Stroke

Question 1

What is a stroke?

Answer 1

Interruption of blood flow to a part of the brain causing ischaemia due to blockage of an artery or haemorrhage

Question 2

What are the types of stroke?

Answer 2

Ischaemic stroke (thrombotic and embolic) and haemorrhagic (parenchymal and subarachnoid)

Question 3

What is a transient ischaemic attack (TIA)?

Answer 3

This involves a focal neurological deficit with clinical symptoms that always last less than 24 hours where the ischaemia is confined to an area of the brain or eye that is perfused by a specific artery.

Question 4

What is thought to be the cause of a TIA?

Answer 4

They are thought to result from the release of a small embolus from a thrombus which causes the temporary blockage of a downstream vessel, but this quickly dissolves and the area becomes re-perfused.

Question 5

What is the most common type of stroke?

Answer 5

Ischaemic stroke (85%)

Question 6

Describe thrombotic stroke

Answer 6

This is a form of ischaemic stroke which involves the development of a blood clot in a cerebral vessel caused by atherosclerosis

Question 7

When does thrombotic stroke usually occur and why?

Answer 7

During sleep; this is because during sleep there is reduced sympathetic innervation and therefore blood pressure is lower. This decrease in blood pressure means that there is less pressure to force through the lumen of an occluded artery, and therefore the lumen may entirely close and occlude any flow.

Question 8

Describe embolic stroke

Answer 8

This is a form of ischaemic stroke that occurs due to fragments of blood clots or clumps of bacteria leading to occlusion of a blood vessel.

Question 9

What is the likely cause of embolic stroke?

Answer 9

Ordinarily the clot has migrated from the left side of the heart, and therefore heart conditions that lead to blood pooling predispose this condition e.g. MI, atrial fibrillation and defective heart valves

Question 10

What is a lacunar stroke?

Answer 10

A type of ischemic stroke that occurs when blood flow to one of the small arteries deep within the brain becomes blocked

Question 11

What are the symptoms of stroke?

Answer 11

• Sudden numbness or weakness of face, arm or leg, especially if it’s unilateral
• Sudden confusion, difficulty understanding or speaking
• Sudden trouble seeing in one or both eyes
• Sudden trouble walking, dizziness, loss of balance or coordination
• Sudden severe headache with no known cause

Question 12

What is the role of the internal capsule in the cerebrum?

Answer 12

It carries all of the motor commands from the motor cortex to the brainstem and spinal cord

Question 13

Which artery is often implicated in strokes?

Answer 13

Middle cerebral artery, particularly at the junction where it forms the lenticulo-striate arteries as these leave at an acute angle (90 degrees) and therefore predisposes emboli blockage here.

Question 14

What are the lenticulo-striate arteries and what is their clinical significance?

Answer 14

These are branches from the middle cerebral artery which can often become occluded in store and they act to supply the basal ganglia and the internal capsule and therefore are associated with the production of many of the general symptoms of stroke.

Question 15

Explain the importance of the sodium pump in neurones (especially in the cerebrum)

Answer 15

Involved in maintaining membrane potential but also the removal of sodium from the nerve channel means water leaves by osmosis to prevent cellular swelling. Therefore if there is ischaemia then these pumps won’t be able to obtain ATP to facilitate this, and therefore the sodium will remain intracellularly and lead to neuronal swelling. This can also lead to compression of structures in the interstitium such as the cerebral veins, and this can worsen the hypoxia.

Question 16

How may stroke lead to neurotransmitter accumulation (excitotoxicity)?

Answer 16

As there is no ATP available due to hypoxia, the glial cells can’t facilitate potassium uptake and therefore extracellular potassium remains elevated and continues to stimulate the depolarisation of the neurones in the brain to secrete glutamate in an excitatory response. This leads to excess activation of NMDA and AMPA (glutamate) receptors in the brain; excess stimulation of NMDA leads to excess influx of calcium into nerve cells –> rapid excitotoxicity and excess stimulation of AMPA receptors leads to slow/delayed excitotoxicity

Question 17

What is the main excitatory neurotransmitter in the brain?

Answer 17

Glutamate

Question 18

What is meant by the excitotoxic loop?

Answer 18

The increased glutamate secretion due to high extracellular potassium levels leads to activation of NMDA and AMPA glutamate receptors which causes calcium influx into the post-synaptic neurone which increases the metabolic demand of the neurone, and therefore more oxygen is needed, but there is already an absence of oxygen and therefore this leads to the formation of reactive oxygen species (free radicals) due to seeking out other non-aerobic metabolic pathways and this can trigger cell death.

Question 19

What is tonsillar herniation?

Answer 19

If there is a severe rise in the intracranial pressure, this can cause the cerebellum to push through the foramen magnum and cause compression of the lower brainstem and upper cervical spinal cord; this leads to intractable headache, head tilt, neck stiffness and an individual’s level of consciousness may decrease or give rise to flaccid paralysis.

Question 20

Define ‘penumbra’

Answer 20

The area surrounding an ischaemic event

Question 21

Outline the three regions of brain that surround a stroke focus

Answer 21

There are three regions of brain that surround a stroke focus:

1. Inevitable death region (closest to stroke focus point)
2. The penumbra region where neurones are hypoxic and/or damage but may survive
3. Cell survival zone

Question 22

Outline the goals of stroke treatment

Answer 22

The main goal of current stroke treatment is to maximise the survival of neurones in the penumbra region by restoring blood flow, combating excitotoxicity and combatting free radical damage

Question 23

How is blood flow restored in the treatment of stroke?

Answer 23

Tissue plasminogen activators are administered to aid in the breakdown of the clot to allow reperfusion

Question 24

How is excitotoxicity resolved in the treatment of stroke?

Answer 24

a. NMDA antagonists – these block the NMDA receptors on the post-synaptic cells and therefore also block fast excitotoxicity
b. AMP antagonists – these slow down the slow excitotoxicity process
c. Drugs to prevent delayed triggering of apoptotic pathways

Question 25

How is free radical damage/production combatted in the treatment of stroke?

Answer 25

a. Antioxidants – vitamin C and E may be given intravenously to boost the brain’s antioxidant defences
b. Free radical scavenging enzymes – this includes superoxide dismutase

Question 26

How may strokes be prevented?

Answer 26

Treat hypertensioon, treat atrial fibrillation and prescribe statins

Question 27

Which brain cells are involved in the re-uptake of potassium?

Answer 27

Glial cells using ATP