Pathology of Cerebral-Vascular Disease Flashcards
Define ischaemia
Lack of blood flow
Define hypoxia
Lack of oxygen
What is the WHO definition of 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 basic cause of a stroke?
Interruption of supply of oxygen and nutrients, causing damage to brain tissue
What are three factors that interrupt the supply of oxygen?
Virchows Triad - changes in:
• Vessel wall
• Blood flow (including blood pressure)
• Blood constituents
Give examples of what changes that occur in the vessel wall?
- Abnormality of wall - atheroma
* Outside pressure - i.e. compression of spinal cord or veins, strangulation
Give examples of what changes occur to blood flow and pressure
- Decreased - when a person is in shock (loss of blood)
* Increased pressure which can burst vessels
Give examples of what changes occur to blood constituents
- Thrombosis or arteries and rarely veins
* Bleeding due to anticoagulation, reduced platelets and clotting factors
What are the three main causes of LOCALISED interrupted blood supply?
- Atheroma + thrombosis of artery causing ischaemia
- Thromboembolism (i.e. from LA) causing ischameia
- Ruptured aneurysms of a cerebral vessel causing haemorrhage
Where is a common place for an atheroma to form?
Bifurcation of common carotid artery
How does an atheroma of the carotid sinus lead to stroke?
Thrombosis form by build of of platelets and fibrin, and if this dislodges and travels up ICA, it will travel into the middle cerebral artery and cause ischaemia in MCA territory
Describe the importance of the duration of ischaemia
- 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
Describe the pathogenesis of an ischaemic stroke
Brain is very sensitive to O2 ischaemia, and a few minuted of hypoxia or anoxia will cause it.
This can lead to infarction, which causes damage to neurones (permanent). Neurones do not regenerate.
Why does ischaemia not immediately arise if the carotid arteries are fully occluded?
Due to vertebral arteries still supplying circle of willis (only for 3mins)
What is a regional cerebral infarct?
A localised area of brain death reflecting arterial perfusion territory
Classically wedge-shaped, which starts soft and then becomes cystic.
What is gliosis?
CNS equivalent of fibrosis - yellow colouration at edge of infarcted area caused by foamy macrophages
Describe the change in histology after infarction?
- Loss of neurones
* Foamy macrophages - repair process leading to gliosis
What do old infarct cause?
Loss of brain tissue, cystic spaces and gliosis
Why is the location of ischaemia important?
Small affected area of one part of brain may not cause too much impairment, but a similar size of affected area in another part of brain may be devastating
Describe how a thromboembolism can lead to infarction
Heart with atrial fibrillation can cause thrombosis of atrial appendages.
If it dislodges it will embolism to aorta and possibly carotid (or any other) arteries - but L common carotid is inline with ascending aorta.
Travels to MCA and occludes it.
Describe how a ruptured vessel wall can lead to haemorrhage stroke
The cerebral arteries are thin walled, therefore hypertension causing the waking of the wall and formation of an aneurysm
Decreased blood blood flow vitally to brain due to spams of artery
Why are cerebral arteries thin walled?
As your brain does not want to be affected by substances, like caffeine, to ensure constant blood flow
What does rupturing of a vessel cause?
Haemorrhage (+/- distal ischaemia due to spasm of artery)
Whereas other two cause ischaemia
Name two common sites of ruptures vessels causing haemorrhage stroke
- Basal gangli - microaneurysms form in hypertensive patients
- Circle of Willis - Berry aneurysm forms in hypertensive patient
Name causes of GENERALISED interruption of blood supply
- Low O2 in blood (hypoxia with intact circulation
- Inadequate supply of blood (flow of blood not occuring)
• Rarely: Inabiloty to use O2 - i.e. cyanide poisoning
What are three causes of hypoxia?
CO2 poisoning, drowning, respiratory arrest
What are three causes of inadequate blood supply and/or hypoxia?
- Hypotension
- Cardiac arrest
- Complex case
What is the effect of hypotension on perfusion of the brain?
It causes the central part of the artery territory to be perfused, but the edges in-between each territory (the watershed zones) are poorly perfused
This causes watershed infarcts (distinct zones between territories)
How does a cardiac arrest cause infarction?
No circulation to brain and no oxygen in blood – all of brain deprived of blood flow and O2
What is the effect of cardiac arrest on perfusion of the brain?
Causes large areas of grey matter thinning and necrosis –> cortical necrosis
Complex case effect of perfusion:
75yr old 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 has happened?
Reperfusion with good circulation after cardiac arrest (no O2 or perfusion) comes with complication.
Combination of poor perfusion and atheroma in carotid arteries cause regional infarcts;
• Watershed infarcts
• Laminar cortical necrosis
• Region infarcted related to poor flow through cerebral vessels narrowed by atheroma
