Blood Supply to the Brain

Question 1

Why are strokes so serious

Answer 1

3rd most common cause of death in the UK
Leading cause of disabiltiy => 2/3 of stroke survivors become disabled

Huge mortality and morbidity due to

• occlusion of blood flow by clot
• haemorrhage

Both lead to neuronal death

Question 2

Describe the importance of blood supply in the brain

Answer 2

17% of cardiac output
20% of O2 in the body used in the brain
If blood supply interrupted => rapid loss of consciousness
3mins of interrupted blood supply => irreversible damage

Question 3

What are the 2 arterial routes into the brain

Answer 3

Internal carotids

Vertebral arteries

Question 4

Describe the route of the internal carotids into the brain

Answer 4

Common carotid
Internal carotid
S shaped carotid canal into skull
Emerges lateral to sphenoid body next to optic chiasm

Branches into

• Central artery of retina => supplies retina (end artery)
• Opthalmic artery => supplies eye
• Ant cerebral
• Mid cerebral

Question 5

Describe the route of the vertebral arteries into the brain

Answer 5

Subclavian artery 
L and R vertebral arteries
Transverse cervical foramen 
Foramen magnum
Fuse together into vertebral arteries => basilar arteries
Post cerebral artery

Question 6

What is the function of the transverse foramen in the cervical vertebrae

Answer 6

Ascend up C1-6, allows for safe protective passage of vertebral arteries
Vertebral arteries fuse on ventral pons => basilar artery

Question 7

Where is the Circle of Willis found

Answer 7

Surrounds optic chiasm and pituitary at brain base

Found in the subarachnoid space

Question 8

Name the arteries that come off the Circle of Willis

Answer 8

Ant communicating between ant cerebral

Mid cerebral comes off int carotid

Post communicating between int carotid and basilar

Question 9

Name the arteries that branch off the basilar artery

Answer 9

Post cerebral
Sup cerebellar
Pontine branches
Labyrinthine, supply inner ear
Ant inf cerebellar
Post inf cerebellar branches off vertebral

Question 10

Describe the anatomical structure of the cerebellar arteries

Answer 10

All anastamose with each other to supply cerebellum

Question 11

Describe the areas supplied by the middle cerebral artery

Answer 11

Supplies mainly the LATERAL regions of the cerebrum

• Primary motor (upper limbs and face)
• Primary sensory (upper limbs and face)
• Broca and Wernicke’s speech area in dominant hemisphere
• Part of visual field

Question 12

What can happen when the MCA is occluded

Answer 12

Contralateral paralysis and sensory deficits of lower face and arm

Aphasia if dominant hemisphere affected

Hemianopia of contralateral visual field (affects thalamus visual cortex tract)

Question 13

Describe the areas supplied by the anterior cerebral artery

Answer 13

Supplies mainly the MEDIAL regions of the cerebrum

• Frontal lobe (cognition, behaviour and emotion)
• Primary motor (lower limbs and perineum)
• Primary sensory (lower limbs and perineum)
• Internal capusule

Question 14

What can happen when the ACA is occluded

Answer 14

Contralateral paralysis and sensory deficits of lower limbs and perineum

Cognitive behaviours and emotional problems

Sometimes contralateral face, tongue and upper limb due to inner capsule

Question 15

Describe the areas supplied by the posterior cerebral artery

Answer 15

Supplies mainly the posterior regions of the brain

• Occipital (visuals)
• Temporal (language and memory)
• Thalamus

Question 16

What can happen when the PCA is occluded

Answer 16

Memory affected

Contralateral visual field defects

Hemisensory deficits due to thalamus involvement

Question 17

Describe the overlap in cerebral blood supplies

What can happen in a watershed infarct

Answer 17

ACA and PCA both supply medial rim of the lateral brain surface

• However, they are at the ends of the main arteries
• Affected most by decreased perfusion and BP => Watershed infarct => Stroke

Bilateral weakness of upper and lower proximal limbs
Bilateral visual loss/stupor

Question 18

Name the 3 deep cerebral arteries and where do they arise from

Answer 18

ACA => anterior choroidal artery
MCA => MCA deep branches
PCA => PCA deep branches

Question 19

Where do the deep arteries come off the C of W and what do they supply

What happens when the deep artery of the MCA is occluded

Answer 19

ACA and MCA => internal capsule and basal ganglia
PCA => ventral midbrain

MCA via lenticulostriate arteries

Embolus here => lacunar infarcts in end artery

Question 20

Describe the distribution of the vertebral and basilar arteries
What happens if blood flow is occluded here

Answer 20

Basilar supplies cerebellum and pons
Vertebral supplies medulla

Occlusions
-Instantly fatal => coma due to damage to reticular formation/loss of resp control (damage in resp nuclei)

Cerebellar defects
Cranial nerve defects
Deafness if labyrinthine affected

Infarction of ventral pons => locked in syndrome, loss of all voluntary movements

Question 21

What are the pros and cons of anastamoses

Answer 21

Pros
-If 1 artery occluded, affected region will still have a blood supply

Cons
-If part of C of W wall weakens => berry aneurysm => subarachnoid haemorrhage

Question 22

How would you treat a berry aneurysm

Answer 22

Coiled ball of wire inserted into aneurysm to prevent blood from making it bigger

Question 23

Describe the venous cranial drainage

Answer 23

Intercranial veins in subarachnoid space, flow with cerebral arteries

Pierce arachnoid and meningeal layer => pools into the dural superior sagittal sinus => jugular foramen in post cranial fossa => int jugular

Question 24

Describe how the structure of the superior sagittal sinus is unique

Answer 24

Between the periosteal and meningeal layers of the dura and lined by endothelium
No valves here

Question 25

What can happen in a subdural haemorrhage

Answer 25

Slow accumulation of venous blood between dural layers

Often found in the elderly after a fall

Question 26

Describe the route of dural sinus drainage back into the heart

Answer 26

Sup sagittal sinus => L and R transverse sinus

Inf sagittal sinus => straight sinus => L and R transverse sinus

L and R transverse sinus, cavernous sinus => sigmoid sinus leaves skull via jugular foramen => sup jugular bulb of int jugular => brachiocephalic

Question 27

Describe the pathway of the middle meningeal artery
How would you locate the MMA in the skull
How would the MMA get damaged

Answer 27

Branch of the maxillary artery => foramen spinosum to supply bones of the vault

Pterion directly above MMA, damage here => burst MMA

Question 28

What can happen in an epidural haemorrhage

Answer 28

Arterial high pressure bleed fills epidural space

Must be drained, otherwise brainstem compressed

Question 29

Describe the 3 methods of arterial blood supply to the spinal cord

Answer 29

1 ant spinal artery from superior end of vertebral arteries => fuse to form 1 artery

2 post spinal artery from inferior end of vertebral arteries => no fusion here

Radicular arteries from segmental spinal arteries which branch from aorta in thoracic and lumbar regions and enter via intervertebral foramina

Question 30

Describe the 4 methods of venous drainage from the spinal cord

Answer 30

1 ant spinal vein

2 posteriorlateral spinal veins

1 posterior spinal vein

Radicular ceins

All anastomose in internal vertebral venous plexus