Stroke Flashcards
(12 cards)
What is stroke?
Neurological deficit attributed to an acute focal injury of the central nervous system by a vascular cause, result of ischaemia meaning insufficient tissue perfusion.
~10% of deaths in the UK and one of the leading causes of deaths in developed countries
What are the two types of stroke and their subtypes
Ischaemic (85%): Large vessel stroke -> ischaemic penumbra, small vessel stroke and transient ischaemic attacks
Haemorrhagic (15%): spontaneous intracerebral haemorrhage, burst aneurysm, subarachnoid haemorrhage,
What are the differences between ischaemic and haemorrhagic stroke?
Ischaemic strokes have a ~12% fatal rate within one month, whereas haemorrhagic strokes have ~30% fatality within 1 month, which is even higher in less developed countries
Ischaemic strokes are caused by reduced blood flow to a particular part of the brain, such as by the occlusion of a cerebral artery. However, haemorrhagic strokes are due to a ruptured blood vessel and are commonly associated with high BP and diseases which weaken arterial walls
In comparison to ischaemic strokes, haemorrhagic strokes severity is not dependent on type of stroke.
What are the differences between large vessel strokes, small vessel strokes, and transient ischaemic attacks?
In large vessel strokes cerebral blood vessels are occluded by an embolus which is usually a small blood clot which often originate from the heart. However, in-situ thrombosis can also occur. The larger the blood vessel the greater the damage that occurs due to the larger territory supplied.
Small vessel strokes occur due to arteriosclerosis of arteries (hardening). This means that they are unable to dilate in response to blood flow leading to a lacunar infarct. Leads to a small area of tissue damage that can often occur in the basal ganglia or internal capsule.
Transient ischaemic attacks involve a brief period of cerebral ischaemia which may be reversible. Symptoms usually resolve in minutes and do not last longer than 24 hours. Permanent damage only occurs in 10-20% of cases. Associated with increased risk for stroke or heart attack.
What is the ischaemic penumbra?
Within the first hour of stroke a necrotic core lesion is established in which the blood flow is below 20%
The area surrounding the legion is the ischaemic penumbra where blood follow is marginally better (20-40%)
Neurons in this region may remain viable for up to 24 hours and can be potentially salvaged.
What are the differences between haemorrhagic stroke types.
Spontaneous intracerbreal strokes can occur in cerebral lobes (10-20%), basal ganglia (50%), thalamus (15%), brain stem (10-20%) and cerebellum (10%).
Burst aneurysm are caused by the weakening of an artery wall which leads to a bulge or balloon of a vessel. Due to this weak nature they sometimes burst. 1/3 of haemorrhagic strokes caused by aneurysm.
Subarachnoid haemorrhages often occur with head trauma. Account for 5% of all strokes. They do not necessarily cause a focal neurological deficit. Often present with a severe headache and are caused by berry aneurysms which are a medical emergency with a high mortality rate.
What damage is likely to occur due to haemorrhagic strokes?
1st injury due to compression by haematoma and increase in intracranial pressure.
2nd injury is contributed by inflammation, disruption of blood-brain barrier, oedema, overproduction of free radicals and release of haemoglobin and iron from the clot. Much more destructive than ischaemic stroke.
Why do strokes occur in different areas of the brain
Ischaemic strokes more likely to occur anteriorly as this is where the internal carotid artery divies into the middle cerebral artery and anterior cerebral artery. As from carotid artery, cardiogenic emboli are more likely to enter MCA and ACA.
The brain also has posterior circulation, the basilar artery ascends along the basal pons to reach the midbrain and sp;its. Vessels then wind around the midbrain and pass posteriorly.
Basal ganglia has good blood supply from the MCA and thalamus also receives from similar penentrating arteries.
What are the 4 classifications of stroke?
Total anterior circulation syndrome (TACS)
Partial anterior circulation syndrome (PACS)
Posterior circulation syndrome (POCS)
Lacunar syndrome (LACS)
How can stroke be treated at the acute stages?
Clot busting drugs -> thrombolysis which needs to be delivered within 4.5 hours
Mechanical treatment -> thrombectomy which is only effective in treating ischaemic strokes caused by a blood clot in a large artery int he brain
Why do consequences of stroke often involve motor systems?
All stroke syndromes tend to involve an impacted motor system as large parts of both the subcortical and cortical areas are involved in control of movement. Most important tract in humans for precise control of limbs is the corticospinal tract as make direct contact with alpha motor neurons in the spine. Damage to the neurons at the origin of the tract or tract itself can have devastating consequences.
What does stroke inform about organisation of the brain?
Strokes revealed specific symptoms, for example, ‘Tan’ who could only produce the word ‘Tan’ after having a stroke in the left frontal lobe. This led to the discovery of Broca’s area being the location of the brain responsible for producing speech. Broca’s aphasia results from damage to this area leading to effortful speech where patients can understand words but find it difficult to produce them.
In contrast, damage to Wernicke’s area in contrast leads to fluent aphasia, which involves poor comprehension. Patients are still able to produce effortless speech but there is reduced meaning.
Through these strokes able to determine that language is localised to the L hemisphere and that speech production and language understanding are lateralised and produced in different areas showing that small lesions can have large consequences.
