At autopsy intracranial aneurysms are found in approximately 1% of the population. Aneurysm rupture occurs in 6-12 per 100 000 per year
<40 years, male > females but this ratio varies with age — > 40 years, females > males
Inheritance: familial occurrence is occasionally seen and is probably associated with procollagen III deficiency, although other factors may be involved. Age: rupture is most common between 40 and 60 years but can occur in any age group, though rarely in children.
Intracranial aneurysms are usually saccular,----------
occurring at vessel bifurcations.
Size varies from a few millimetres to several centimetres. Those over 2.5 cm are termed 'giant' aneurysms.
Fusiform dilatation and ectasia of the carotid the basilar artery may follow atherosclerotic damage. These aneurysms seldom rupture.
Mycotic aneurysms, secondary to vessel wall infection, arise from haematogenous spread, e.g. subacute bacterial endocarditis. Aneurysm rupture: usually occurs at the fundus of the aneurysm and the risk appears to be related to size; rupture seldom occurs until the aneurysm is over 6 mm in diameter. In some patients, rupture occurs during exertion, straining or coitus, but in many there is no associated relationship. Giant aneurysms surprisingly are less likely to rupture, probably due to multiple layers of thrombus reinforcing the inner wall.
Sites of saccular aneurysm
\ Blood flow and
\ Blood flow
Middle cerebral artery trifurcation and bifurcation
Posterior circulation .-Basilar artery ^Posterior inferior cerebellar artery
35-40% Anterior cerebral artery
- 30% Internal' carotid artery
Anterior communicating artery (Pericallosal artery)
Posterior communicating artery Carotid bifurcation (Anterior choroidal artery) (Ophthalmic artery)
Multiple aneurysms: in approximately 30% of patients with aneurysmal SAH, more than one aneurysm is demonstrated on angiography.
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