Is there screening for intracranial aneurysms, and which high‑risk individuals should undergo it?

Screening for Brain Aneurysms

Screening for intracranial aneurysms is NOT recommended for the general population, but IS recommended for specific high-risk groups, particularly those with two or more first-degree relatives with aneurysmal subarachnoid hemorrhage or unruptured intracranial aneurysms, and patients with autosomal dominant polycystic kidney disease (ADPKD). 1, 2

General Population Screening

• Routine screening of asymptomatic individuals in the general population is not supported by available evidence and should not be performed. 1
• The prevalence of intracranial aneurysms in the general population is approximately 1.8%, but the cost-effectiveness of screening has not been demonstrated in population-based clinical studies. 1
• Patients with environmental risk factors alone (cigarette smoking, alcohol use, hypertension) have an increased risk of subarachnoid hemorrhage but not a demonstrated increased frequency of intracranial aneurysms, and screening is not warranted in this population. 1

High-Risk Populations Who Should Be Screened

Familial Intracranial Aneurysm Syndrome

Patients with ≥2 first-degree relatives with aneurysmal subarachnoid hemorrhage or unruptured intracranial aneurysms should undergo screening (Class I recommendation, Level of Evidence B). 2, 1

• This population has an 8-11% prevalence of harboring an unruptured aneurysm, representing a 4-6.6 fold increased risk compared to the general population. 2, 3
• Risk factors that further increase detection likelihood include older age, female sex, cigarette smoking, hypertension, elevated lipid levels, and elevated fasting glucose. 2

Single First-Degree Relative with Aneurysm

For patients with only ONE first-degree relative with aneurysmal subarachnoid hemorrhage or unruptured intracranial aneurysm, screening may be reasonable if additional high-risk features are present. 2

• The risk of harboring an aneurysm is approximately 4% (relative risk 4.2) compared to 1.8% in the general population. 2, 4
• Consider screening if the patient has: current smoking, hypertension, female sex, age <50 years, or if the affected relative had multiple aneurysms. 2
• Cost-effectiveness analysis shows screening becomes unfavorable when age at screening is ≥50 years (incremental cost-effectiveness ratio >$50,000 per QALY). 2
• Recent evidence suggests screening may be beneficial even with one affected first-degree relative, particularly with serial screening over time, though current guidelines remain conservative. 4, 5

Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Patients with ADPKD should be offered screening due to a 10-11.5% prevalence of intracranial aneurysms, increasing to 21% if a first-degree relative also has an aneurysm history. 1, 5

• Aneurysmal subarachnoid hemorrhage occurs at a younger age in ADPKD patients compared to the general population. 1
• Screening has been shown to be cost-effective in multiple studies for this population. 1

Other High-Risk Conditions

Consider screening in patients with: 1

• Moyamoya disease
• Aortic dissection
• Bicuspid aortic valve
• Aortic aneurysm
• Coarctation of the aorta

Patients with Prior Treated Aneurysm

Patients previously treated for aneurysmal subarachnoid hemorrhage have a 1-2% annual rate of new aneurysm formation and should undergo periodic surveillance imaging. 1

Recommended Imaging Modalities for Screening

First-Line Screening: MRA Head Without Contrast

MRA of the head without intravenous contrast is the preferred initial screening modality. 2, 6, 7

• Demonstrates 95% sensitivity and 89% specificity for detecting intracranial aneurysms. 6, 7
• Non-invasive with no radiation exposure or contrast-related risks, making it ideal for serial screening. 6, 7
• 3T MRI scanners provide superior diagnostic accuracy compared to 1.5T systems, particularly for aneurysms <5 mm. 6, 7

Performance by aneurysm size: 6

• Aneurysms ≥5 mm: highest detection rate
• Aneurysms 3-5 mm: 45% of missed aneurysms fall in this range
• Aneurysms <3 mm: detection rate only 35-57%, representing 45% of all missed aneurysms

Alternative: CTA Head

CT angiography is an acceptable alternative screening modality. 1, 6

• Demonstrates >90% sensitivity and specificity, with ability to detect aneurysms as small as 2-3 mm (sensitivities 77-97%). 1, 6
• Requires intravenous contrast and radiation exposure, making it less ideal for long-term serial monitoring. 7
• Sensitivity decreases for aneurysms <3 mm and those adjacent to osseous structures. 1

Gold Standard: Catheter Angiography

Digital subtraction angiography remains the gold standard when it is clinically imperative to know if an aneurysm exists, but is not appropriate for screening due to its invasive nature. 1

• Risk of local catheter-related complications <5%, total neurological morbidity <1%, permanent neurological morbidity <0.5%. 1

Critical Pitfalls and Caveats

False Positives on MRA

Vessel loops and infundibular origins of vessels can mimic aneurysms on MRA, leading to false-positive interpretations. 1, 6, 7

• Requires experienced neuroradiological interpretation to avoid unnecessary interventions. 7

Limitations of Screening

• Only a minority of asymptomatic aneurysms rupture, and all aneurysm treatments carry inherent risks. 1
• The psychological impact and quality of life implications of living with a diagnosis of unruptured aneurysm have not been adequately evaluated. 1
• Screening identifies only a minority of all subarachnoid hemorrhage patients, as most cases occur in the general population related to hypertension and smoking. 3

Pre-Screening Counseling

Before screening, discuss with patients: 5, 3

• Benefits and downsides including risk of incidental findings
• Very small aneurysms requiring regular follow-up
• Preventive treatment risks and complications
• Anxiety associated with diagnosis
• Implications for driving licenses and life insurance

Risk Factor Modification Regardless of Screening

All patients, whether screened or not, should receive counseling on modifiable risk factors: 2, 6

• Smoking cessation is critical, as former smokers have lower relative risk than current smokers, with an inverse relationship between time since last cigarette and risk of subarachnoid hemorrhage. 1
• Blood pressure control for those with hypertension. 2, 6
• Limiting alcohol consumption. 6
• Education on warning symptoms of aneurysm rupture, particularly sudden severe "thunderclap" headache. 6