What is brain stroke and how does it occur?

Recently the American Heart Association/ Stroke Association has updated the meaning of the “stroke”. It refers to the death of cells due to a block of blood supply in the brain, spinal cord, or retina. As we can acknowledge, this definition does not need the presence of symptoms or signs. It is because there can be silent stroke and now we can identify with new advanced imaging technology.

Stroke is a brain disease,

not a heart disease.

Stroke is the second leading cause of death and the third leading cause of disability in the world. As much as 70 percent of stroke events are thought to occur in low-middle income countries. On average, a stroke occurs 15 years earlier among people living in those countries. During the past four decades, stroke incidence among low-middle income countries has doubled while it has halved in high-income countries1.

A stroke occurs as a result of brain cell death due to an interruption of blood supply to a part/s of the brain. We will discuss this in module 2. 

Stroke warning signs are easy to detect. The common ones are drooping one eyelid, inability or difficulty of raising one or both arms, and slurred speech; there are more. We will discuss these in module 3.

However, a stroke can also occur without any observable changes.

Stroke results in a range of disabilities of the affected person and at least half of these disabilities persist permanently for life, if not treated early. It exerts an enormous burden not only on the person affected but the whole family, and the society. We will discuss various kinds of disabilities in detail and what we can do to rehabilitate those in Part II of this course. 

1.2. What happens in a stroke?

A stroke cuts off blood supply to a part of the brain. (You can learn more about the brain by joining the “journeys to the brain” series). Within minutes, the neuron cells in the affected area begin to die at a rate of 32,000 per each passing second. In terms of minutes, the number amounts to about two million neuron cells per minute2.

Stroke kills about 32,000 neurons in each passing second.

Jeffrey L. Saver (2006): “Time is Brain”: Quantified; Stroke Journal. 2006;37(1): 263-266.(message creator:https://www.strokecarer.com/)

The only way to save the rest of the cells threatened with death is to restore the interrupted blood supply as soon as possible. This can only be done in a hospital with adequate facilities.

1.3. Types of stroke

A stroke usually occurs either due to a block in a supply route or a burst of the supply route’s wall.

Stroke can occur due to a block inside an artery to the brain or a burst of its wall.

1.3.1. Ischemic stroke

Ischemic stroke occurs due to a block by a blood clot inside the supply route. The extent of the damage depends on where the clot clogs the blood supply system inside the brain. If a clot is a bigger one, it clogs a larger artery and blocks the blood supply to a larger area of the brain. If the clot is a smaller one, it may travel as far higher up as possible until it clogs a smaller branch of a smaller artery.

Figure 1: How ischemic stroke occurs (source: National Heart, Lung, and Blood Institute from Wikimedia commons: this work is on the public domain)
How a blood clot forms

A roughened wall of an artery triggers blood clot formation. The roughening begins with fat deposition at one place of the wall. Then, it hardens with calcium and cholesterol deposits. The process continues slowly but surely forming a plaque there. This thickening narrows the lumen and roughens the surface. Plaque build-up can occur anywhere; however, strokes are commonly associated with plaque build-up in the neck vessels – carotid arteries as shown in Figure 1. 

The following video clip from the British Heart Foundation explains simply how arterial thickening occurs and the factors that facilitate the process.

How arterial thickening triggers blood clot formation (source: British Heart Foundation)

A clot can even originate inside the heart particularly among those with heart problems and travel into the brain.

In the US, about 80 percent of all strokes are in this nature according to the National Institute of Neurological Disorders and Stroke3. In low-middle income countries, this percentage is about 66 percent1.

1.3.2. Hemorrhagic stroke

When a stroke occurs due to a burst of the vessel wall, we call it a “hemorrhagic stroke” (Figure 2). As a result, blood seeps out of the vessel, and oxygen and food supply to neurons interrupt. The bleeding exerts pressure on the area causing more damage.

Figure 2: How hemorrhagic stroke occurs (source: Heart Lung and Blood Institute); this work is on the public domain)

However, there is another 5-10 percent of people who develop a stroke due to an unknown reason4.

1.4. What is a “mini-stroke” TIA (Transient Ischemic Attack)?

In this situation, the stroke signs and symptoms last less than 24 hours; most often, less than an hour. Hence, it is also called “Transient Ischemic Attack” (TIA). What happens here is that the clot that blocks the supply route disappears after a brief time.

However, it is a dire warning; it will certainly return as a full-blown stroke, often within the first week after the TIA, if not treated5.

Therefore, a mini-stroke should also be considered as a medical emergency.

In the following video clip, Professor Peter Rothwell explains why we should a mini-stroke also as a medical emergency.

An educational video clip on mini-stroke (source: Stroke Association)

However, if the effects last more than 24 hours, it is considered a stroke. Ideally, anyone who experience a mini-stroke should not drive or operate a machinery for a month. In some countries it is the law.

Do not drive after a mini-stroke at least for a month. In some countries, it is the law.

1.5. Who are at high-risk?

Some are at higher risk for stroke. We can reduce the risk by modifying some risk factors while others are non-modifiable. The source of the following list is the National Institute of Neurological Disorders and Stroke3.

Stroke can strike even the very young; no one is immune.

Non-modifiable risk factors
  • Age: The risk doubles every passing decade from 55 to 85. However, it can also occur in childhood6.
  • Sex: Men are at higher risk in young and middle age. In older ages, however, the risk is equal.
  • Ethnicity: some ethnic groups are at higher risk; for example, African-Americans and Hispanics experience stroke events more than Caucasians.
  • Family history
Modifiable risk factors

There are some risk factors that we can reduce the risk. Those are as follows;

  • High Blood Pressure: This is one of the most potent risk factors we can easily modify.
  • Diabetes
  • High cholesterol
  • Cigarette smoking: This raises the ischemic stroke risk by two-fold and hemorrhagic stroke risk by four-fold.
  • Physical inactivity and obesity
  1. Johnson, W., Onuma, O., Owolabi, M. & Sachdev, S. Stroke (2016): a global response is needed. Bulletin of the World Health Organization 94, 634–634A, https://doi.org/10.2471/BLT.16.181636.
  2. Jeffrey L. Saver (2006): “Time is Brain”: Quantified; Stroke Journal. 2006;37(1): 263-266.
  3. National Institute of Neurological Disorders and Stroke (NINDS): Basic facts: preventing stroke; NIH; 2020. Accessed on September 16, 2020.
  4. Donkor E.S. (2018): Stroke in the 21st Century; Stroke Res Treat.: published online.
  5. British Medical Best Practice; accessed on September 20, 2020.
  6. Vrudhula A, Zhao J, Liu RToo Young to Have a Stroke?—a Global Health CrisisStroke and Vascular Neurology 2019;4:doi: 10.1136/svn-2019-00029.


Author: Prasantha De Silva

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