Blood supply to the brain

Question 1

What does this CT show

Answer 1

Subarachnoid haemorrhage

Question 2

Describe the blood supply to the brain

Answer 2

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

Question 3

Describe the Circle of Willis (origin, surrounding structures, branches)

Answer 3

• 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

Question 4

What are the most common locations for cerebral aneurysms?

Answer 4

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%

Question 5

Which areas of the brain are most at risk from ischaemia during periods of systemic hypotension?

Answer 5

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)

Question 6

Describe the cerebral venous drainage

Answer 6

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

Question 7

Answer 7

Question 8

Answer 8