Cerebral vasculature Flashcards
why is the brain v vulnerable if blood supply is impaired?
Although brain makes up 2% of total body weight it uses:
10-20% cardiac output,
20% body O2 consumption , 66% liver glucose
if these requirements aren’t met braincells may infarct
What structures supply blood to the brain and where do they come from
1) Vertebral artery ( right comes from R subclavian artery –> branch of the brachiocephalic artery . L from left subclavian artery.
2) Internal carotid arteries which split into common carotid at laryngeal prominence ( R comes from r common carotid –> branch of the brachiocephalic artery. L from left common carotid )
What are the 3 branches of the aorta
Brachiocephalic artery
left subclavian
left common carotid
What are the branches of the brachiocephalic artery
R common carotid ( giving internal + external carotid) + R subclavian ( giving vertebral artery
Which foramen does the vertebral artery pass through
transverse foramen on vertebral body
Where does the internal and external carotid artery bifurcate from the common carotid artery
level of laryngeal prominence
What is the circle of willis
Circle of blood vessels in the brain
What are the 2 main arteries that feed the circle of willis
internal carotid + vertebral
Describe the circle of willis
See image on docs
Where does the basilar artery sit
on the base of the pons
What does the middle , anterior and posterior cerebral artery supply
middle –> temporal + parietal lobes
anterior –> frontal +superior medial parietal lobes)
Posterior –> occipital + inferior temporal lobes
Why is the circle of willis beneficial
can avoid blockage in any major artery ( ie internal carotid) due to compensatory flow form the other side
though not universal as communicating arteries are thin
How are sinuses created
Due to separation of periosteal and meningeal layers of the dura
What does the superior , straight and occipital sinus drain into
Confluence of sinuses
What does the confluence of sinus drain into
Transverse sinus then to sigmoid sinus
What does the signmoid sinus drain into
Internal jugular vein
What is the order of venous drainage in the brain
1) sagittal sinus
2) Confluence of sinuses
3) Transverse sinus
4) sigmoid sinus
5) IJV ( internal jugular)
name the 3 layers of meninges in the brain
Dura ( periosteal , meningeal. Infoldings form falx cerebri + falx cerebelli
arachnoid mater : Subarachnoid space has CSF –> collapses onto brain if CSF not there
pia mater
What are the 4 types of haemorrhage
Extradural
subdrual
subarachnoid
intracerebral
What causes extradural bleeds
Trauma often to the pterion region damaging middle meningeal artery
Why are extradural haemorrhage so dangerous
As arterial high pressure bleed. can increase intercranial pressure ( stripping periosteal layer away from bone) and compress brainstem
Will have immediate clinical effects
How to spot extradural haemorrhage
lemon shaped spot in MRI/CT
What causes subdural bleeds
ruptured veins in brain
Why are subdural bleeds less dangerous than extradural bleeds
Extradural due to high pressure arterial bleed , subdural is a venous bleed at lower pressure so less blood loss
What should you do clinically with a patient who might have a subdural bleed
Keep patient in hospital overnight and monitor esp if head injury causes confusion / loss of consciousness as subdural bleeds present with delayed symptoms that can present overnight
What causes subarachnoid bleeds
Ruptured aneurysms ( often in lower brain in circle of willis
Risk factors for subarachnoid bleeds
Congenital aneurisms
hypertension
Causes of intracerebral bleeds
Spontaneous rupture of artery due to hypertension
What is a stroke
type of cerebrovascular accident (CVA) aka rapidly developing focal disturbance of brain function of presumed vascular origin and >24 h duration
What causes CVAs ( cerebrovascular accidents
15% haemorrhage
85% thrombo- embolic ( blockage in vessels
What are the 4 types of stroke
Ischemic
haemorrhagic
transient ischaemic
thromboembolic
What is an ischaemic stroke
occurs when blood flow is blocked by a clot or an embolism
What is haemorrhagic stroke
Occurs due to bursting of a blood vessel
what is transient ischaemic stoke
Occurs when disruption of circulation to one part of brain due to thromboembolic causes . Resolves in 24h
What is a thrombosis
formation of blood clot
What is embolism
Plugging of small vessel by material ( atherosclerotic debris) is carried from a larger vessel
What is a thromboembolism
formation of a thrombus elsewhere within circulation can be degenerated into an embolus, being carried within circulation into cerebral arteries.
Atherosclerotic debris from the internal carotid artery can further contribute to the development of a thrombo-embolic stroke
An arterial gas embolism can form within blood vessels, and travel into cerebral vasculature, potentially causing a stroke
symptoms for stoke
Think FAST Face --> cant smile , one side fallen Arms --> can't hold them up speech --> slurred time --> call 999
Risk factors for stroke
Age Hypertension Cardiac disease Smoking Diabetes mellitus
What does the anterior, middle and posterior cerebral artery supply
1) ant --> Supplies the para-sagittal midline of the brain and perfuses the occipital fissure Includes PMC ( premotor cortex)
2) middle –> supplies a portion of the frontal lobe and the lateral surface of the temporal and parietal lobes + deep structures of the brain
Includes PMC
3) post –> supplying the occipital lobe, in addition to the inferior region of the temporal lobe
Symptoms of anterior cerebral artery stroke
Disruption to ACA supply impacts contralateral motor control, subsequently leading to paralysis.
This is due to it effecting the PMC which is sematosensory ( different areas are mapped to different parts of the body)
Topographically, paralysis of the leg > arm, face.
Disturbance of intellect, executive function, and judgement (abulia).
Abulia = broken down frontal function
Loss of appropriate social behaviour (disinhibition).
2 + 3 due to damage to frontal lobe
Symptoms of middle cerebral artery stroke
Classic stroke leads to contralateral hemiplegia, topographically affecting the arm > leg.
As effects motor cortex and deep motor association structures
hemiplegia= paralysis on one sde of teh body
Contralateral hemisensory deficits (damage to primary somatosensory cortex residing in the post central gyrus).
Hemianopia ( loss of one half of visual field→ Ocular systems runs back to occipital lobe which can be damaged )
Aphasia (In a left sided lesion): Broca’s and Wernicke’s area affected.
Symptoms of post cerebral artery stroke
A stroke will lead to visual deficits: Homonymous hemianopia (One side) and visual agnosia (inability to recognise).
Due to damage to occipital lobe so loss of visual field and processing
Prosopagnosia is a cognitive disorder of face perception. ( aka inability to recognise faces of ppl you’ve known for a long time)
