Subarachnoid Hemorrhage: Causes

Pathogenesis (development of disease)

In the setting of aneurysm rupture (rupture of a pathologic/diseased bulge in an arterial wall within the skull), which is the most common cause of subarachnoid hemorrhage, hemorrhage occurs into the fluid-filled subarachnoid space (i.e., hemorrhage outside the brain). The subarachnoid space surrounds the brain (Latin cerebrum) and spinal cord (Latin medulla spinalis or medulla dorsalis) and is filled with cerebrospinal fluid (CSF). It is a cleft space between the arachnoid mater (cobweb skin; middle meninges) and the pia mater (delicate meninges that rest directly on the brain). The massive hemorrhage increases intracranial pressure (ICP; intracranial pressure), which explains the sudden onset of a very severe headache. At the same time, cerebral blood flow drops and perfusion pressure (pressure with which a tissue is perfused) decreases. As a result, the patient loses consciousness. After a short time, reactive hyperemia occurs, which means that blood flow increases again and the patient regains consciousness. Large accumulations of blood cause adhesions in the basal cisterns (= cavities around the brain; they contain the cerebrospinal fluid), which impairs the passage of the cerebrospinal fluid (CSF). Hydrocephalus (abnormal dilation of the CSF-filled fluid spaces (cerebral ventricles) of the brain) may develop. Vasospasm (vascular spasm) occurs in the arteries of the pia mater. The risk of this is highest from day 4 to day 10. Because of chronic constriction, there is reduced perfusion (reduced supply) to the brain and cerebral damage (ischemia).

Etiology (Causes)

Nontraumatic (spontaneous) subarachnoid hemorrhage.

  • Aneurysmal SAB (85% of cases) – In about one-third of cases, physical exertion causes rupture of the aneurysm; in the other cases, the affected person is at rest.
    • Localization of aneurysms:
      • 80-90% of aneurysms are located in the anterior cerebral circulation: Internal carotid artery, anterior cerebral artery, middle cerebral artery and its branches
      • 10-20% of aneurysms are located in the posterior cerebral circulation: A. vertebralis, A. basilaris, A. cerebri posterior and their branches.
    • Behavioral causes
      • Consumption of stimulants
        • Alcohol abuse (alcohol dependence)
        • Tobacco (smoking)
    • Causes related to disease
      • Hypertension (high blood pressure)
  • Non-aneurysmal SAB (15% of cases).
    • Disease-related causes
      • Arteriitis (inflammation of one or more arteries).
      • Vascular anomalies such as arteriovenous malformation (AVM; congenital malformation of blood vessels), durafistula (pathological short-circuit connection between arteries and veins at the level of the meninges)
      • Intracranial (occurring in the skull) arterial dissection (splitting of the wall layers of an artery).
      • Cocaine abuse
      • Venous thrombosis (vascular disease in which a blood clot (thrombus) forms in a vein).
      • Reversible cerebral vasoconstriction syndrome (RCVS; synonym: Call-Fleming syndrome: constriction (contraction of muscles) of cerebral vessels leading to severe headache (annihilation headache) with or without other neurologic abnormalities)
      • Tumors
      • Cerebral amyloid angiopathy (ZAA) – degenerative vasculopathy (vascular damage) resulting from deposits of beta-amyloid (peptides/determined protein molecules) in wall layers; beta-amyloid plaques are also thought to be a major cause of dementia and Alzheimer’s disease

Traumatic subarachnoid hemorrhage