Blood supply to the CNS

Question 1

What percentage of cardiac output goes to the brain?

Answer 1

10-20%

Question 2

What percentage of liver glucose does the brain use?

Answer 2

66%

Question 3

State the two main sources of blood supply to the brain?

Answer 3

Vertebral arteries (posteriorly)

Internal carotid arteries (anteriorly)

Question 4

State the major artery that the vertebral arteries branch off and describe the path of the vertebral arteries to the brain.

Answer 4

1st branch of the subclavian artery.
It travels superiorly to enter the transverse foramina of C6 to C1 vertebrae. It then travels through the foramen magnum to enter the cranial cavity.

Question 5

Where do the right and left vertebral arteries anastomose and name the resultant artery?

Answer 5

At the midline, at the level of the external acoustic meatus, anterior to the medulla oblongata.
Basilar artery

Question 6

Describe the circle of Willis

Answer 6

Loop of arteries found along base of brain

Anterior side = anterior communicating artery

Two anterolateral sides = proximal end of anterior cerebral arteries (anterior branches of internal carotid)

Two posterolateral sides = posterior communicating arteries (posterior branches of internal carotid)

Posterior sides = proximal end of posterior cerebral arteries (branches of the basilar artery)

(Note that the middle cerebral artery also branches off the internal carotid in the same place as the other two)

Question 7

Define Stroke

Answer 7

A rapidly developing focal disturbance of brain function of presumed vascular origin that lasts more than 24 hours

Question 8

Define Transient Ischaemic Attack (TIA)

Answer 8

A rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours

Question 9

What percentage of strokes are caused by infarction and what percentage are caused by haemorrhage?

Answer 9

85% infarction

15% haemorrhage

Question 10

Define Infarction

Answer 10

Degenerative changes which occur in tissue following occlusion of an artery

Question 11

Define Cerebral ischaemia

Answer 11

Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly (not just due to hypoxia/anoxia)

Question 12

State two causes of occlusion

Answer 12

Thrombosis

Embolism (e.g. thrombi from the heart or atherosclerotic debris from the internal carotid)

Question 13

Summarise the epidemiology of stroke

Answer 13

3rd commonest cause of death

100,000 deaths in UK per annum

50% of survivors are permanently disabled

70% show an obvious neurological deficit

Question 14

List the main risk factors for stroke

Answer 14

Age
Hypertension
Cardiac disease
Smoking
Diabetes mellitus

Question 15

Describe the perfusion fields of the brain.

Answer 15

Anterior cerebral artery - supplies the medial part of both hemispheres (until parieto-occipital sulcus)

Middle cerebral artery - supplies most of the lateral part of the hemisphere

Posterior cerebral artery - medial and lateral parts of the posterior part of the hemisphere

Question 16

Describe the features of a disturbance in the anterior cerebral artery

Answer 16

• Paralysis of contralateral leg > arm, face
• Disturbance of intellect, executive function and judgement (abulia)
• Loss of appropriate social behaviour

Question 17

Describe the features of a disturbance in the middle cerebral artery

Answer 17

“Classic stroke”

• Contralateral hemiplegia (arm > leg)
• Contralateral hemisensory deficits
• Hemianopia
• Aphasia (Left sided lesion)

Question 18

Describe the features of a disturbance in the posterior cerebral artery

Answer 18

Visual deficits - homonymous hemianopia, visual agnosia

Question 19

Which parts of the brain are involved in speech and understanding language?

Answer 19

Broca’s area - speech

Wernicke’s area - understanding language

Question 20

What are lacunar infarcts?

Answer 20

Small spaces (lacunae) that appear in the brain due to small vessel occlusion 
The clinical deficit is dependent on the location of the small vessel occlusion 
Can be caused by hypertension

Question 21

Classify the four types of haemorrhage stroke

Answer 21

Extradural - caused by trauma => immediate effects

Subdural - caused by trauma => delayed effects

Subarachnoid - caused by ruptured aneurysms

Intracerebral - caused by spontaneous hyper-tensive rupture of small vessels

Question 22

Why are extradural haemorrhages more rapid onset than subdural haemorrhages?

Answer 22

Extradural haemorrhages are caused by rupture of a meningeal ARTERY (high pressure) whereas subdural haemorrhages are caused by rupture of veins in the skull. The middle meningeal artery runs adjacent to the pterion (weakest part if skull; where bones meet in the temple area)

Question 23

Outline the different types of herniation caused by haemorrhage

Answer 23

Subfalcine: the cingulate cortex herniates below the fall
Uncal: the medial temporal lobe (uncus) herniates below the tentorium
Tonsillar: the cerebellar tonsils herniate through the foramen magnum