Pathology of Cerebrovascular Disease Flashcards
A
anterior cerebral artery
B
middle cerebral artery
C
posterior cerebral artery
Describe the venous drainage of the brain
- Veins do not accompany arteries
- Large venous sinuses within dura
A
superior sagittal sinus
B
transverse sinus
C
jugular vein
What is Ischaemia?
lack of blood flow
What is hypoxia?
lack of oxygen
What is anoxia?
no oxygen what so ever
What does ischemia lead to?
hypoxia
Wha does a lack of blood flow cause?
lack of oxygen
WHat are the 2 different main ways a stroke could be caused?
- Focal or localised interrupted blood supply or hypoxia
- Generalised problem with blood supply or hypoxia
What is WHO definition of a stroke?
Focal neurological deficit (loss of function affecting a specific region of the central nervous system) due to disruption of blood supply
What is the cause of a stroke?
Interruption of supply of oxygen and nutrients, causing damage to brain tissue
Many causes of interruption of supply of oxygen
Interruption of supply of oxygen caused by what changes?
- Vessel wall
- Blood flow (including blood pressure)
- Blood constituents
(virchows triad)
What is an example of a change in the vessel wall leading to interruption of supply of oxygen?
abnormality of wall eg atheroma or vasculitis, outside pressure (eg strangulation, spinal cord compression, compression of veins)
What is an example of a change in blood flow and pressure leading to interruption of supply of oxygen?
decreased blood flow, increased blood pressure bursting vessels
What is an example of a change in blood constituents leading to interruption of supply of oxygen?
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 leading to a stroke?
- Atheroma + thrombosis of artery causing ischaemia
- Thromboembolism (for example, from left atrium) causing ischaemia
- Ruptured aneurysm of a cerebral vessel causing haemorrhage
What is a common area for a thromboembolism to form?
left atrium is a very common site, blocks an artery and causes distal ischemia
How can a atheroma cause a stroke?
Where is a common site for it to occur?
Narrowing (for example, atheroma) + thrombosis of artery
Can happen anywhere form the left ventricle upwards to vessels in their brain themselves
Common is the bifurcation of the carotid artery - often get a patch of atheroma as there is turbulent flow
Can the brain go long without oxygen?
no aorund 3 minutes so much shorter than bone or muscle
Where would an internal carotid artery thrombosis typically effetc in the brain?
typically get ischaemia in middle cerebral artery territory
What are the 2 different kind of symtpoms ischemia (a relative lack of blood supply in a tissue or organ) can cause?
Transient symptoms (<24 hours) – due to reversible ischaemia (transient ischaemic attack) = tissue still viable
Longstanding symptoms (>24 hours) – due to irreversible ischaemia causing localised brain death = infarct
Is the brain sensitive to oxygen ischaemia?
Brain is very sensitive to oxygen ischaemia
A few minutes hypoxia or anoxia will cause brain ischaemia
What does ischaemia lead to? and do neurones regenerate?
Can lead to infarction
If infarction then damage to neurones is permanent
Neurones do not regenerate
What is a localised area of brain death
Regional cerebral infarct
What shape is an infarct commonly?
Classically wedge-shape reflecting arterial perfusion territory
What is the texture of a infarct?
Soft and then becomes cystic
What histological changes happen when there is a brain infarct?
Loss of neurones - causes clinical functional deficit
Foamy macrophages –repair process leading to gliosis
Gliosis is CNS equivalent of fibrosis
What is gliosis?
Foamy macrophages repair process leads to gliosis
Gliosis is CNS equivalent of fibrosis
Eventually: old infarct with loss of brain tissue
Is the location of ischaemia very important?
YES
Small affected area of one part of brain may not cause too much impairment
Similar size of affected area in another part of brain may be devastating
If tiny stoke in the brain stem then it can kill you as lots of things are going through the brainstem
How does a thromboembolism form in the left atrium?
AF is the classic arrhythmia which causes stagnant blood to turn into a thrombosis
Any heart disease can cause arrhythmias so any heart disease can cause thrombosis
Heart is set up in humans to supply the brain
What is a common site for a thromboembolism form the brain to travel to?
the middle cereblar artery
What do thromboembolisms cause?
So thromboembolism causes an ischaemic stroke, similar to atheroma/thrombosis
What are the walls of the cerebral arteries like?
Beyond carotids and vertebral arteries the cerebral arteries have thin walls
thin walls and almost no smooth muscles (little) in them
What do the thin walls of the cerebral arteries make them susceptible to?
Weakening of wall + hypertension causes aneurysm to form
Don’t want cerebral vessels in spasm as they have thin walls and almost no smooth muscles (little) in them so makes them weaker and more susceptible to aneurysms
Wall can rupture and hemorrhage comes out of it
What can make cerebral arteries rupture easily?
Wall can then rupture, especially if severe hypertension
What do ruptured vessel walls cause?
Ruptured vessel wall causes haemorrhage and distal ischaemia
What are 2 common sites of ruptured vessels causing haemorrhagic stroke?
- Basal ganglia – microaneurysms form in hypertensive patients
- Circle of Willis – Berry aneurysm forms in hypertensive patient
Why may a haemorrhagic stroke in basal ganglia cause problems?
Internal capsule on the left takes all neuron output form one side so an infarct here would cause lots of problems
Extremely devastating thing to have
Haemorrhagic stroke due to bursting of Berry aneurysm affecting circle of Willis
(pictures)
Review: In practice what are the 3 main causes of localised interrupted blood supply?
And what can be done to prevent them?
- Atheroma + thrombosis of artery causing ischaemia - modify lifestyle, e.g. stop smoking
- Thromboembolism (for example, from left atrium) causing ischaemia - anticoagulants
- Ruptured aneurysm of a cerebral vessel causing haemorrhage - treat hypertension
Now moving onto generalised (rather than localised) problem with blood supply or hypoxia!!
What may cause generalised interrupted blood supply or hypoxia?
- Low O2 in blood (hypoxia with intact circulation of blood)
- Inadequate supply of blood (flow of blood not occurring) – blood may be oxygenated or not
3. Rarely: Inability to use O2 – eg cyanide poisoning
What may be the cause of low O2 in blood (hypoxia with intact circulation of blood)?
C02 poisoning, near drowning, respiratory arrest
What may be the cause of inadequate supply of blood (flow of blood not occurring)?
cardiac arrest, hypotension, brain swelling (eg trauma) - If brain damaged and swells it cuts off its own blood supply as enclosed in hard shell of the skull
A patient has coronary artery bypass with prolonged period of hypotension during operation – patient kept oxygenated by ventilation
Central part of arteries territories are perfused ok
So patient has prolonged period of poor perfusion pressure of brain, but blood is oxygenated
What does this all lead to?
Watershed zones are poorly perfused
Zonal pattern of ischaemia and infarction at interface of territories - leading to death
What are ‘watershed’ infarcts?
Zones of infarction at interface of artery perfusion territores are called ‘Watershed’ infarcts
Zonal pattern of ischaemia and infarction at interface of territories
Pure hypotension with oxygenated blood - watershed infarcts
Usually affects both sides
60 year old male suffers myocardial infarct
Cardiac arrest followed several minutes later by resuscitation
During those minutes – no circulation to brain and no oxygen in blood – all of brain deprived of blood flow and O2
What happens next?
patient dies
Large areas of grey matter thinning and necrosis
Laminar = lines of necrosis and thinning
So complete loss of perfusion and oxygen - cortical necrosis (infarction)
75 year old woman with known coronary artery disease
Suffers bout of pneumonia
Periods of poor oxygenation but adequate circulation (due to pneumonia)
Then suffers cardiac arrest – period of no perfusion and no oxygen
Successful resuscitation then further arrest then dies
What would an autopsy show?
Various types of infarcts
Mixture of different kinds all happening because of previous disease and because of complete loss of perfusion
So in practice many cases are complex and areas of ischaemia and infarction in brain may be very variable
In practice what are 3 main causes of localised interrupted blood supply?
- Atheroma + thrombosis of artery causing ischaemia
- Thromboembolism (for example, from left atrium) causing ischaemia
- Ruptured aneurysm of a cerebral vessel causing haemorrhage
What are 3 examples of brain injury caused by generalised interrupted blood supply
Hypotension - watershed infarction
Cardiac arrest - cortical infarction
Complex case - complex pattern
This lecture will emphasize the importance of ________ versus _________ interruption of blood supply
This lecture will emphasize the importance of localised versus generalised interruption of blood supply
