Cerebral Vasculature Flashcards
How much Cardiac Output does the brain use?
10-20%
How much O2 does the brain consume?
20%
How much liver glucose does the brain use?
66%
Why is the brain vulnerable when blood supply is impaired?
Due to it’s high metabolic demands
Which arteries supply the brain?
- Internal carotid (entry through the carotid canal)
- vertebral artery (foramen magnum)
Arteries in the brain?
The Circle of Willis
(2 x vertebral > basilar artery > posterior cerebral > posterior communicating > middle cerebral (internal carotid) > anterior cerebral > anterior communicating)
Where does atherosclerotic build-up occur most often in the cerebral arteries/circle of willis?
Where it divides.
What happens if there is an effective blockage of the cerebral arteries in the Circle of Willis?
Theoretical chance of compensatory flow from the other side.
Realistically compensation between the posterior and anterior cerebral arteries is weak as P communicating are very thin.
Venous drainage of the brain?
Drains mainly through venous sinuses in the dura mater (through the cerebral veins) > internal jugular vein
Order of venous drainage through the sinuses?
superior (+inferior) sagittal sinus + straight sinus> confluence of sinuses > sigmoid sinus (lateral/transverse drainage)
What are the different types of intracranial haemorrhage
- extradural
- subdural
- subarachnoid
- intracerebral
Where do sinuses form?
In between the meningeal (inner) and periosteal (outer) layers of the dura mater
What causes a extradural cranial haemorrhage?
- trauma
- high pressure arterial bleed
What causes a subdural cranial haemorrhage?
- trauma
- low pressure, venous bleed
What causes a subarachnoid cranial haemorrhage?
Ruptured aneurysms
(normally congenital)
- blood vessel weakness
- may burst in hypertensive patients
What causes a intracerebral cranial haemorrhage?
- spontaneous hypertensive
normal in chronic hypertensives
Where is a fragile point in the head?
Pterion
Why is the Pterion so vulnerable?
Protects the artery supplying the dura (if ruptured causes an extradural bleed)
Where do Extradural bleeds occur?
Between the dura and the skull, builds up pressure (arterial)
How do extradural bleeds present?
- Acute onset
- surgical emergency
- high intracranial pressure
Where do subdural bleeds occur?
Between the dura and the arachnoid.
small amount of space
How do subdural bleeds present?
- Delayed onset of symptoms
- venous, lower pressure bleed
Where do subarachnoid haemorrhages most commonly occur?
- Base of the brain, near the circle of willis
Stroke Definition
(CVA)
cerebrovascular accident
rapidly developing disturbance of brain function of a presumed vascular origin for >24 hours
What does a rapid onset stroke indicate?
Likely vascular origin
exclusion of differentials must occur
What is a thrombo-embolic stroke and how common is it?
Stroke due to blockages
85% of strokes
What is a haemorrhage stroke and how common is it?
Stroke due to brain bleed
15% of strokes
Transient Ischaemic Attack (TIA)
same as stroke but resolved in 24 hours
(no residual deficits)
rapidly developing focal disturbance of brain function of a presumed vascular origin that completely resolves in 24 hours
TIA time span?
normally can be from 30 seconds - 1 minute
What does a TIA indicate?
Subsequent stroke further down the line
cause of TIA may worsen
Infarction
Degenerative tissues that occur in the tissue due to occlusion of an artery (tissue death)
Cerebral Ischaemia
Lack of sufficient blood supply to nervous tissue which leads to permanent damage if blood supply is not restored quickly.
How is Ischaemia different from hypoxia?
Ischaemia is a lack of everything, not just O2
Thrombosis definition
Formation of a blood clot (thrombus)
can be a form of embolism
Embolism definition
Plugging of a small vessel by material carried from a larger vessel
Examples of embolism
- thrombi from the heart
- atherosclerotic debris from the internal carotid
- fat
- air (IV injections)
Strokes and Public Health
- 3rd most common cause of death (100,000 deaths/year)
- 50% of survivors are permanently disabled
- 70% show an obvious neurological deficit
Risk Factors of Stroke
- Age
- Hypertension
- Cardiac Disease
- Smoking
- Diabetes Mellitus (effects on vasculature)
Where does the Anterior Cerebral artery perfuse?
- midline structures (about 1cm strip)
- all the way back to the parietal-occipital fissure
Where does the Middle Cerebral artery perfuse?
- most of lateral surface of the brain
- most of the subcortical (deep) structures in the brain
Where does the Posterior Cerebral artery perfuse?
- mostly the occipital lobe
- inferior part of the temporal lobe
Symptoms of stroke of the Anterior Cerebral Artery
- paralysis of contralateral structures (opposite to the perfusion of brain)
(most likely the leg) - front lobe damage, disturbance of intellect, executive function and judgement (abulia - decreased frontal function)
also, possible loss of appropriate social behaviour.
Symptoms of a Middle Cerebral Artery stroke?
‘Classic Stroke’
- (deep motor structures): contralateral hemiplegia (arm>leg)
- (sensory cortex): contralateral hemisensory deficits.
- (runs from eye to occipital) Hemianopia (loss of half the visual field)
- Aphasia, lack of normal speech (Left-sided lesion)
Symptoms of a Posterior Cerebral Artery stroke
- The occipital region of the brain Visual Deficits: - Homonymous hemianopia - Visual Agnosia - Prosop Agnosia (unable to recognise faces)
Indication of Infarction
Loss of clear differentiation between white and grey matter.
