27. Blood supply to the brain

Question 1

How do cerebral arteries differ from normal ones?

Answer 1

Thinner walls
Much more easily blocked
Do not have the same amount of elastic and smooth muscle
Look very similar to veins

Question 2

How do cerebral veins differ from normal ones?

Answer 2

Thin walled
No valves present
Look very similar to arteries
Reliant on gravity for the removal of venous blood from the brain

Question 3

Where the blood supply to the anterior part of the brain come from?

Answer 3

Internal carotid arteries - gives way to the middle and anterior cerebral arteries
This is 80% of cerebral blood flow

Question 4

Where does the blood supply to the posterior part of the brain come from?

Answer 4

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

Question 5

DRAW CIRLCE OF WILLIS

Answer 5

DRAW CIRLCE OF WILLIS

Question 6

What is the biggest branch of the internal carotid artery?

Answer 6

The middle cerebral artery

Question 7

What are the lenticulostriate arteries?

Answer 7

These are the arteries that provide the basal ganglia and the internal capsule

Branches of the middle cerebral

Question 8

Where in the brain do the different cerebral arteries supply?

Answer 8

Anterior - medial superior
Middle - Lateral region of the brain
Posterior - medial inferior

Question 9

What foramina do the vertebral arteries pass through and what do they then form?

Answer 9

Vertebral arteries through the foramen magnum then form the basillar artery

Question 10

What part of the brain does the basillar artery supply?

Answer 10

The pons (pontine branches)

Question 11

What part of the brain does the posterior cerebral artery supply?

Answer 11

Midbrain
Thalamus and internal capsule
Inferior and medial aspects of the occipital cortex

Question 12

What are bridging veins?

Answer 12

These are veins which pierce through the dura to allow venous drainage

Question 13

What other structure can pierce the dura and what is their function?

Answer 13

Arachnoid granulations - these pierce the dura for the drainage of the CSF into the venous sinuse

Question 14

Where does the majority of the venous blood drain to?

Answer 14

Majority drains to the superior sagittal sinus

Question 15

How does the venous blood leave the skull?

Answer 15

Drains to the confluence of the sinuses

Then to the transverse and sigmoid sinuses to the internal jugular veins

Question 16

DRAW OUT THE VENOUS DRAINAGE

Answer 16

DRAW OUT THE VENOUS DRAINAGE

Question 17

What is the pathophysiology of a stroke?

Answer 17

This is where there is an aneurysm of the cerebral arteries

Question 18

What are common causes of stroke/aneurysm formation?

Answer 18

Atherosclerosis 
Hypertension 
Old age 
Head injury - trauma 
Arteriovenous malformation

Question 19

Which cerebral arteries are particular vulnerable to clotting and why?

Answer 19

Lenticulostriate arteries - these come off at right angles

Question 20

How can stroke to the middle cerebral artery present?

Answer 20

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

Question 21

How does a stroke to the anterior cerebral artery present?

Answer 21

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

Question 22

How does stroke to the posterior cerebral artery present?

Answer 22

More posterior and deeper damage - temporal lobe damage
Impaired memory
Reading and writing deficits
Contralateral homonymous hemianopsia

Question 23

Why are strokes to the posterior cerebral artery quite rare?

Answer 23

Because there are so many branches before you get to the PCA

Question 24

What is a transient ischaemic attack? (TIA)

Answer 24

‘Mini stroke’ - temporary loss of brain function less than thirty minutes
Resolves within 24 hours with no long term side effects

Question 25

What is the significance of a TIA?

Answer 25

This generally acts as a warning sign for the onset of later heart attack or stroke

Question 26

What is an extra-axial bleed?

What are the different types?

Answer 26

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

Question 27

Describe an epidural/extradural haematoma

Answer 27

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

Question 28

How can you recognise an epidural/extradural haematoma from an image?

Answer 28

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

Question 29

How will an extradural haematoma present?

Answer 29

Often will present with a lucid period immediately after the trauma, this is followed by unconciousness

Question 30

What is a subdural haematoma? Describe this

What is the cause of this?

Answer 30

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

Question 31

How can you recognise a subdural haematoma from an image?

Answer 31

These bleeds appear much more crescent shaped than convex lens shaped

These can cross the suture lines

Question 32

What is a subarachnoid haematoma?

Answer 32

This is between the arachnoid and the pia mater

Generally due to a burst aneurysm - very fast bleed