Pathology of Stroke Flashcards
(24 cards)
What main vessels supply the anterior circulation?
2 internal carotid arteries which become:
- anterior cerebral arteries
- middle cerebral arteries
What main vessels supply the posterior circulation?
Basilar artery from 2 vertebral arteries (and anterior spinal artery)
What factor determines the variation of blood flow between regions?
Metabolic rate of those areas
- which is controlled via varied cerebral arteriolar tone
- thus resistance
What is autoregulation of blood flow?
Cerebral blood flow is maintained at same rate over a range of blood pressures
- controlled by a variation of arteriolar control
What is the range of blood pressures in which cerebral blood flow can be kept constant?
~ 50 mmHg to 170 mmHg in normal person
Describe how chronic hypertension can affect the autoregulation of blood flow?
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
Why may be the causes of autoregulation failure?
Increasing age
Head trauma
SAH or ischaemic stroke
Cerebral hypoxia
High pCO2
What may the failure of autoregulation result in?
Cerebral blood flow varying with high/low BP
Increased stroke risk (esp. iscaemic due to low BP)
What CBF level may result in ischaemic damage of tissue?
50% lower than normal range
Describe Glial cells
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
Describe neurones
Obligate aerobes which are very sensitive to ischaemia
Can metabolise glucose
Mostly aerobically metabolise lactate supplied by glia
What is the difference between ischaemia and hypoxia?
Ischaemia - a restriction in blood supply leading to dysfunction +/- damage
Hypoxia - oxygen deprivation
What are the main causes of hypoxia?
Low O2 in inspired air
Airway obstruction
Lung disease
Reduced O2 carrying capacity of blood
Ischaemia
Inhibition of aerobic respiraton
Describe some of the factors which the effects of hypoxia/ischaemia depend on?
Degree of ischaemia/hypoxia
Duration of ischaemia/hypoxia
Temperature (incr. metabolic rate at higher temp)
Blood glucose (incr. metabolic rate at higher levels)
What is global ischaemia?
Result of interruption of circulation => resultant general reduction in cerebral perfusion
What are the causes of global ischaemia?
cardiac arrest
severe hypotension
shock
What is the effect of global ischaemia?
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
What are the clinical outcomes of global ischaemia?
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
What is the prognosis of stroke?
Of those who survive:
- 50% make good recovery
- 50% permanently disabled
Describe artherosclerosis leading to resultant thrombosis
Fatty streaks build up to fibrous/complicated plaques
Vessels stenose and plaques haemorrhage (i.e. blood enters plaque)
Plaques rupture causing thrombosis & sometimes emboli
Why does vasculitis (result in thrombosis) occur?
Due to infection
Collagen/vascular disease
Granulomas
Where do intracerebral haemorrhages most commonly occur?
Thalamus / basal ganglia
Why do intracerebral haemorrhages most commonly occur?
Arteriosclerosis/aneurysms of small diameter arterioles cause them to rupture
What is the most common cause for sub-arachnoid haemorrhage?
Rupture of Saccular (Berry) Aneurysm
- most commonly occur in anterior circle of willis
note: almost always a result of congenital abnormality
