Description

• Bleeding into the subarachnoid space and CSF:
  • Spontaneous:
    • Results from ruptured cerebral artery aneurysm in up to 80% of cases
    • Aneurysms that are >25 mm are more likely to rupture
  • Traumatic:
    • Represents severe head injury

Epidemiology

• Incidence is 6–16 per 100,000 individuals
• Affects 21,000 in the U.S. annually
• Associated mortality in 30–50% of patients with 1 in 4 dying within 1 d
• Uncommon prior to third decade of life; incidence peaks in sixth decade

Risk Factors

• Aneurysms ≥7 mm have greater risk for rupture
• After adjustment for size and location, aneurysm aspect ratio >1.3 and irregular shape also significantly associated with rupture
• Family history
• Hypertension
• Smoking
• Alcohol abuse
• Sympathomimetic drugs:
  • Cocaine, methamphetamine, and ecstasy (MDMA)
• Gender (female:male 1.6:1)

• Three- to sevenfold increased risk in first-degree relatives with subarachnoid hemorrhage (SAH)
• Strongest genetic association represents only 2% of SAH patients:
  • Autosomal dominant polycystic kidney disease, Ehlers–Danlos type IV, familial intracranial aneurysms

• Most often due to arteriovenous malformation in children
• Although rare in children, SAH is a leading cause of pediatric stroke

Etiology

• “Congenital,” saccular, or berry aneurysm rupture (80–90%):
  • Occur at bifurcations of major arteries
  • Incidence increases with age
  • Aneurysms may be multiple in 20–30%
• Nonaneurysmal perimesencephalic hemorrhage (10%)
• Remaining 5% of causes include:
  • Mycotic (septic) aneurysm due to syphilis or endocarditis
  • Arteriovenous malformations
  • Vertebral or carotid artery dissection
  • Intracranial neoplasm
  • Pituitary apoplexy
• Severe closed head injury