Blood supply to the brain Flashcards
What does this CT show
Subarachnoid haemorrhage
Describe the blood supply to the brain
The brain has an anterior and posterior circulation
* Anterior: supplied by paired internal carotid arteries
* Posterior: supplied by the basilar artery, formed by the convergence of the two vertebral arteries
* Anterior and posterior circulations are joined by the anterior and posterior communicating arteries which form an anastomosis known as the circle of Willis
Describe the Circle of Willis (origin, surrounding structures, branches)
- Formed by the anastamosis of the anterior and posterior communicating arteries
- Located in the interpeduncular cistern at the base of the brain. Surrounds the optic chiasm, pituitary stalk, mamillary bodies
- 3 main arteries arising from the circle of Willis: anterior, middle (from the internal carotid arteries) and posterior cerebral arteries (from the vertebrobasilar system
What are the most common locations for cerebral aneurysms?
Cerebral aneurysms are saccular out-pouchings of the cerebral arteries.
Approx 85% develop in the anterior part of the Circle of Willis, and involve the internal carotid arteries (i.e. anterior and middle sections of brain)
* Anterior communicating artery: 30-35%
* Bifurcation of the internal carotid and posterior communicating artery: 30-35%
* Bifurcation of the middle cerebral artery: 20%
* Bifurcation of the basilar artery, and the remaining posterior circulation arteries: 10%
Which areas of the brain are most at risk from ischaemia during periods of systemic hypotension?
The deep penetrating branches of the main cerebral arteries are functional end arteries, althouth there are some anastomoses between distal branches
-> the boundary zones between the areas supplied by individual arteries are most at risk from systemic hypotension (watershed zones -> watershed infarcts)
Describe the cerebral venous drainage
The cerebral venous system consists of:
* **Superficial **system: saggital sinuses and cortical veins, which drain superficial surfaces of both cerebral hemispheres
* Deep system: lateral sinus, straight sinus, sigmoid sinus, and draining deeper corticla veins
Both drain into the internal jugular veins