2.4 - Cerebral vasculature Flashcards
How much cardiac output, O2 and glucose consumption does the brain use?
- brain makes up 2% of body weight but uses:
- 10-20% of cardiac output
- 20% of body O2 consumption
- 66% of liver glucose
What do the perfusion demands of the brain mean?
The brain is very vulnerable if the blood supply is impaired
What two arteries supply the brain?
- internal carotid artery
- vertebral artery
What is the blood supply to the brain from the heart (detail)?
- 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
How are the arteries of the brain arranged?
Circle of Willis and vertebrobasilar system
What arteries do the internal carotid artery give rise to?
Anterior and middle cerebral arteries
What are the arteries of the brain (top to bottom / front to back)?
- anterior communicating artery
- anterior cerebral artery
- internal carotid artery
- middle cerebral artery
- posterior communicating artery
- posterior cerebral artery
- basilar artery
- vertebral artery
What is the advantage of the arrangement of the Circle of Willis?
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
What is the venous drainage of the brain?
Cerebral veins in brain drain into venous sinuses in the dura mater, which drains into the internal jugular vein
How do the sinuses drain into the internal jugular vein?
- 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
What are the three meningeal layers from outside to inside?
- dura mater
- arachnoid mater
- pia mater
What are the four types of intracranial haemorrhage?
- extradural
- subdural
- subarachnoid
- intracerebral
What happens in an extradural haemorrhage?
- 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
What happens in an subdural haemorrhage?
- 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
What happens in an subarachnoid haemorrhage?
- ruptured aneurysms
- usually happens near circle of Willis - burst due to aneurysm
- thunderclap headache
What happens in an intracerebral haemorrhage?
Spontaneous hypertensive (often history of hypertension/atherosclerosis), sudden onset of focal neurological functions, essentially a haemorrhagic stroke
What is a stroke AKA cerebrovascular accident (CVA)?
Rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration
What are two causes of strokes?
- 85% are thrombo-embolic (blockage in vessels)
- 15% are haemorrhagic
What is a transient ischaemic attack (TIA)?
Rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours (essentially incomplete blockage, still get infarction)
What is an infarction?
Degenerative changes which occur in tissue following occlusion of an artery (tissue loses blood supply)
What is cerebral ischaemia?
- 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
What is a thrombosis?
Formation of a blood clot (thrombus)
What is an embolism?
- 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
What are some stats about strokes?
- 3rd commonest cause of death
- 100k deaths in UK per annum
- 50% of survivors are permanently disabled
- 70% show obvious neurological deficit
What are some risk factors for strokes? (5)
- age
- hypertension
- smoking
- cardiac disease
- diabetes mellitus
What parts of the brain do the anterior cerebral artery perfuse?
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
What parts of the brain do the middle cerebral artery perfuse?
Majority of the lateral surface of the cerebral hemispheres, and the temporal pole (anterior end of temporal lobe)
What parts of the brain do the posterior cerebral artery perfuse?
Occipital lobe, inferomedial surface of temporal lobe, midbrain, thalamus, choroid plexus of third and lateral ventricles
What happens if there is damage to the anterior cerebral artery?
- 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)
What happens if middle cerebral artery is damaged?
- ‘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)
What happens if posterior cerebral artery is damaged?
- visual deficits
- homonymous hemianopia - cannot see
- visual agnosia - cannot interpret what we see
- due to occipital lobe damage
What does yellow discolouration of walls in vessels indicate?
Build up of atheroma (fatty deposits) that cause atherosclerosis (hardening of arteries) - these deposits can break away and enter smaller vessels –> stroke
