How does a stroke occur?

A stroke is the sudden death of brain cells. It is a medical emergency that occurs due to lack of oxygen to the brain, which is caused by an interrupted or reduced blood flow to your brain.

What are the 3 types of strokes?

1. Ischemic stroke

- An ischemic stroke occurs when blood supply to the brain is disrupted by blocked/ narrowed blood vessels caused by the build-up of fatty deposits in these vessels. This type of stroke can also occur when blood clots in the brain's blood vessels block blood flow to the brain.

Some factors that may lead to ischemic strokes include:

• Uncontrolled high blood pressure
• Atherosclerosis
• High cholesterol
• Irregular heartbeat
• Sickle cell anemia
• Diabetes
• Smoking

Ischaemic strokes are more common than hemorrhagic strokes. (around 87% of strokes are ischaemic)

Symptoms

• Issues with vision (e.g. partial blindness/ double vision)
• Issues with movement (weakness/ paralysis in limbs)
• Dizziness/ vertigo (the feeling that everything around you is spinning)
• Loss of coordination
• One side of the face drooping while the other side is normal

There are two types of ischaemic strokes: thrombotic and embolic.

A. Thrombotic stroke

A thrombotic stroke occurs when a thrombus (blood clot) forms in the arteries supplying blood to the brain. This blocks the flow of oxygenated blood to the brain, causing brain cells to die. This may also result in a stroke.

Depending on the size of the obstructed blood vessel, thrombotic stroke can be divided into two categories: large-vessel thrombosis and small vessel thrombosis

• Large-vessel thrombosis: Thrombus is found in one of the larger arteries that supply blood to the brain (e.g. carotid artery, middle cerebral artery)
  • Typically causes serious symptoms and long-term impacts such as: aphasia (being unable to understand speech or talk) and hemiparesis (weakness on one side of the body)
• Small-vessel thrombosis: Thrombus is found in one of the smaller and deep-penetrating arteries
  • Only affects a limited area of the brain, and therefore effects are more minor
  • However, it may have a serious impact on daily life if the region of the brain impacted is responsible for important cognitive functions

B. Embolic stroke

An embolic stroke occurs when a blood clot formed elsewhere in the body (usually the heart/ arteries at the upper chest and neck) breaks loose and travels to the brain via the bloodstream. When it reaches a blood vessel too narrow for it to pass through, the blood clot gets lodged in the artery, blocking the flow of blood.

These blockages, known as emboli, may be caused by air bubbles, fat globules, plaque or an abnormal heartbeat. When the heart does not function effectively, blood may pool and clot at certain areas, forming emboli.

2. Transient Ischemic Attack (TIA)

A transient ischemic attack (TIA), also known as a ministroke, is similar to an ischemic stroke: it occurs when a blood clot blocks or reduces blood flow to your brain, or when you have a partially blocked/ narrowed artery leading to your brain. This causes a temporary decrease in blood flow to your brain, leading to temporary symptoms similar to that of a stroke. Having a TIA means that you have an increased risk of having a stroke in the future.

3. Hemorrhagic stroke

A hemorrhagic stroke occurs when a blood vessel in your brain leaks or ruptures. Some factors that may lead to hemorrhagic strokes include:

• Uncontrolled high blood pressure
• Overtreatment of blood thinners (that prevent blood clots - anticoagulant)
• Bulges in blood vessels that eventually lead to ruptures (aneurysm)
• Trauma (e.g. due to car accidents)
• Protein deposits in blood vessels
• Ischemic stroke that leads to hemorrhage - the escape of blood from a ruptured blood vessel

Symptoms

• Total/ limited loss of consciousness
• Nausea, vomiting
• Sudden, severe headache
• Seizures
• Issues with movement (weakness/ paralysis in limbs)
• Loss of vision
• Loss of balance and coordination
• Difficulty speaking and/or swallowing
• Dizziness/ vertigo (the feeling that everything around you is spinning)
• Confusion, disorientation

There are two types of hemorrhagic strokes: intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH).

A. Intracerebral hemorrhage (ICH)

An ICH occurs when there is bleeding within the brain tissue, due to a rupture of blood vessels (aneurysm) in the brain. As blood bleeds into the brain, the part of the brain where the ruptured blood vessel was supposed to deliver oxygen now suffers from a lack of oxygen and its cells begin to die.

At the same time, more blood begins to collect in the brain tissue, forming a blood clot (also known as hematoma). This blood clot increases pressure on the brain, which can crush the brain against the skull, or cause the brain to shift.

ICH is the cause of 10% of strokes, with a 40% risk of death. It is twice as common as a subarachnoid hemorrhage (SAH).

B. Subarachnoid hemorrhage (SAH)

A SAH occurs when there is bleeding in the space that surrounds the brain (also known as the subarachnoid space), most often due to a rupture of blood vessels (aneurysm) on the surface of the brain.

As blood builds up around the brain and inside the skull, pressure on the brain is increased, and vital brain tissue could be compressed/ displaced.

How can I confirm that I have a stroke?

After you've been sent to the hospital, the doctors may conduct some scans and tests to identify which type of stroke you are suffering from, as well as to confirm that you are not suffering from other possible illnesses that may have similar symptoms as stroke.

Clinical tests

• Physical examination
  • The doctor may listen to your heartbeat and check your blood pressure
  • A neurological exam may also be run to examine the effects of a potential stroke on your nervous system
• Blood tests
  • These tests may check the rate at which your blood clots, your blood sugar level, and whether you have an infection

Scans

• Computerized tomography (CT) scan
  • A CT scan uses X-rays to create a detailed image of your brain, allowing doctors to identify any visible blood clots/ bleeding in the brain
• Magnetic resonance imaging (MRI) scan
  • An MRI makes use of a magnetic field and radio waves to construct a detailed image of your brain, allowing doctors to check for any brain tissue damage
  • This scan also helps to rule out other underlying reasons that may have caused the stroke, ascertaining that a blood clot lodged in an artery is the main reason why the stroke had occurred
• Cerebral angiography
  • A thin catheter is inserted into your arteries (commonly through your groin) and guided into the major arteries (e.g. carotid or vertebral artery). A contrast dye is also injected into the arteries to make the blood vessels easily visible in X-ray images
  • This gives a detailed view of the arteries in your brain and neck
  • This helps to rule out aneurysms as the cause of bleeding in the brain
• Echocardiogram
  • Sound waves are used to create detailed images of the heart
  • Blood clots that were formed in the heart and had broken loose and become lodged in the arteries leading to the brain may also be identified
• Lumbar puncture
  • A hollow needle is inserted into the space around the spinal column in the lower back, and cerebrospinal fluid (CSF) is withdrawn
  • This can help diagnose hemorrhagic stroke

For new patients with stroke, diagnosis for stroke also takes into account one's risk factors. Some risk factors include:

• Older age
  • After the age of 55, the risk of having a stroke more than doubles for each subsequent decade of life
• Race
  • E.g. African-Americans have a higher risk of stroke than whites, partly because the African-American population has a higher number of people with high blood pressure (which is another risk factor for stroke)
• Gender
  • Men suffer from strokes more often than women, but more women die from stroke than men
• Family history
  • If you have family members who have suffered from stroke, your risk of having a stroke will be higher
• High blood pressure
  • High blood pressure can damage blood vessels that supply blood to the brain, leading to potential ruptures in the brain's blood vessels
• Heart disease, abnormal heart rhythm
• Diabetes
• High red blood cell count
  • A high red blood cell count thickens the blood, increasing the likelihood for blood clots and subsequently, strokes
• High cholesterol
  • High cholesterol can lead to a build-up of plaque inside blood vessels, contributing to the thickening/ hardening of blood vessels (atherosclerosis) that decreases blood supply to the brain
• Lack of exercise, obesity
• Smoking
• Excessive alcohol use

For more information or if you require a medical consultation, please contact My Healthcare Collective here.