Pathology of Stroke

Question 1

What main vessels supply the anterior circulation?

Answer 1

2 internal carotid arteries which become:

• anterior cerebral arteries
• middle cerebral arteries

Question 2

What main vessels supply the posterior circulation?

Answer 2

Basilar artery from 2 vertebral arteries (and anterior spinal artery)

Question 3

What factor determines the variation of blood flow between regions?

Answer 3

Metabolic rate of those areas

• which is controlled via varied cerebral arteriolar tone
• thus resistance

Question 4

What is autoregulation of blood flow?

Answer 4

Cerebral blood flow is maintained at same rate over a range of blood pressures
- controlled by a variation of arteriolar control

Question 5

What is the range of blood pressures in which cerebral blood flow can be kept constant?

Answer 5

~ 50 mmHg to 170 mmHg in normal person

Question 6

Describe how chronic hypertension can affect the autoregulation of blood flow?

Answer 6

Can lead to “normal range” being reset to higher level e.g. ~ 80 to 200 mmHg

Can cause problems:

• if below 90, arteriolar system no longer able to compensate and may lead to blackout
• if too high, cerebral blood flow will be maintained, but will lead to cerebral oedema and hypersensitive encephalopathy

Question 7

Why may be the causes of autoregulation failure?

Answer 7

Increasing age

Head trauma

SAH or ischaemic stroke

Cerebral hypoxia

High pCO2

Question 8

What may the failure of autoregulation result in?

Answer 8

Cerebral blood flow varying with high/low BP

Increased stroke risk (esp. iscaemic due to low BP)

Question 9

What CBF level may result in ischaemic damage of tissue?

Answer 9

50% lower than normal range

Question 10

Describe Glial cells

Answer 10

Non-neuronal support cells that maintain homeostasis

They:

• form myelin
• provide support and protection for the brain’s neurones

Metabolise aerobically and anaerobically

Supply lactate to adjacent neurones

Question 11

Describe neurones

Answer 11

Obligate aerobes which are very sensitive to ischaemia

Can metabolise glucose

Mostly aerobically metabolise lactate supplied by glia

Question 12

What is the difference between ischaemia and hypoxia?

Answer 12

Ischaemia - a restriction in blood supply leading to dysfunction +/- damage

Hypoxia - oxygen deprivation

Question 13

What are the main causes of hypoxia?

Answer 13

Low O2 in inspired air

Airway obstruction

Lung disease

Reduced O2 carrying capacity of blood

Ischaemia

Inhibition of aerobic respiraton

Question 14

Describe some of the factors which the effects of hypoxia/ischaemia depend on?

Answer 14

Degree of ischaemia/hypoxia

Duration of ischaemia/hypoxia

Temperature (incr. metabolic rate at higher temp)

Blood glucose (incr. metabolic rate at higher levels)

Question 15

What is global ischaemia?

Answer 15

Result of interruption of circulation => resultant general reduction in cerebral perfusion

Question 16

What are the causes of global ischaemia?

Answer 16

cardiac arrest

severe hypotension

shock

Question 17

What is the effect of global ischaemia?

Answer 17

Selective neuronal necrosis
- neurones more susceptible to ischaemia due to obligate aerobic nature

Cortical laminar necrosis
- definite layers of neurones lost due to increased susceptibility and decreased supply (3rd layer lost most easily)

Watershed infarcts

• occur at watersheds between different arterial supplied
• due to poor blood supply from distal end arteries
• therefore increased susceptibility to ischaemia

Question 18

What are the clinical outcomes of global ischaemia?

Answer 18

Transient confusion
- if ischaemia brief due to obligate aerobic nature

Focal deficits
- if ischaemia only enough to causes infarction in certain areas

Brain death and “non-perfused brain”

• raised intracranial pressure due to oedema
• medulla may escape infarction th. resp functions intact

Question 19

What is the prognosis of stroke?

Answer 19

Of those who survive:

• 50% make good recovery
• 50% permanently disabled

Question 20

Describe artherosclerosis leading to resultant thrombosis

Answer 20

Fatty streaks build up to fibrous/complicated plaques

Vessels stenose and plaques haemorrhage (i.e. blood enters plaque)

Plaques rupture causing thrombosis & sometimes emboli

Question 21

Why does vasculitis (result in thrombosis) occur?

Answer 21

Due to infection

Collagen/vascular disease

Granulomas

Question 22

Where do intracerebral haemorrhages most commonly occur?

Answer 22

Thalamus / basal ganglia

Question 23

Why do intracerebral haemorrhages most commonly occur?

Answer 23

Arteriosclerosis/aneurysms of small diameter arterioles cause them to rupture

Question 24

What is the most common cause for sub-arachnoid haemorrhage?

Answer 24

Rupture of Saccular (Berry) Aneurysm
- most commonly occur in anterior circle of willis

note: almost always a result of congenital abnormality