) in 6-12 months after the procedure, then every 1 or 2 years

Screening for asymptomatic aneurysms

  • generally not recommended (only grade C recommendations; cost-effectiveness is unknown)
  • screening is not recommended in the general population, even for smokers and alcoholics
  • screening is recommended for:
    • patients with previous aneurysmal SAH (higher risk of new aneurysm formation)
    • first-degree relatives of patients with aneurysmal SAH
  • more data are needed to help identify patients who would benefit from screening

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Management of asymptomatic intracranial aneurysm
link: https://www.stroke-manual.com/unruptured-intracranial-aneurysm-mangement/