27. Blood supply to the brain Flashcards
How do cerebral arteries differ from normal ones?
Thinner walls
Much more easily blocked
Do not have the same amount of elastic and smooth muscle
Look very similar to veins
How do cerebral veins differ from normal ones?
Thin walled
No valves present
Look very similar to arteries
Reliant on gravity for the removal of venous blood from the brain
Where the blood supply to the anterior part of the brain come from?
Internal carotid arteries - gives way to the middle and anterior cerebral arteries
This is 80% of cerebral blood flow
Where does the blood supply to the posterior part of the brain come from?
From the subclavian arteries (origin of the vertebral arteries)
Join to form the basillar artery and posterior cerebral artery branches from here
This is the remaining 20% of cerebral blood flow
DRAW CIRLCE OF WILLIS
DRAW CIRLCE OF WILLIS
What is the biggest branch of the internal carotid artery?
The middle cerebral artery
What are the lenticulostriate arteries?
These are the arteries that provide the basal ganglia and the internal capsule
Branches of the middle cerebral
Where in the brain do the different cerebral arteries supply?
Anterior - medial superior
Middle - Lateral region of the brain
Posterior - medial inferior
What foramina do the vertebral arteries pass through and what do they then form?
Vertebral arteries through the foramen magnum then form the basillar artery
What part of the brain does the basillar artery supply?
The pons (pontine branches)
What part of the brain does the posterior cerebral artery supply?
Midbrain
Thalamus and internal capsule
Inferior and medial aspects of the occipital cortex
What are bridging veins?
These are veins which pierce through the dura to allow venous drainage
What other structure can pierce the dura and what is their function?
Arachnoid granulations - these pierce the dura for the drainage of the CSF into the venous sinuse
Where does the majority of the venous blood drain to?
Majority drains to the superior sagittal sinus
How does the venous blood leave the skull?
Drains to the confluence of the sinuses
Then to the transverse and sigmoid sinuses to the internal jugular veins
DRAW OUT THE VENOUS DRAINAGE
DRAW OUT THE VENOUS DRAINAGE
What is the pathophysiology of a stroke?
This is where there is an aneurysm of the cerebral arteries
What are common causes of stroke/aneurysm formation?
Atherosclerosis Hypertension Old age Head injury - trauma Arteriovenous malformation
Which cerebral arteries are particular vulnerable to clotting and why?
Lenticulostriate arteries - these come off at right angles
How can stroke to the middle cerebral artery present?
Lateral portion of the brain If this is the dominant hemisphere: Global aphasia Sensorimotor loss on the contralateral face, upper limb, trunk (above the waist) If this is the non-dominant hemisphere: Neglect syndrome
How does a stroke to the anterior cerebral artery present?
Less common
Leads to contralateral sensorimotor loss below the waist
Damage to internal part i.e. corpus callosum - joining the two hemispheres - results in split brain syndrome
Urinary incontinence
Personality defects
How does stroke to the posterior cerebral artery present?
More posterior and deeper damage - temporal lobe damage
Impaired memory
Reading and writing deficits
Contralateral homonymous hemianopsia
Why are strokes to the posterior cerebral artery quite rare?
Because there are so many branches before you get to the PCA
What is a transient ischaemic attack? (TIA)
‘Mini stroke’ - temporary loss of brain function less than thirty minutes
Resolves within 24 hours with no long term side effects
What is the significance of a TIA?
This generally acts as a warning sign for the onset of later heart attack or stroke
What is an extra-axial bleed?
What are the different types?
This is a bleed outside of the brain tissue i.e. in the skull cavity rather than in the brain
Epidural (extradural) haematoma
Subdural haematoma
Subarachnoid haematoma
Describe an epidural/extradural haematoma
This is a bleed between the dura mater and the skull
Rapid bleeding - arterial
70% of cases tends to be the middle meningeal artery to supply the meninges (coming off of the maxillary artery
Generally due to trauma at the side of the skull - at the pterion
How can you recognise an epidural/extradural haematoma from an image?
Will see a massive clot at the side of the skull
This clot will press on the softer brain tissue underneath and result in a mass shift effect and then stops at the suture lines - these are strong and prevent the brain tissue from being compressed any further - clot gives a convex lens appearance
How will an extradural haematoma present?
Often will present with a lucid period immediately after the trauma, this is followed by unconciousness
What is a subdural haematoma? Describe this
What is the cause of this?
This is beneath the dura - between the dura mater and the arachnoid
Tends to be due to veins and so is a slow bleed - may not present for up to two weeks following injury
Spread much wider - can cross the suture lines
Due to tearing of the bridging veins that pierce the dura as a result of high speed acceleration to high speed deceleration or vice versa
How can you recognise a subdural haematoma from an image?
These bleeds appear much more crescent shaped than convex lens shaped
These can cross the suture lines
What is a subarachnoid haematoma?
This is between the arachnoid and the pia mater
Generally due to a burst aneurysm - very fast bleed
