Who is at risk for a subarachnoid hemorrhage?

Risk Factors for Subarachnoid Hemorrhage

Hypertension, smoking, and heavy alcohol use are the most significant modifiable risk factors for subarachnoid hemorrhage (SAH), while family history and certain genetic conditions represent important non-modifiable risk factors. 1

Major Risk Factors

Modifiable Risk Factors

1. Hypertension

   • Increases risk approximately 2.9 times 1, 2
   • Accounts for approximately 17% of all SAH cases 3
   • Blood pressure control is recommended to reduce risk 1

2. Smoking

   • One of the strongest modifiable risk factors
   • Increases risk 3-3.5 times 1, 2
   • Accounts for approximately 20% of all SAH cases 3
   • Cessation is strongly recommended to reduce SAH risk 1

3. Alcohol Consumption

   • Heavy alcohol use (≥300g/week) increases risk 4.7 times 2
   • Moderate alcohol use (100-299g/week) accounts for 11% of cases 3
   • Heavy alcohol use accounts for 21% of cases 3

Non-Modifiable Risk Factors

1. Family History

   • Having ≥2 first-degree relatives with intracranial aneurysms increases risk 4.2 times 1
   • Accounts for approximately 11% of all SAH cases 3
   • Familial intracranial aneurysm syndrome is associated with:
     • Younger age at SAH occurrence
     • Higher incidence of multiple aneurysms
     • Hemorrhages among siblings and mother-daughter pairs 1

2. Genetic Conditions

   • Autosomal dominant polycystic kidney disease 1
   • Type IV Ehlers-Danlos syndrome 1
   • Accounts for approximately 0.3% of all SAH cases 3

3. Demographic Factors

   • Female sex (1.24 times higher risk than men) 1
   • Age (typical onset around 50 years, with increasing incidence with age) 1
   • Race/ethnicity (higher incidence in Blacks and Hispanics compared to white Americans) 1

Combined Risk Factors

The joint effect of multiple risk factors is particularly important:

• Smoking + Hypertension: Creates a synergistic effect with 8.3 times increased risk for intracranial aneurysms 4
• In individuals with family history of SAH, the additional risk from smoking and hypertension is 2.7 times 5

Protective Factors

Some evidence suggests that the following may reduce risk:

• Regular physical exercise (OR 0.6) 4
• Hypercholesterolemia (OR 0.5) 4 (though this finding requires further investigation)

High-Risk Populations Requiring Special Consideration

1. Individuals with family history

   • Those with ≥2 first-degree relatives with intracranial aneurysms have 10.5% prevalence of aneurysms 1
   • Screening may be considered for these high-risk individuals 1

2. Patients with prior aneurysmal SAH

   • Annual rate of new aneurysm formation is 1-2% per year 1
   • Higher risk in those with multiple intracranial aneurysms 1

3. Drug users

   • Sympathomimetic drugs including cocaine increase risk 1
   • Cocaine-related SAH tends to occur in younger patients 1

Screening Considerations

• Radiological screening is cost-effective when performed every 5-7 years for individuals 20-80 years of age with ≥2 first-degree relatives with known cerebral aneurysms 1
• When screening is indicated, MRA combined with CT angiography provides good detection, though catheter angiography remains the gold standard when definitive diagnosis is needed 1

Clinical Implications

The significant economic and societal burden of SAH (with hospital costs exceeding $373,000 per case) 1 underscores the importance of risk factor modification. Since many cases of SAH are preventable through lifestyle changes, clinicians should aggressively target modifiable risk factors, particularly in those with family history or other non-modifiable risk factors.

Healthcare providers should prioritize:

• Blood pressure control
• Smoking cessation counseling and support
• Alcohol reduction strategies
• Consideration of screening in high-risk individuals

By addressing these risk factors, a substantial proportion of SAH cases could potentially be prevented, significantly reducing morbidity and mortality from this devastating condition.