2.4 - Cerebral vasculature

Question 1

How much cardiac output, O2 and glucose consumption does the brain use?

Answer 1

• brain makes up 2% of body weight but uses:
• 10-20% of cardiac output
• 20% of body O2 consumption
• 66% of liver glucose

Question 2

What do the perfusion demands of the brain mean?

Answer 2

The brain is very vulnerable if the blood supply is impaired

Question 3

What two arteries supply the brain?

Answer 3

• internal carotid artery
• vertebral artery

Question 4

What is the blood supply to the brain from the heart (detail)?

Answer 4

• common carotid artery splits into external and internal carotid arteries at level of laryngeal prominence
• internal carotid artery goes through carotid canal into cranial cavity
• first branch of subclavian artery is vertebral artery, which goes through transverse foramen of cervical vertebrae and goes through foramen magnum into cranium

Question 5

How are the arteries of the brain arranged?

Answer 5

Circle of Willis and vertebrobasilar system

Question 6

What arteries do the internal carotid artery give rise to?

Answer 6

Anterior and middle cerebral arteries

Question 7

What are the arteries of the brain (top to bottom / front to back)?

Answer 7

• anterior communicating artery
• anterior cerebral artery
• internal carotid artery
• middle cerebral artery
• posterior communicating artery
• posterior cerebral artery
• basilar artery
• vertebral artery

Question 8

What is the advantage of the arrangement of the Circle of Willis?

Answer 8

If you have a blockage in one of the internal carotid arteries for example, there is a chance of compensatory flow from the other side

Question 9

What is the venous drainage of the brain?

Answer 9

Cerebral veins in brain drain into venous sinuses in the dura mater, which drains into the internal jugular vein

Question 10

How do the sinuses drain into the internal jugular vein?

Answer 10

• superior sagittal sinus / inferior sagittal sinus (along bottom of falx cerebri) / from great cerebral vein down straight sinus –> confluence of sinuses
• drains via transverse sinus into sigmoid sinus through jugular foramen –> becomes internal jugular vein

Question 11

What are the three meningeal layers from outside to inside?

Answer 11

• dura mater
• arachnoid mater
• pia mater

Question 12

What are the four types of intracranial haemorrhage?

Answer 12

• extradural
• subdural
• subarachnoid
• intracerebral

Question 13

What happens in an extradural haemorrhage?

Answer 13

• trauma, immediate clinical effects
• arterial, high pressure (often affects meningeal arteries/middle meningeal artery)
• common - fracture at pterion

Looks like a lemon on CT (convex-shaped) - epi –> pie –> lemon pie

Question 14

What happens in an subdural haemorrhage?

Answer 14

• trauma, can be delayed clinical effects
• venous, lower pressure (often affects veins draining into sinuses)

Looks like a banana on CT (concave-shaped) - suBdural –> Banana

RF: alcohol, elderly

Question 15

What happens in an subarachnoid haemorrhage?

Answer 15

• ruptured aneurysms
• usually happens near circle of Willis - burst due to aneurysm
• thunderclap headache

Question 16

What happens in an intracerebral haemorrhage?

Answer 16

Spontaneous hypertensive (often history of hypertension/atherosclerosis), sudden onset of focal neurological functions, essentially a haemorrhagic stroke

Question 17

What is a stroke AKA cerebrovascular accident (CVA)?

Answer 17

Rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration

Question 18

What are two causes of strokes?

Answer 18

• 85% are thrombo-embolic (blockage in vessels)
• 15% are haemorrhagic

Question 19

What is a transient ischaemic attack (TIA)?

Answer 19

Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours (essentially incomplete blockage, still get infarction)

Question 20

What is an infarction?

Answer 20

Degenerative changes which occur in tissue following occlusion of an artery (tissue loses blood supply)

Question 21

What is cerebral ischaemia?

Answer 21

• lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly (can result in infarction)
• lack of everything in blood, not just oxygen

Question 22

What is a thrombosis?

Answer 22

Formation of a blood clot (thrombus)

Question 23

What is an embolism?

Answer 23

• plugging of small vessel by material carried from larger vessel
• e.g. thrombi from heart, atherosclerotic debris from internal carotid
• fat and air (from syringe) could cause an embolism

Question 24

What are some stats about strokes?

Answer 24

• 3rd commonest cause of death
• 100k deaths in UK per annum
• 50% of survivors are permanently disabled
• 70% show obvious neurological deficit

Question 25

What are some risk factors for strokes? (5)

Answer 25

• age
• hypertension
• smoking
• cardiac disease
• diabetes mellitus

Question 26

What parts of the brain do the anterior cerebral artery perfuse?

Answer 26

Superomedial parts of the frontal lobe, anterior parietal lobe
(Think of it as affecting the middle part of top of head, like a mohawk)

Limbic lobe and insular cortex supplied

Question 27

What parts of the brain do the middle cerebral artery perfuse?

Answer 27

Majority of the lateral surface of the cerebral hemispheres, and the temporal pole (anterior end of temporal lobe)

Question 28

What parts of the brain do the posterior cerebral artery perfuse?

Answer 28

Occipital lobe, inferomedial surface of temporal lobe, midbrain, thalamus, choroid plexus of third and lateral ventricles

Question 29

What happens if there is damage to the anterior cerebral artery?

Answer 29

• paralysis of contralateral structures (leg > arm and face) - due to primary motor cortex damage
• disturbance of intellect, executive function and judgement (abulia = breakdown of frontal lobe function, due to frontal lobe damage)
• loss of appropriate social behaviour (frontal lobe damage)

Question 30

What happens if middle cerebral artery is damaged?

Answer 30

• ‘classic stroke’
• contralateral hemiplegia (paralysis) - arm > leg - due to motor cortex damage
• contralateral hemisensory deficits - due to somatosensory cortex damage
• hemianopia - loss of half of visual field - due to occipital lobe damage
• aphasia (left sided lesion, due to Broca’s/Wernicke’s damage)

Question 31

What happens if posterior cerebral artery is damaged?

Answer 31

• visual deficits
• homonymous hemianopia - cannot see
• visual agnosia - cannot interpret what we see
• due to occipital lobe damage

Question 32

What does yellow discolouration of walls in vessels indicate?

Answer 32

Build up of atheroma (fatty deposits) that cause atherosclerosis (hardening of arteries) - these deposits can break away and enter smaller vessels –> stroke