A stroke, also known as a cerebrovascular accident or CVA is when part of the brain loses its blood supply and the part of the body that the blood-deprived brain cells control stops working. This loss of blood supply can be ischemic because of lack of blood flow, or hemorrhagic because of bleeding into brain tissue. A stroke is a medical emergency because strokes can lead to death or permanent disability.
There are opportunities to treat ischemic strokes but that treatment needs to be started in the first few hours after the signs of a stroke begin. The patient, family, or bystanders, should call 9-1-1 and activate emergency medical services immediately should a stroke be suspected.
What causes a stroke?
The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. As a result of the deprived blood and oxygen, the cells of that part of the brain die and the part of the body that it controls stops working. Typically, a cholesterol plaque in one of the brain’s small blood vessels ruptures and starts the clotting process.
Risk factors for narrowed blood vessels in the brain are the same as those that cause narrowing blood vessels in the heart and heart attack (myocardial infarction). These risk factors include:
- high blood pressure (hypertension),
- high cholesterol,
- diabetes, and
Another type of stroke may occur when a blood clot or a piece of atherosclerotic plaque (cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose, travels through the bloodstream, and lodges in an artery in the brain. When blood flow stops, brain cells do not receive the oxygen and glucose they require to function and a stroke occurs. This type of stroke is referred to as an embolic stroke.
For example, a blood clot might originally form in the heart chamber as a result of an irregular heart rhythm, like atrial fibrillation. Usually, these clots remain attached to the inner lining of the heart, but occasionally they can break off, travel through the bloodstream (embolize), block a brain artery, and cause a stroke. An embolism, either plaque or clot, may also originate in a large artery (for example, the carotid artery, a major artery in the neck that supplies blood to the brain) and then travel downstream to clog a small artery within the brain.
A cerebral hemorrhage occurs when a blood vessel in the brain ruptures and bleeds into the surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) causes stroke symptoms by depriving blood and oxygen to parts of the brain in a variety of ways. Blood flow is lost to some cells.
Additionally, blood is very irritating and can cause swelling of brain tissue (cerebral edema). Edema and the accumulation of blood from a cerebral hemorrhage increases pressure within the skull and causes further damage by squeezing the brain against the bony skull. This further decreases blood flow to brain tissue and its cells.
In a subarachnoid hemorrhage, blood accumulates in the space beneath the arachnoid membrane that lines the brain. The blood originates from an abnormal blood vessel that leaks or ruptures. Often this is from an aneurysm (an abnormal ballooning out of the blood vessel). Subarachnoid hemorrhages usually cause a sudden severe headache, nausea, vomiting, light intolerance, and stiff neck. If not recognized and treated, major neurological consequences, such as coma, and brain death may occur.
Another rare cause of stroke is vasculitis, a condition in which the blood vessels become inflamed causing decreased blood flow to parts of the brain.
There appears to be a very slight increased occurrence of stroke in people with migraine headache. The mechanism for migraine or vascular headaches includes narrowing of the brain blood vessels. Some migraine headache episodes can even mimic stroke with loss of function of one side of the body or vision or speech problems. Usually, the symptoms resolve as the headache resolves.
What are the types of stroke?
Strokes are usually classified by what mechanism caused the loss of the blood supply, either ischemic or hemorrhagic. A stroke may also be described by what part of the brain was affected (for example, a right temporal stroke) and what part of the body stopped working (stroke affecting the left arm).
An ischemic stroke is caused by an artery in the brain being obstructed or blocked, preventing oxygen-rich blood from being delivered to brain cells. The artery can be blocked in a couple of ways. In a thrombotic stroke, an artery can narrow over time because of cholesterol buildup, called plaque. If that plaque ruptures, a clot is formed at the site and prevents blood from passing to brain cells downstream, which are then deprived of oxygen.
In an embolic stroke, the artery is blocked because of debris or a clot that travels from the heart or another blood vessel. An embolus or embolism is a clot, a piece of fatty material or other object that travels within the bloodstream that lodges in a blood vessel to cause an obstruction.
Blood clots that embolize usually arise from the heart. The most common cause of these blood clots is a heart arrhythmia called atrial fibrillation, where the upper chambers of the heart, the atria, do not beat in an organized rhythm. Instead, the chaotic electrical rhythm causes the atria to jiggle like a bowl of Jell-O. While blood still flows to the ventricles (the heart’s lower chambers) to be pumped to the body, some blood along the inner walls of the atrium can form small blood clots. If a clot breaks off, it can travel or embolize to the brain, where it can block blood flow to a part of the brain and cause a stroke.
The carotid arteries are two large blood vessels that provide the brain with blood supply. These arteries can narrow, or develop stenosis, with cholesterol plaque that may build up over time. The surface of the plaque is irregular and bits of debris can break off and embolize to the brain to block blood vessels downstream and deprive brain cells of oxygen-rich blood.
When a blood vessel leaks and spills blood into brain tissue, those brain cells stop working. The bleeding or hemorrhage is often due to poorly controlled high blood pressure that weakens the wall of an artery over time. Blood may also leak from an aneurysm, a congenital weakness or ballooning of an artery wall, or from an AVM (arteriovenous malformation), a congenital abnormality where an artery and vein connect incorrectly. The bleeding can form a hematoma that directly damages brain cells and may also cause swelling that puts further pressure on surrounding brain tissue.
Describing a stroke by anatomy and symptoms
There are four major arteries that supply the brain with blood.
- The right and left carotid artery are located in the front of the neck and their pulse can be felt with the fingers.
- The right and left vertebral arteries are encased in bone as they run through the vertebrae in the neck. As the two enter the brain, they join to form the basilar artery.
- The carotid arteries and the vertebrobasilar arteries join to form the Circle of Willis at the base of the brain and from this circle, arteries branch off to supply the brain with blood.
The left side of the brain controls the right side of the body and vice versa. Speech tends to be located in the dominant hemisphere, most often the left brain.
The anterior and middle cerebral arteries provide blood supply to the front two-thirds of the brain, including the frontal, parietal, and temporal lobes. These parts of the brain control voluntary body movement, sensation, speech and thought, personality, and behavior.
The vertebral and basilar arteries are considered the posterior circulation and supply the occipital lobe where vision is located, the cerebellum that controls coordination and balance, and the brainstem that is responsible for the unconscious brain functions that include blood pressure, breathing, and wakefulness.
What are the risk factors for stroke?
Overall, the most common risk factors for stroke are:
- high blood pressure,
- high cholesterol,
- diabetes, and
- increasing age.
Heart conditions like atrial fibrillation, patent foramen ovale (hole in the heart), and heart valve disease can also be the potential cause of stroke.
When stroke occurs in younger individuals (less than 50 years old), less common risk factors to be considered include illicit drugs, such as cocaine or amphetamines, ruptured aneurysms, and inherited (genetic) predispositions to abnormal blood clotting.
An example of a genetic predisposition to stroke occurs in a rare condition called homocystinuria, in which there are excessive levels of the chemical homocystine in the body. Scientists are trying to determine whether the non-hereditary occurrence of high levels of homocystine at any age can predispose to stroke.
What are the warning signs and symptoms of a stroke?
There may be no warning signs of a stroke until it occurs. It is why high blood pressure (hypertension), one of the risk factors for stroke, is called the silent killer.
Some patients may experience transient ischemic attack (TIA) that can be thought of as a stroke that has resolved itself. The symptoms may be mild or dramatic and can mimic a stroke with weakness, numbness, facial droop, and speech difficulties, but these symptoms may only last a few minutes.
TIAs should not be ignored since they may offer an opportunity to look for potentially reversible or controllable causes of stroke. As well, there is no guarantee that the symptoms of stroke will resolve on their own. For that reason, a TIA should be considered an emergency and medical care should be accessed immediately.
Amaurosis fugax describes the temporary loss of vision in one eye that occurs because of an embolus of blood clot or debris to the artery that supplies the eye. While it only involves vision, this situation should be considered a type of TIA.
What are the signs and symptoms of a stroke?
Symptoms of stroke depend upon what area of the brain has stopped working due to loss of its blood supply. Often, the patient may present with multiple symptoms including the following:
- Acute change in level of consciousness or confusion
- Acute onset of weakness or paralysis of half or part of the body
- Numbness of one half or part of the body
- Partial vision loss
- Double vision
- Difficulty speaking or understanding speech
- Difficulty with balance and vertigo
The symptoms of ischemic and hemorrhagic stroke may be the same, but patients with hemorrhagic stroke may also complain more of headache and vomiting.
What is the treatment for stroke?
A stroke is a medical emergency, but prompt intervention can restore blood supply to the brain if stroke patients receive medical care early enough. The good news is that we have a solution for you.