Management of asymptomatic intracranial aneurysm

Created 31/03/2021, last revision 06/11/2023

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 Pheochromocytoma Marfan syndrome α1-antitrypsin deficiency	age > 50 years smoking alcohol abuse cocaine or amphetamine abuse atherosclerosis head trauma

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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)

UIA score

The unruptured intracranial aneurysm treatment score [Etminan, 2015]

→ UIA score calculator

PHASES score

PHASES score – prediction of the risk of aneurysm rupture [Greving, 2013]
Age
< 70 y ≥ 70 y	0 1
Hypertension
no yes	0 1
Aneurysm size
< 7 mm 7-9.9 mm 10-19.9 mm > 20 mm	0 3 6 10
Previous SAH
no yes	0 1
Aneurysm location
ICA MCA ACA, PCA, PComA, and posterior circulation	0 2 4
Population
Finnish Japanese Other	5 3 0

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%

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

generally not recommended (only grade C recommendations; cost-effectiveness is unknown)
screening is not recommended in the general population, even for smokers and alcoholics
- may be considered in female smokers 30-60 years of age [Ogilvy, 2020]
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