Acute ischaemic stroke (AIS) specifically refers to an episode of neurological dysfunction caused by focal cerebral infarction (REF).
It differs from haemorrhagic strokes:
AIS implies arterial thrombosis and is differentiated here from cerebral venous thrombosis, which has different presentation, investigations and management.
EPIDEMIOLOGY
14 million strokes per year globally.
2nd leading cause of death worldwide
1 in 4 people globally will have a stroke.
CLINICALLY RELEVANT ANATOMY
The brain is supplied by the
- Left and right internal carotid arteries
- Left and right vertebral arteries
These arteries unite within the skull (through communicating arteries) creating the “Circle of Willis”, supplying much of the brain.
For those needing a 2 minute refresher on the blood supply to the brain please watch the following video as it will held understand some of the finer points to come.
Otherwise keep moving along to the CT angiograms below!
Insert GIFs of CTs showing each vascular territory
Touch the different vessels on this circle of Willis to see what’s what in this CT Angiogram
Scroll through this spin around the cerebral vessels to appreciate how it works in 3 dimensions
TIME IS BRAIN
CLINICALLY RELEVANT PATHOPHYSIOLOGY
> The brain needs about 50 ml/100 g/min blood flow with an oxygen metabolic rate of 3.5 cc/100 g/min.
> Blood flow < 10 ml/100 g/min: neuronal function severely affected
> Blood flow < 5 ml/100 g/min: neurons unable to survive
Generally, there is some alteration in brain metabolism if blood flow is interrupted for 30 seconds.
In ischaemic stroke, disruption of blood flows to the brain for a few minutes causes hypoxia and hypoglycemia, which leads to infarction of brain tissues.
A vicious cycle (ischaemic cascade) ensues due to accumulation of sodium, calcium, and water in the injured brain cells, which lead to release of excitatory neurotransmitters causing further cell injury.
More detail on stroke pathophysiology if you’re interested….
Pathophysiology and Treatment of Stroke: Present Status and Future Perspectives