A stroke is a serious, potentially life-threatening condition that needs to be treated as a medical emergency. The first few hours after stroke onset are critical - the earlier a stroke is detected, the sooner treatment can be started, and the better the outcome and recovery.

Knowing and understanding the signs of a stroke is crucial, as is getting a quick diagnosis. A stroke MRI (magnetic resonance imaging) scan is one of the most important diagnostic tests doctors and specialists use to confirm a stroke diagnosis. In this article, we’ll discuss the signs of a stroke, the different types, and how a stroke MRI is so critical in diagnosing this dangerous health condition.

What is a Stroke?

A stroke occurs when blood flow to the brain stops or is interrupted. This blood flow is also called cerebral blood flow, cerebral meaning matters relating to the brain. A reduced cerebral blood volume means less oxygen and other essential nutrients reach the brain, which can then lead to serious damage to brain tissue. Such damage can lead to long-term symptoms such as problems with mobility and speech.

There are two main types of stroke:

Ischemic stroke - the most common type, accounting for around 85% of strokes, an ischemic stroke (also called a cerebral infarction) is caused by a blockage in a cerebral artery that’s responsible for blood flow to the brain, leading to a reduced level of oxygen reaching the brain cells. Such blockages are often due to a blood clot or deposits called plaques - they’re sometimes referred to as an arterial occlusion or an artery occlusion.
Hemorrhagic stroke - less common, a hemorrhagic stroke is caused by a rupture in a blood vessel that then bleeds into the skull and affects the blood supply to the brain.

The most common type of ischaemic stroke is an anterior circulation stroke, caused by a blockage in the anterior (to the rear of the brain) cerebral arteries (blood vessels) that affects the blood supply to a large area of the brain.

Another common type of ischaemic stroke is one that affects the middle cerebral artery (MCA), one of the largest arteries feeding the brain. An MCA stroke is characterised by a sudden interruption to the blood flow to the brain (ischaemia) or a complete stop to the blood flow (called an infarction). This can lead to an ischaemic penumbra (infarcted tissue that’s at risk of death or serious damage) and the death of the infarcted tissue.

Brain parenchyma strokes, also known as intracerebral haemorrhage, are characterised by cerebral ischaemia and bleeding in the brain’s parenchyma, or functional part.

A stroke that affects the white matter of the brain (the large network of nerve fibres that allow for the exchange of information necessary for the brain to do its work) can lead to problems with cognition (our ability to think, learn and reason) and emotional regulation.

The basal ganglia form the part of the brain that’s responsible for language, mood, movement and other critical functions. A stroke can affect the blood vessels that supply this area with blood. This can affect the way a person moves and expresses their emotions.

Symptoms

The symptoms of a stroke can start very suddenly, and include:

Facial weakness, usually on one side that may look like drooping or may affect your ability to smile or move your face
Weakness or numbness in one or both arms causing an inability to lift or hold your arms above your head
Slurred or confused speech

If you suspect a stroke, call 999 immediately.

When remembering the signs of a stroke, remember the acronym, FAST:

Face
Arms
Speech
Time to call 999

There are other signs that could indicate that you or someone nearby is having a stroke:

Complete paralysis down one side of the body
Numbness or weakness down one side of the body
Feeling dizzy, fainting or falling over for no reason
A sudden and severe headache
Blurred or lost vision
Feeling nauseous or being sick
Confusion
Memory loss
Difficulty speaking or remembering words

Stroke symptoms may be short-lived and stop very quickly. However, this could be the sign of a mini-stroke, also called a transient ischemic attack or TIA, and it’s still crucial that you seek medical attention as you could be at risk of a full stroke in the near future.

Can an MRI Scan Detect a Stroke?

A stroke MRI scan allows specialist radiologists and doctors to detect the signs of a stroke and what blood vessels and brain tissue may have been affected. An MRI scan can also inform doctors what type of stroke you’ve had, so that they can start the appropriate stroke treatment.

For the best chance of a successful outcome and treatment, a stroke MRI should be performed within the first few hours of stroke onset, ideally within the first four hours. However, an MRI scan can show signs of a stroke 24 hours later and beyond. Doctors categorise strokes based on how long ago they happened, ranging from immediate to chronic:

Immediate

A patient diagnosed with an immediate stroke may already be in hospital undergoing tests or treatment for a previous stroke or another medical condition. An MRI scan can confirm a stroke straight away, but may require further monitoring.

Early Hyperacute

An early hyperacute stroke is a stroke that’s been detected on a stroke MRI scan within six hours.

Late Hyperacute

A late hyperacute stroke is a stroke that’s been detected between six and 24 hours of it occurring.

Acute

An acute stroke is a stroke that’s been diagnosed via an MRI scan within 24 hours to one week.

Subacute

A subacute stroke occurred 1 to 3 weeks previous to having an MRI scan.

Chronic

Stroke patients diagnosed with a chronic stroke probably had a stroke three or more weeks prior to diagnosis.

What Does it Look Like on MRI?

An early stroke will show as changes in the brain’s water content, which can indicate swelling, bleeding, and blood clotting.

Brighter areas on a stroke MRI that coincide with the parenchymal part of the brain (called parenchymal enhancement) can indicate an ischaemic stroke, and highlights that there has been potential damage to the blood-brain barrier. This can lead to a swelling in the brain called a vasogenic oedema and will need to be treated straight away.

How Long Will a Stroke Show Up on an MRI?

The damage caused by a stroke can still show on an MRI years, even decades later.

Will an Old Stroke Show Up on an MRI?

Later, chronic strokes will still show on an MRI but instead of showing a change in fluid balance, they will show areas of damaged areas and shrinkage, characterised by white spots on a stroke MRI.

Does a Mini Stroke Show Up on an MRI?

An MRI scan will still show the signs of a mini-stroke, even if you’re unaware that you’ve had one.

How an MRI Scan Detects a Stroke

MRI scans use two different signals to produce detailed images inside the body—T1-weighted and T2-weighted signals. T1 signals show fluids as dark and the anatomy and structures of the brain in crisp images, while T2 signals show fluids brightly, highlighting swelling and lesions and detecting abnormalities. Experienced radiologists will use the signal changes between the two to diagnose a stroke and determine whether it’s been caused by a blockage (ischaemic) or a rupture (hemorrhagic).

An ischaemic acute infarction (a stroke that’s detected within 24 hours to a week, and the most common type) will also show as a high signal intensity on a diffusion-weighted imaging (DWI) MRI with a low signal intensity on an apparent diffusion coefficient (ADC) MRI. A perfusion-weighted stroke MRI helps doctors track contrast enhancement (that indicates damage) through the brain tissue. So-called perfusion imaging can also track the mean transit time (MTT) - the average time (in seconds) it takes for red blood cells to pass through a specific blood vessel.

Diffusion and perfusion MRI scans are used to confirm strokes, along with a low ADC value and other calculations. They may also use a diffusion perfusion mismatch calculation to predict how well you might respond to certain stroke treatments.

All of these terms may sound overwhelming, but your medical team will explain everything you need to know in a way that you’ll understand.

Diagnosing a Stroke

There are various stages to diagnosing a stroke, and they may all happen very quickly once you’ve arrived at hospital.

Recognising Symptoms

As we discussed above, a stroke can come on very quickly and is a medical emergency. Therefore, knowing the symptoms is extremely beneficial for getting medical attention quickly and starting the right course of treatment.

Emergency Assessment

As soon as an ambulance arrives (or you get to hospital), paramedics and doctors will begin to assess you. They will ask you or a loved one questions about your symptoms and when they started.

Physical Examination

Your medical team will also perform some physical tests including listening to your heart and taking your blood pressure.

CT Scan

An early CT, or computed tomography, brain scan uses x-rays and computer programming and can be used to diagnose a stroke. A type of CT scan called CT perfusion can help doctors assess blood flow to the brain and other parameters that are useful in confirming the type of stroke you’ve had.

MRI

A stroke MRI brain scan helps doctors establish if you’ve had an ischaemic or a hemorrhagic stroke. In the section above, we described how an MRI can diagnose a stroke, but essentially, doctors are looking for changes in MRI sequences.

During an MRI, you may have a dye injected into a blood vessel (during a process called magnetic resonance angiography using an iodinated contrast dye) that provides a clearer picture of the blood flow to and around the brain.

Your doctor will also use a process called fluid-attenuated inversion recovery (FLAIR) during an MRI scan. This process removes the image of the cerebrospinal fluid (the fluid that bathes the brain) to produce a more detailed picture of the brain’s water content. They may also use a measure called the apparent diffusion coefficient (ADC) to measure fluid movement, which can help detect swelling and brain tissue death.

Blood Tests

You will have some blood samples taken and these will look for signs of infection, how quickly your blood clots, and how high your blood sugar levels are.

Neurological Evaluation

A neurological evaluation will take place in the department of neurology, or brain health, by a doctor called a neurologist. They will assess all of your results which will help them determine your best course of treatment.

Electrocardiogram (ECG)

An ECG measures the electrical activity of the brain via small, sticky electrodes placed on your chest. It helps to detect any abnormalities in the heart rate that could be the cause of your stroke.

Echocardiogram

An echocardiogram uses sound waves to detect blood clots in the heart that could have potentially traveled via a blood vessel to the brain, causing your stroke.

Carotid Ultrasound

The carotid artery is the main artery in the neck supplying blood to the brain. An ultrasound of the carotid artery can reveal any blood clots or fatty plaques that may cause blockages that may have led to a stroke.

Cerebrospinal Fluid Analysis

Cerebrospinal fluid (CSF) is a fluid found in the brain and spinal cord where it protects and nourishes. Some stroke patients will have a CSF sample taken from their spine if their doctor thinks it necessary. This will then be tested for signs of infection or inflammation that could be linked to strokes.

Thrombophilia Testing

Thrombophilia is a condition that can lead to dangerous blood clotting. It doesn’t cause any symptoms until a blood clot forms, so most people with the condition don’t know they have it. If you have a family history of thrombophilia or your doctor thinks you may have the condition, you will have a blood test called a thrombophilia screen to see if that could be the cause of your stroke.

Causes of Strokes

There are a few health conditions that can increase your risk of having a stroke:

High blood pressure
High cholesterol
Diabetes
Obesity
Atrial fibrillation (a fast or irregular heartbeat)

You’re also at a higher risk if you’ve had a mini-stroke in the past.

You may also be considered at a higher risk of strokes if:

You’re over 50 years old
You’re from a black or South Asian background
You experience migraines
You have sickle cell disease
You live an unhealthy lifestyle with a poor diet and little exercise
You smoke
You consume large quantities of alcohol
You’re pregnant and have preeclampsia

Prognosis and Treatment

Your treatment and how well you recover from a stroke will depend on a number of factors, including:

Your general level of health and wellbeing
The type of stroke you had - ischemic or hemorrhagic
The time between having a stroke and diagnosis (whether it’s in an early acute phase, a subacute phase or a later, chronic phase)

Emergency treatment for an acute ischaemic stroke includes thrombolytic therapy (medicines administered through the blood vessels during a process called intravenous thrombolysis or intra arterial thrombolysis, that helps to reduce blood clots) or a procedure called a thrombectomy (surgery to drain fluid from the brain and remove blood clots). You will also be given long-term medications to help reduce your risk of blood clots and a further stroke, as well as medications to help lower your blood pressure and cholesterol if necessary.

Long-term blood pressure medications are also used to treat hemorrhagic stroke patients.

Having a stroke may leave you with speech, swallowing and mobility problems. Your medical team will help you with rehabilitation to help you back to as normal a life as possible. With the right help, some stroke patients fully recover, particularly if surrounding blood vessels can support normal blood flow to the brain - a process called collateral circulation.

Why an MRI Scan is a Good Option

A stroke MRI scan is capable of detecting very small abnormalities in the blood vessels of the brain and provides a very detailed image of the brain tissue and blood vessels. MRI scans are also useful for determining the type of stroke you may have had and for picking up a mini-stroke that could potentially be missed on a computed tomography CT scan. Since an MRI scan doesn’t use x-rays or radiation, they don’t carry the risk of radiation exposure and can be used more than once to monitor treatment.

Find an MRI Scan for a Stroke

A stroke, including a mini-stroke, is a medical emergency - if you suspect you or someone nearby is having a stroke, seek medical attention immediately. If you’re looking to have a private stroke MRI scan or a second opinion, book a private MRI with us today. Sometimes it can feel overwhelming when it comes to making decisions about your health or that of a loved one. If you're unsure if an MRI scan is the right scan, book an appointment with one of our private consultants to help you decide.

References

Website, N. (2024b, September 19). Stroke. nhs.uk. https://www.nhs.uk/conditions/stroke/

NHS inform. (2024, October 14). Stroke | NHS inform. NHS Inform. https://www.nhsinform.scot/illnesses-and-conditions/brain-nerves-and-spinal-cord/stroke/

Rd, C. W. (2023, September 25). How long will a stroke show up on an MRI? https://www.medicalnewstoday.com/articles/how-long-will-a-stroke-show-up-on-an-mri

Stroke - Diagnosis and treatment - Mayo Clinic. (n.d.). https://www.mayoclinic.org/diseases-conditions/stroke/diagnosis-treatment/drc-20350119

Murphy, A., & Gaillard, F. (2011). Ischaemic stroke. Radiopaedia.org. https://doi.org/10.53347/rid-13437

Can an MRI Scan Diagnose a Stroke?