Stroke: Clinical Overview

Question 1

Describe the risk factors for stroke

Answer 1

Modifiable Risk Factors

• Hypertension: Managing BP through lifestyle changes and medication can reduce risk (Alloubani et al., 2018).
• Smoking: Tobacco promotes the formation of clots and atherosclerosis and reduces the amount of oxygen in the blood (Hill et al., 2017).
• Diabetes: Poorly controlled diabetes accelerates atherosclerosis and increases the risk of ischemic stroke. Managing blood sugar through diet, exercise and medication can mitigate risks (Johansson et al., 2021; Alloubani et al., 2018)
• Dyslipidemia: High levels of LDL and low levels of HDL cholesterol can contribute to the build-up of plagues in arteries, leading to atherosclerosis (Johansson et al., 2021; Hill et al., 2017).
• Obesity: Excess body weight is associated with high BP, elevated cholesterol and diabetes, which all increase risk (Hill et al., 2017).
• Physical Inactivity: Regular physical activity reduces hypertension, obesity and diabetes (Hill et al., 2017 ; Johansson et al., 2021).
• Diet: A diet high in saturated fats, trans fats and cholesterol can raise blood cholesterol levels, while a diet high in sodium can contribute to increased BP. Diets rich in fruits, vegetables and whole grains lower the risk of stroke (Hill et al., 2017; Johansson et al., 2021).
• Alcohol Use: Heavy alcohol consumption increases the risk of hypertension and strokes (ischemic and haemorrhagic) (Hill et al., 2017; Johansson et al., 2021)

Non-Modifiable Risk Factors

• Age: HR per year = 1.08, 95% CI 1.07-1.08 (Johansson et al., 2021)
• Gender: Men have a higher risk than women, HR = 1.41, 95% CI 1.29-1.54 (Johansson et al., 2021)
• Ethnicity/Race: African Americans have nearly twice the stroke incidence and mortality compared to European Americans (White et al., 2005)
• Family History of Stroke: Having two first-degree relatives with stroke results in HR = 1.25 CI 1.04-1.51 (Johansson et al., 2021)
• Education: Stroke risks are lower among those with university degrees HR = 0.85 CI 0.74-0.98 (Johansson et al., 2021)

Other Medical Conditions

• Atrial Fibrillation: This heart condition causes the heart’s upper chambers to beat irregularly, which can lead to formation of clots in the heart. These clots can then travel to the brain, causing strokes (Wolf, Abbot & Kannel, 1991).
• Sleep Apnoea: Additional strain on the heart and increase the risk of hypertension, subsequently stroke (Yaggi et al., 2005).

Question 2

Understand the pathophysiological mechanisms that lead to different types of stroke

Answer 2

Ischemic Stroke

Accounts for about 87% of all strokes, occurs when a blood clot blocks or narrows an artery leading to the brain, causing a reduction in blood flow (ischemia). Risk factors include hypertension, diabetes, smoking, dyslipidaemia, atrial fibrillation and lifestyle factors such as diet and exercise (Johansson et al., 2021).

• Thrombosis: When a blood clot (thrombus) forms directly in one of the arteries supplying blood to the brain. Associated with atherosclerosis, where fatty deposits (plaques) build up on the artery walls and either narrow the artery or cause a clot to form. More common in older adults
• Embolism: Blood clot forms away from the brain, commonly the heart, and is swept through the bloodstream to lodge in narrower brain arteries. Associated with heart problems like atrial fibrillation.
• Systemic Hypoperfusion: A generalised reduction in blood flow, related to severe drop in BP. can lead to watershed infarcts which affect the border zones between the major cerebral arteries

(Caplan, 2009) Mechanisms and types of ischemic stroke, emphasising thrombosis, embolism and systemic hypoperfusion

Haemorrhagic Stroke

When a blood vessel in the brain bursts leading to bleeding (Haemorrhage) either in or around the brain. Risk factors include hypertension, anticoagulant medication, heavy alcohol use and genetic factors

• Intracerebral Haemorrhage (ICH): Most common type, occurring when an artery in the brain bursts, flooding the surrounding tissue with blood. Leading to cell death in the affected area. Causes include hypertension, arteriovenous malformation or head injury.
• Subarachnoid Haemorrhage (SAH): Bleeding into the subarachnoid space, the area between the brain and the thin tissues covering it (dura). This type of stroke is commonly caused by bursting of an aneurysm (buldge in blood vessel caused by weakness in vessel wall), arteriovenous malformation and trauma
• Pressure Effects: The accumulation of blood puts pressure on the brain, causing direct damage to brain tissue which impairs function.
• Toxic Effects of Blood Breakdown Products: As the blood breaks down, it releases product that cause inflammation, cytotoxicity and further damage to the brain cells.
• Vasospasm: Particularly in SAH, where other blood vessels in the brain contract and narrow, causing additional ischemia

(Wong et al., 2016)

Question 3

Describe the vascular anatomy of the brain and its relation to the clinical features of stroke

Answer 3

Major Arterial Systems

1. Anterior Circulation

• Carotid System: This system includes the internal carotid arteries which bifurcate into the anterior cerebral arteries and middle cerebral arteries
• Anterior Cerebral Artery: Supplies the medial portions of the frontal loves and superior medial parietal lobes. Stroke in the ACA territory typically results in contralateral leg weakness and sensory loss due to its supply to primary motor and sensory areas of the leg.
• Middle Cerebral Artery: Supplies lateral aspects of the frontal, temporal and parietal lobes. An MCA stroke is the most common type of stroke and can cause contralateral paralysis and sensory loss, primarily affecting the face and arm. It can also result in aphasia (language expression and comprehension) if the dominant hemisphere is involved or hemineglect (reduced awareness of one side’s stimuli) if the non-dominant hemisphere is affected.

2. Posterior Circulation

• Vertebrobasilar System: Composed of the vertebral arteries, which join to form the basilar artery. The basilar artery then branches into the posterior cerebral arteries
• Vertebral and Basilar Arteries: Supply the brainstem and cerebellum. Strokes here can result in a variety of symptoms including dizziness, dysphagia (difficulty swallowing), dysarthria (weakness in speaking muscles), bilateral or alternating sensory and motor deficits (touch & taste) and cranial nerve palsies (nerve blood flow blockage).
• Posterior Cerebral Arteries: Supplies the occipital lobes and the bottom parts of the temporal lobes. Typically result in contralateral hemianopia (vision loss in one half of one eye) with macular sparing (only vision in the centre) due to the involvement of the visual cortex (occipital lobe)

Additional Vascular Components

• Circle of Willis: Circular anastomosis of arteries at the base of the brain that provides collateral circulation. It connects the anterior and posterior circulations. Provides source of blood flow during a stroke if one part of the network is blocked
• Penetrating Arteries: Small deep arteries branch from the surface arteries and are crucial in supplying deep structures like the basal ganglia, internal capsule, thalamus and parts of the white matter. Stroke in these arteries can result in small but strategically significant infarcts, often referred to as lacunar strokes
• Small Vessel Disease: Chronic hypertension, aging and other vascular risk factors can lead to lipohyalinosis, thickening and stiffening of the walls of these small arteries, reducing their ability to supply adequate blood to deep brain structures, contributing to vascular dementia and deep brain stroke.

Clinical Features of Stroke in Relation to Vascular Territories

• Cortical vs Subcortical Strokes: Cortex or deeper structures. Cortical strokes (ACA, MCA or PCA) often have more pronounced cognitive and sensory deficits, given the cortex’s role in processing higher-order functions. Subcortical strokes (involving penetrating arteries) tend to present with pure motor or pure sensory symptoms, or with specific syndromes like ataxic hemiparesis (weakness in face or body parts) or dysarthria (speech muscle weakness) - clumsy hand syndrome
• Anterior vs. Posterior Circulation Strokes: Anterior circulation strokes (carotid system) often result in speech and motor deficits, whereas posterior circulation strokes (vertebrobasilar system) can lead to complex visual and balance disturbances

(Caplan, 2009)

Question 4

Brain Lobe and Cortex Functions

Answer 4

Lobes

1. Frontal Lobe

• High-level cognitive functions such as reasoning, planning, decision-making and problem solving
• Controlling voluntary movement through primary motor cortex
• Broca’s area - speech production
• Emotions and impulse control

2. Parietal Lobe

• Primary somatosensory cortex for sensory processing such as touch, pressure, temperature and pain
• Spatial orientation and navigation
• planning actions and manipulating objects

3. Temporal Lobe

• Primary auditory cortex, processing auditory information
• Houses hippocampus in the medial temporal lobe = memory formation and retrieval
• Wernicke’s area = language comprehension
• Assist in recognising and processing the emotional content of language

4. Occipital Lobe

• Primary visual cortex, interpreting visual stimuli and information
• Recognition of colours, object movement and depth

Cortex

1. Cerebral Cortex

• The outermost layer of the brain
• Higher-order functions including thought, language and consciousness
• The cortex is characterised by gyri and sulci which increases its surface area

2. Motor Cortex

• Located in the posterior portion of the frontal lobe
• Controls voluntary movements by sending signals to muscles
• Organised somatotopically, meaning that specific parts of the motor cortex control specific parts of the body

3. Somatosensory Cortex

• Parietal lobe
• Processes sensory input from the body such as touch, pressure and temperature
• Also organised somatotopically

4. Prefrontal Cortex

• Anterior part of the frontal lobe
• Executive functions such as judgement, foresight, weighing the consequences of future actions, and overriding socially inappropriate responses