How Healthcare Providers Find the Cause of a Cryptogenic Stroke

A cryptogenic stroke is a stroke of unknown cause. This means that the stroke cannot be attributed to any specific cause or risk factor, even after thorough testing. Before labeling any stroke a cryptogenic stroke, your stroke team will search for the common and uncommon causes of stroke. The most common causes of stroke include smoking, heart disease, high blood pressure, vascular disease, and high cholesterol.

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What Is a Stroke?

A stroke is brain damage due to the interruption of blood flow to a region of the brain. It is among the top causes of death and disability in the United States. A stroke occurs when a blood vessel that carries oxygen and nutrients to the brain is either blocked by a blood clot or bleeds. When that happens, part of the brain cannot get the blood, oxygen, and nutrients it needs, so the brain cells in that region may suffer permanent damage.


The brain is an extremely complex organ that controls thinking, movement, and sensation. If a stroke occurs and blood flow can't reach the region that controls a particular body function, that part of the body won't work as it should.

Because the different areas of the brain all control specific functions, a stroke can cause any physical or cognitive (thinking) problems.

Most of the time, your medical team can effectively diagnose a stroke. The next step is urgent stabilization of your medical condition and stroke treatment to minimize any damage from the stroke.

Why It's Important to Figure out the Cause

A stroke can be caused either by a blood clot blocking the flow of blood to the brain (called an ischemic stroke) or by bleeding of a blood vessel (called a hemorrhagic stroke). A TIA (transient ischemic attack), or “mini-stroke”, is caused by a temporary blood clot that resolves and does not cause permanent damage.

If you have a TIA or an ischemic stroke, the potential causes are somewhat different than the causes of a hemorrhagic stroke. The reason that your medical team works so hard to search for and identify the cause of your stroke is that your stroke risk can often be controlled and managed, substantially reducing your chances of having another stroke.

A stroke typically occurs as the result of years of buildup of disease in the blood vessels of the heart or the brain. Most people who experience a stroke are at high risk of having another stroke. Having one stroke causes a handicap, and having another stroke adds another handicap, which can significantly interfere with your daily life.

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How Your Medical Team Searches for the Cause

If you have had a stroke, you can expect a number of medical tests that examine the structure of your brain to see exactly where the stroke is located and what type of stroke it is. These tests include brain imaging tests, such as Brain MRI, Brain CT, Brain MRA, and Brain MRV. It is unlikely that you would need to have all of these imaging tests, because one test may give enough answers so that other tests are not needed.

When it comes to searching for the underlying cause of your stroke, your healthcare provider may order any of a number of blood tests that examine your heart, your blood clotting tendency, your vitamin B12 level, and even your thyroid function. Again, you would not need to have all of these tests. Your healthcare provider will decide which tests to order depending on your medical history, your family history, the type of stroke you had and the results of preliminary tests.

There are also some lifestyle factors that can add to your risk of strokes, such as smoking, a high-fat diet, major stress and mood problems and lack of physical exercise. Less common causes of stroke include pregnancy or the use of birth control pills. Post-menopausal hormone therapy may pose special stroke risks for women and the use of testosterone therapy for men may increase the risk of stroke.

A Word From Verywell

If you have been told that you have had a cryptogenic stroke, you might be concerned about your health. However, rest assured that the process of searching for causes after a cryptogenic stroke generally uncovers previously unnoticed health problems — ultimately resulting in better health when those problems are addressed and managed.

As you recover from your stroke, you may need one or more types of rehabilitation programs. You should also learn as much as you can about stroke prevention so that you can make the lifestyle changes necessary to prevent yourself from experiencing another stroke.

— Update: 18-03-2023 — found an additional article The heart of cryptogenic strokes: Diagnosing strokes when the cause is unknown from the website for the keyword symptoms of cryptogenic stroke.

Symptoms of cryptogenic stroke

A stroke occurs when a vessel supplying blood to part of the brain is suddenly blocked, killing brain tissue. When you suspect a stroke, immediately call 911. Faster treatment means better long-term outcomes. 

Recognizing the symptoms of stroke is key: 

  • Sudden numbness or weakness of the face, arm or leg

  • Sudden trouble seeing

  • Sudden trouble speaking

  • Extreme headache out of nowhere

  • Sudden loss of balance or trouble walking

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Immediate treatment is focused on restoring blood flow. Treatment may involve the use of clot-busting medications or a procedure to physically remove the blockage. 

How strokes happen

Once someone is stable, our focus turns to rehabilitation preventing additional strokes. Often, a patient’s first question is, “Why did this happen?” Finding the stroke cause is crucial to determine the risk of recurrence and the best prevention. 

So, why did the vessel become blocked in the first place?

Four common stroke causes:

  1. Large-artery problems: Plaque buildup and narrowing of the large arteries in the head and neck. This is usually due to high blood pressure, high cholesterol, diabetes or other risk factors.

  2. Small-vessel problems: Damage to smaller blood vessels deep in the brain. This is also usually due to risk factors such as high blood pressure, high cholesterol or diabetes.

  3. Cardiac source: Clots from the heart travel to and block vessels in the brain, causing stroke. Most commonly a heart rhythm problem (atrial fibrillation) but potentially due to other heart conditions such as heart failure or heart valve problems

  4. Stroke of other determined cause: Less common but well recognized causes such as vasculitis (vessel inflammation), dissection (physical tear in a vessel) or clotting disorders.

How stroke is diagnosed

The initial workup for stroke is aimed at identifying the most likely reason for a blocked vessel. First, we look at the vessels (CT or MRI) to check for major narrowing. We also check for stroke risk factors (high blood pressure, cholesterol, diabetes) and assess the heart for structural problems or abnormal rhythms. 

After this initial workup, up to 30% of strokes do not fit neatly into one of the four categories above. Strokes without a known cause are called “cryptogenic” strokes. 

Types of cryptogenic strokes

Not knowing the cause of a stroke can be extremely frustrating. In cases of cryptogenic stroke, an even more detailed workup is required.

Cryptogenic strokes may be caused by:

  • Atrial fibrillation or afib
  • Patent foramen ovale (PFO)
  • Clotting disorders
  • Aortic arch atheroma

Other rare causes of cryptogenic stroke include cancer, heart valve disease and other types of heart disease.

Atrial fibrillation (Afib)

Atrial fibrillation (Afib) is an irregular and often very fast heart rhythm. Afib occurs when the upper chambers of the heart beat irregularly. This causes blood to pump inefficiently, and clots can form within the left atria. A blood clot can then travel out of the heart to the brain and cause a stroke. 

Symptoms of Afib can include

  • Heart palpitations (hard, fast or irregular heartbeats)
  • Lack of energy/fatigue 
  • Shortness of breath

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However, some patients have no symptoms, making detection difficult. To complicate matters further, patients may only have Afib for a short time, followed by normal heart rhythm. One snapshot in time might not tell the whole story. 

In these cases, prolonged heart monitoring may be useful. Some monitoring devices can be placed under the skin on the chest and monitor the heart rhythm 24 hours a day. If the device detects atrial fibrillation, patients are notified immediately. Your doctor may then suggest stronger blood-thinning medicine to prevent strokes. Some implanted heart monitors can be left in place for up to three years. 

Patent foramen ovale (PFO)

Patent foramen ovale (PFO) is a small opening between the two upper heart chambers that never closed after birth. About 25% of adults have a PFO. Most people with a PFO are completely asymptomatic and never require any type of treatment.

In rare cases, however, a PFO may allow a blood clot to travel to the brain, causing a stroke. Although rare, this is possible in younger people without another explanation for a stroke.

Depending on age and other factors, your doctor may close the PFO to prevent additional strokes. PFO closure is a minimally invasive procedure performed through a small catheter inserted into a leg vein.

Clotting disorders 

A clotting disorder is a condition where a person’s blood has an increased tendency to form clots. There are many different types of clotting disorders. Some are inherited and others are acquired later in life without a family history. If a person tends to form clots, those clots can travel to the brain and cause stroke. Depending on age and family history, additional labs may identify the underlying clotting disorder.

Aortic arch atheroma 

An aortic arch atheroma is a build of plaque within the aorta, the largest artery in the body. The specific part of the aorta that comes off the heart is called the aortic arch. When plaque builds up within the aortic arch, pieces can break off and travel downstream, potentially blocking vessels in the brain and causing a stroke. The same risk factors for plaque buildup in the carotid arteries apply to risk of plaque formation in the aorta.

Treating strokes where the cause is unknown

If you or a loved one has had a stroke, talk to your doctor about the potential causes. Your doctor can perform additional workups to get to the underlying issue. Regardless of the cause, it is also important to address any other contributing factors such as high blood pressure, cholesterol, diabetes and tobacco use. By knowing these potential causes of stroke, working with your doctor can dramatically reduce the risk of having another stroke.


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About the Author: Tung Chi