Arterial and Venous supply to the brain

Question 1

the venous supply of the brain?

Answer 1

• the venous blood and cerebral spinal fluid in the brain drain into the dural venous sinuses
• dural sinuses derive from the folds of the meninges
• dura sinuses are similar to veins, but they lack valves
• venous blood from dura sinuses drains towards the internal jugular veins (which merges with the subclavian vein to form the brachiocephalic vein)
• both left and right brachiocephalic veins join to form the SVC which empties into the RA of the heart

Question 2

internal carotid arteries supply the anterior 2/3rds of which part of the brain?

Answer 2

the cerebral hemispheres and the basal ganglia (via lenticulostriate arteries).
- an internal carotid artery occlusion causes total infarction of these areas.

Question 3

what is the circle of willis?

Answer 3

an anastomotic ring at the base of the brain fed by the 3 arteries that supply the brain with blood:
- the internal carotids (anteriorly)
- the basilar artery (posteriorly, formed by joining of the vertebral arteries which supply brainstem)

Question 4

what 3 paired arteries leave the circle of willis to supply the cerebral hemispheres?

Answer 4

• anterior
• middle
• posterior cerebral arteries

anterior and middle being branches of internal carotid arteries
basilar artery dividing into 2 posterior arteries
-> occlusion of any one of them is lessened by the retrograde supply from leptomeningeal vessels

Question 5

what does anterior cerebral artery supply?

Answer 5

• supplies the frontal and medial part of the cererbum
  -> occlusion may cause a weak, numb contralateral leg +- similar, if milder, arm symptoms. face is spared. bilateral infarction is a rare cause of paraplegia ad even rarer cause of akinetic mutism

Question 6

what does middle cerebral artery supply?

Answer 6

• supplies the lateral part of each hemisphere.
• occlusion may cause contralateral hemiparesis, hemisensory loss (esp. face and arm), contralateral homonymous hemianopia due to involvement of optic radiation, cognitive change including dysphasia w dominant hemisphere lesions, and visuospatial disturbance e.g. can’t dress, gets lost with non-dominant lesions

Question 7

what does the posterior cerebral artery supply?

Answer 7

• supplies the occipital lobe. occlusion gives contralateral homonymous hemianopia (often w macular sparing)

Question 8

what does the vertebrobasilar circulation supply?

Answer 8

• cerebellum
• brainstem
• occipital lobes

signs of occlusion
-> vision problems
-> vertigo, nystagmus
-> dysarthria, dysphasia
-> hemi or quadriplegia

Question 9

what is subclavian steal syndrome?

Answer 9

• subclavian artery stenosis proximal to the origin of the vertebral artery may cause blood to be stolen by retrograde flow down this vertebral artery down into the arm, causing brainstem ischaemia typically after use of the arm
• suspect if BP in each arm differs by >20mmHg

‘dizzy-plus’ syndromes and arterial events
SCA -> dizzy
AICA -> dizzy and deaf
PICA -> dizzy, dysphagic, and dysphonic (abnormal voice) - this is the largest branch of the vertebral artery and is one of the 3 main arteries supplying the cerebellum

Question 10

where does a berry aneurysm most often occur?

Answer 10

• saccular or ‘berry’ aneurysm occurs most frequently within the circle of willis vasculature
• they are the most common cause of non-traumatic subarachnoid haemorrhage
• (1) being the most common site

Question 11

what arteries supply the dura mater?

Answer 11

• anterior and posterior meningeal arteries

Question 12

what arteries supply the spinal cord?

Answer 12

• anterior and posterior spinal arteries

Question 13

what paired set of arteries converge to form the basilar artery at the base of the pons?

Answer 13

vertebral arteries

Question 14

which direction does basilar artery run?

Answer 14

it runs superiorly within the groove of the pons, giving off a no of branches including the pontine arteries, which supply the pons.

eventually anastomoses w the circle of willis via the posterior cerebral arteries and posterior communicating arteries?

Question 15

what is locked-in syndrome?

Answer 15

pontine infarcts cause an interruption in the myriad of neuronal pathways enabling communication between cerebrum, cerebellum, spinal cord…
this can result in complete paralysis of all voluntary muscle groups, sparing those controlling the eyes.
those suffering from damage to pons are fully conscious and cognitively intact

Question 16

circle of willis diagram

Answer 16

Question 17

what is the treatment for a ‘berry aneurysm’?

Answer 17

• tx involves urgent neosurgical referral and subsequent endovascular coiling or inserting a surgical clip to occlude flow to an aneurysm

Question 18

an aneurysm in the posterior communicating artery causes what cranial nerve palsy?

Answer 18

• third cranial nerve palsy
• due to its close anatomical relationship
• external compression of third nerve affects parasympathetic fibres surrounding outermost region of third nerve - inability to constrict pupil - making it appear fixed and dilated ‘blown pupil’
• vaso vasorum, central area of 3rd cranial nerve - when this is damage - pupillary involvement
  -> diabetes and atherosclerosis can cause this