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1. The blood supply enters the brain through the skull base via paired internal carotid and vertebral arteries.
2. Within the subarachnoid space these vessels communicate to form the Circle of Willis.
3. Subarachnoid haemorrhage occurs when a vessel ruptures into the subarachnoid layer.
4. The incidence of SAH is 6-16 per 100,000/year, representing 2-10% of all cerebrovascular events.
5. While in some countries SAH is predominantly traumatic in origin, in most cases these bleeds arise from ruptured aneurysms.


1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image: no reference available.

Ⓒ A. Manickam 2018

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