Etiology

Nontraumatic SAH usually results from the rupture of an abnormal arterial vessel and subsequent bleeding onto the surface of the brain. Ruptured saccular aneurysms of the basal vessels of the brain account for 77% of nontraumatic SAH. Arterio-venous malformations account for another 10% of cases.

Evidence suggests a multifactorial etiology that involves both genetic and acquired factors.

Genetic factors:

• Cerebral aneurysms are associated with genetic abnormalities
  • Autosomal dominant polycystic kidney disease
  • Ehlers-Danlos syndrome type IV
  • Fibromuscular dysplasia
  • Arterio-venous malformations
  • Coarctation of the aorta
  • Marfan syndrome
• Familial clusters
• Multiple aneurysms frequent in SAH patients

Accquired factors:

• infection
• vasculitis
• neoplasms
• atherosclerosis
• hemodynamic stress
• smoking
• alcohol and drug abuse
• hypertension

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