Pathology of Cerebrovascular disease Flashcards
What arteries supply the areas on the diagram?
What arteries supply the brainstem and cerebellum?
Vertebral and basilar arteries
What is the difference between ischaemia and hypoxia?
Ischaemia is the lack of blood flow
Hypoxia is the lack of oxygen
What is a stroke?
Focal neurological deficit (loss of function affecting a specific region of the central nervous system) due to disruption of blood supply
(WHO)
What 3 ways can the blood flow and thus supply of oxygen be interrupted?
Changes in:
- vessel wall
- blood flow (incl. blood pressure)
- blood constituents
Think Virchow’s triad
What changes in the vessel wall can cause interrupt the supply of oxygen?
Abnormality of the physical wall:
- Atheroma
- Vasculitis
Abnormality of outside pressure:
- Strangulation
- Spinal cord compression
- Compression of veins
What can change the blood flow & pressure to interrupt oxygen supply?
decreased blood flow
increased blood pressure bursting vessels
How can abnormal blood constituents lead to interrupted oxygen supply?
Thrombosis of arteries and rarely veins
Bleeding due to anticoagulation, reduced platelets and clotting factors
In practice, what are the 3 main causes of localised interrupted blood supply?
Atheroma & thrombosis:
- Ischaemia
Thromboembolism:
- Ischaemia
Ruptured aneurysm:
- Haemorrhage
What area of the brain most commonly becomes ischaemic due to atheroma & thrombosis?
Why?
An internal carotid artery thrombosis will cause ischaemia in the middle cerebral artery territory
This means parts of the Frontal, temporal and/or parietal lobes could be affected
For how long must symptoms last before a stroke is a stroke?
>24 hours = stroke
<24 = Transient ischaemic attack
If TIA - the transient symptoms are due to reversible ischaemia - tissue is still viable
If stronk - longstanding symptoms mean tissue has infarcted causing localised brain death
Why is infarction permanent in the brain?
Neurones don’t regenerate
What shape/pattern does the infarcted area typically look like in stroke
An outward wedge - showing the normal perfusion territory
What are the labels pointing at in this lovely photo
Infarcted tissue initially goes soft then cystic
What happens in the inflammatory response seen in the previous photo
What process do the cells present contribute to?
There will be lots of foamy macrophages cutting about that are visible histologically
These make up the repair process which leads to gliosis
Gliosis is the CNS equivalent to fibrosis
What is the long term structural changes to the brain after infarction?
The infarcted area jut kinda rots away - leaving a cyst-like cavity
The edges of these cavities have lots of yellow discolouration
Why do some heart arrhythmias cause strokes?
Arrhythmias such as Atrial fibrillation can lead to a thrombosis forming in the atrium, for example, can embolize
They can end up in the carotid arteries and if they go up the ICA then they can occlude vessels such as the MCA
What characteristic of the arteries in the brain allows aneurysms to form relatively easily?
Beyond the carotid & vertebral arteries - the cerebral arteries have quite thin walls
Slight weakening + hypertension can often lead to aneurysms
When an aneurysm ruptures, obviously not much blood flows through the artery distal to the haemorrhage
How does the distal artery react to the rupture?
Distal artery will spasm
This will cause ischaemia distal to the site of haemorrhage
What are the 2 common sites of aneurysm rupture in the brain?
Basal ganglia - microaneurysms form in hypertensive patients
Circle of Willis – Berry aneurysm forms in hypertensive patients
What are some causes of generalised interruption to cerebral blood supply or hypoxia?
Low O2 in blood:
- this would be hypoxia without ischaemia
- Eg - CO2 poisoning, near drowning, Respiratory arrest
Inadequate supply of blood:
- regardless of whether or not blood is oxygenated
- Cardiac arrest, hypotension, brain swelling (trauma)
Rarely - some conditions prevent the usage of oxygen by tissues - eg cyanide poisoning
How can hypotension lead to hypoxia/infarction in the brain?
Perfusion of the central areas of the arteries territories would be perfused okay
Perfusion of Watershedareas (where territories cross) would bepoor - at risk of infarction. Not enough oxygen delivered as these are like the end branches of the arteries tree
What is shown below?
These are watershed infarcts - the typical outcome of pure hypotension with oxygenated blood
Notice that they are symmetrical - ie same area on both sides
If a patient suffers a cardiac arrest and the brain suffers complete loss of blood flow and oxygen - what is the outcome?
Cortical necrosis (infarction)
This is characterised by large areas of grey matter thinning (necrosis) with a laminar appearance (lined)
