What Is a Stroke?

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A stroke is a medical emergency that occurs when a blood clot or damaged blood vessel disrupts blood flow to the brain, ultimately affecting its function. The brain needs constant blood flow to receive oxygen and nutrients, and a stroke (sometimes called a “brain attack”) can cause severe complications in just a few minutes.

Brain cells begin to die shortly after blood flow is interrupted, resulting in loss of brain function. The resulting symptoms—including impaired movement, speech, memory, emotional control, and essential bodily functions like bowel control—depend on the size and location of the stroke. Small strokes may cause localized problems like weakness in an arm or leg, while larger strokes can cause paralysis, loss of speech, and even death.

Types of Stroke

The two main types of strokes, called ischemic strokes and hemorrhagic strokes, are defined by what disrupts blood flow to the brain. A third common type of stroke is called a transient ischemic attack (TIA) or "mini stroke."

Ischemic strokes

In an ischemic stroke, a blood clot or plaque deposit blocks one of the vital blood vessels in the brain, interrupting blood flow. Depending on the origin of the blockage, ischemic strokes may be classified as:

  • Thrombotic: A clot forms in the arteries supplying blood to the brain.
  • Embolic: A clot forms somewhere in the body and travels to the brain.

Thrombotic strokes may occur after one or more TIAs, while embolic strokes often occur without warning.

Hemorrhagic strokes

In a hemorrhagic stroke, a blood vessel in the brain bursts, spilling blood into the surrounding tissues. The pressure from the leaked blood damages the brain cells. Hemorrhagic strokes are divided into types depending on the location of the bleeding:

  • Intraparenchymal: Bleeding originates from blood vessels in the brain.
  • Subarachnoid: Bleeding originates from the space between the brain and surrounding membranes.

Intracerebral hemorrhages are usually the result of high pressure and progress rapidly with serious complications. Subarachnoid hemorrhages typically result from an aneurysm (swelling in the wall of an artery), from a congenital disorder called arteriovenous malformation, or from traumatic injuries.

Learn more about hemorrhagic strokes.

Transient ischemic attack (TIA)

Known as a mini-stroke, a TIA is like an ischemic stroke, but the blockage is temporary—often less than five minutes. Mini strokes may not lead to lasting complications but must be treated to ensure that the blockage doesn't provoke a full stroke later.

Other types of stroke
  • Brainstem stroke: A brainstem stroke is defined by its location rather than what caused it. Brainstem strokes can be either ischemic or hemorrhagic and are the most deadly type of stroke because they affect the brainstem, which controls survival functions like breathing and heartbeat.
  • Cryptogenic stroke: Cryptogenic is a medical term meaning "unknown cause." If you have a cryptogenic stroke, it means that even after testing, doctors couldn't identify the cause of the stroke and exhausted known dangerous diagnoses.

Stroke Symptoms

Strokes cause lasting damage in a short amount of time, so getting immediate help is crucial. Knowing the early signs of a stroke can help you get treatment before it's too late. If you see the following stroke symptoms in yourself or someone else, seek medical attention immediately:

  • Weakness or numbness of the face, arms, or legs, especially on one side of the body.
  • Confusion or difficulty speaking or understanding.
  • Problems with vision, such as dimness or loss of vision in one or both eyes.
  • Dizziness or problems with balance or coordination, including walking difficulty.
  • Loss of consciousness or seizure.
  • Severe headaches with no other known cause, especially if sudden onset.

Strokes don't always present all these symptoms, so even if you only see a few signs of stroke or if your stroke symptoms go away, it's best to seek help. Less common stroke symptoms include:

  • Sudden nausea or vomiting not caused by a viral illness.
  • Brief loss or change of consciousness, such as fainting, confusion, seizures, or coma.

Ischemic vs Hemorrhagic Stroke Symptoms

The signs and symptoms of stroke are mostly the same for the two major types of stroke. However, there can also be slight differences. Those experiencing an ischemic stroke may have numbness or weakness on one side of the face or body and have difficulty with balance, vision, and speaking. A sudden and severe headache is often a key sign of hemorrhagic stroke but doesn't always occur in other types of strokes.

What are the early signs of a stroke? DaMarcus Baymon, MD, Emergency Medicine Physician at Brigham and Women's Hospital and Faulkner Hospital, describes how to quickly identify stroke symptoms using the F.A.S.T. acronym.

How to Stop a Stroke in Progress

A stroke is a life-threatening emergency. If you suspect that you or someone else is having a stroke, call 911. Some treatments can help with a stroke in progress, but they aren't home remedies. Get help immediately because treatment is most effective within three hours of the first symptoms.


The FAST technique can help you evaluate early signs of stroke and get help in time. Strokes are life-threatening emergencies that require immediate medical attention. Call 911, make a note of when the symptoms started, and "act FAST" to assess the situation:

  • Face: Does the face droop when you ask the patient to smile?
  • Arms: Is the patient able to raise both arms equally well?
  • Speech: Is the patient's speech slurred or strange when asked to repeat a basic phrase?
  • Time: Getting medical attention quickly is imperative, so call 911 immediately.

What Causes a Stroke?

A stroke occurs when a blood clot limits the flow of blood and oxygen to the brain or when a blood vessel bursts or leaks. A blood clot can have many causes, including poor diet, smoking, or excessive alcohol use. A blood vessel can burst due to conditions like diabetes or high blood pressure, damaging or weakening the arteries and making them more susceptible to rupturing.

Stroke Risk Factors

Both lifestyle factors and other medical conditions can put you at higher risk for stroke. Risk factors that can be controlled through lifestyle changes or medical treatment include:

  • Diabetes: Diabetes can damage blood vessels over time because of high blood sugar.
  • Alcohol: The more alcohol you consume, the greater your risk.
  • Heart disease: Heart disease can increase your risk of plaque buildup and clots.
  • Heart rhythm: Heart rhythm disorders can cause blood clots that can lead to stroke.
  • Hypertension: High blood pressure can damage or weaken blood vessels.
  • Red blood cell count: A high red blood cell count thickens the blood and can cause clots.
  • Cholesterol: High cholesterol causes plaque buildup and hardening of the arteries.
  • Body composition: Obesity contributes to an increased risk of stroke.
  • Activity: A sedentary lifestyle and lack of exercise can increase risk.
  • Smoking: Smoking doubles your risk for stroke.

Other risk factors for stroke that can't be controlled include:

  • Age: As people get older, their risk of stroke increases.
  • Gender: Men are more likely to have a stroke.
  • Previous stroke: Once you have a stroke, you are at a much higher risk of having another one.
  • Genetics: A family history of strokes increases your risk.

Effects of a Stroke

The effects of a stroke vary widely depending on the part of the brain affected. The most common side effects of a stroke are impairments in speech, reduced motor skills, paralysis on one side of the body, and difficulty communicating. A stroke can also cause behavioral changes, vision problems, and memory loss.

Stroke Prevention

A stroke is a serious medical issue, so it’s much better to prevent a stroke than treat one. Different approaches can reduce your risk of stroke.


Two kinds of medicines—antiplatelet drugs and anticoagulants—can reduce your risk of stroke. Please ask your medical providers what is appropriate for your health and stroke prevention.


May lifestyle factors can reduce your risk of stroke. Some of the most effective are:

  • Quit smoking
  • Eat a healthy diet
  • Get regular exercise
  • Limit your alcohol and drug use
  • Get treatment for sleep apnea
  • Maintain a healthy blood pressure

Surgical options can help treat or prevent a stroke. For example, a surgeon may perform preventative stroke surgery by inserting a tube called a stent in the neck artery to help maintain blood flow by keeping narrow blood vessels open. The stent may have a balloon that can inflate to push plaque against the sides of the artery and reduce blockage.

Emergency surgery for stroke can save your life. Your care team will determine the best surgery for your stroke (also known as cerebrovascular accident, CVA) based on the location and extent of the brain area affected. They may perform an operation to:

  • Drain blood and reduce pressure on the brain.
  • Break up blood clots and restore normal blood flow.
  • Correct malformations in the vascular system called AVMs that impede normal blood flow to the brain.

Learn more about surgery for stroke and other stroke treatments.

FAQs about Strokes

Can you have a stroke and not know it?

Yes. "Silent strokes" don't present obvious symptoms of stroke but still cause brain damage. Loved ones and acquaintances may notice changes in memory or cognitive abilities as the stroke affects the brain. If you notice these changes in someone, seek medical attention immediately.

What is a mini stroke?

A mini stroke is another name for a transient ischemic attack (TIA). This type of stroke lasts only a few minutes but is still serious and may be a precursor to a full ischemic stroke.

Are strokes hereditary?

Family history is a risk factor for stroke, but strokes aren't hereditary in the way hair color is. Good lifestyle choices can help counteract the increased likelihood of stroke that comes with family history.

Can you have a stroke with low blood pressure?

Yes. Hemorrhagic strokes are more common in those with high blood pressure, but you can still have a stroke with normal or low blood pressure. Some research suggests that low blood pressure may increase the risk of ischemic strokes and may increase complications of a stroke.

What is the difference between a heart attack and a stroke?

Heart attack and stroke are similar in that they both involve reduced or blocked blood flow to vital organs. A heart attack occurs when blood flow to the heart is interrupted. A stroke occurs when blood flow to the brain is interrupted, which is why strokes are sometimes referred to as "brain attacks."

Are the symptoms of stroke in women the same as in men?

The risk of stroke increases with age. Because women generally live longer than men, more women experience strokes. While the main symptoms of a stroke in women are the same as in men, women more commonly report these symptoms of a stroke:

  • Difficulty breathing
  • Feeling weak or fainting
  • Hiccups
  • Seizures
  • Hallucinations
  • Sudden behavioral changes
  • Vomiting or nausea
Is heat stroke the same as a stroke?

Despite the similar name, heat stroke is a very different condition. Heat stroke means that the core body temperature has risen over 104°F. It doesn't involve blocked blood flow to the brain.

Can a stroke cause dementia?

Strokes can cause a form of dementia if they provoke enough damage to the brain. They are commonly associated with a kind of cognitive decline called vascular dementia. Not everyone who has a stroke will develop dementia, but strokes increase your likelihood.

Request an Appointment

You can schedule an appointment with our neurology team by calling 617-207-6143 or by submitting a request through our secure online form. We're here to support you every step of the way.

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