Mini strokes, known medically as transient ischemic attacks (TIAs), happen when blood flow to part of the brain is temporarily blocked. The blockage usually comes from a blood clot or a piece of fatty plaque that briefly lodges in a brain artery, then breaks up or moves on before causing permanent damage. Unlike a full stroke, a TIA doesn’t destroy brain tissue, but it’s a serious warning sign: roughly 16 out of every 100 people who have a TIA will have a stroke within the following 90 days.
How a Mini Stroke Happens
Your brain needs a constant supply of oxygen-rich blood. When something interrupts that supply, even briefly, brain cells in the affected area stop working normally. That’s what produces the sudden symptoms of a TIA: numbness or weakness on one side of your body, slurred speech, confusion, trouble seeing, or loss of balance. Most of these symptoms appear suddenly and resolve within an hour, though they can last up to 24 hours.
The key difference between a TIA and a full ischemic stroke is what happens to the brain tissue. In a TIA, the blockage clears quickly enough that no permanent injury occurs. Brain imaging after a TIA most commonly shows a normal scan with no signs of damage. When imaging does reveal a small area of injury, doctors may reclassify the event as a minor stroke rather than a TIA.
Atherosclerosis and Carotid Artery Disease
The most common cause of mini strokes is atherosclerosis, the gradual buildup of fatty deposits (plaques) inside artery walls. Plaques are clumps of cholesterol, fat, and blood cells that accumulate over years, slowly narrowing the artery. When plaques form in the carotid arteries, the two large blood vessels on either side of your neck that supply your brain, the risk of a TIA rises significantly.
These plaques cause mini strokes in two ways. First, a plaque can grow large enough to severely narrow the artery, reducing blood flow to the brain. Second, and more commonly, a piece of plaque can break off and travel upstream into a smaller brain artery, temporarily plugging it. Blood clots also tend to form on the rough, damaged surface of a plaque, and those clots can break loose and do the same thing.
Atrial Fibrillation and Heart-Related Clots
Atrial fibrillation (AFib), an irregular and often rapid heart rhythm, is one of the most important causes of TIAs. When the heart’s upper chambers quiver instead of contracting normally, blood doesn’t flow through them efficiently. It pools and slows down, especially in a small pouch called the left atrial appendage. Slow-moving blood is far more likely to clot.
If one of those clots escapes the heart, it travels through the bloodstream and can lodge in an artery feeding the brain. When the clot is small or breaks apart quickly, the result is a TIA rather than a permanent stroke. AFib creates the perfect conditions for clot formation: stagnant blood, damage to the inner lining of the heart, and activation of the body’s clotting system. This combination is why people with AFib are often prescribed blood-thinning medications.
Small Vessel Disease in the Brain
Not all mini strokes originate from large arteries or the heart. Some are caused by disease in the brain’s tiniest blood vessels, the small arteries, arterioles, and capillaries deep inside the brain. This condition, called cerebral small vessel disease, is driven primarily by aging and high blood pressure. Over time, these forces damage the inner lining of small vessels, making them stiff, leaky, and prone to blockage.
The damage follows a progression. Early on, the vessel lining becomes dysfunctional, allowing fluid and harmful proteins to seep into surrounding brain tissue. This disrupts the vessel’s ability to regulate blood flow and damages nearby cells. Eventually, tiny blockages called lacunar infarcts can form, either from the general thickening and hardening of vessel walls or from small fatty deposits at the point where a tiny artery branches off a larger one. Small vessel disease tends to accumulate silently over years and is a major contributor to TIAs in older adults.
Blood Pressure and the Risk Window
High blood pressure is the single most important modifiable risk factor for mini strokes. It damages artery walls throughout the body, accelerates plaque buildup, and worsens small vessel disease in the brain. For people who have already had a TIA or stroke, keeping systolic blood pressure (the top number) below 130 mmHg significantly lowers the chance of another event, reducing the risk of a recurrent stroke or TIA by about 23% compared to those whose pressure stays above 140.
Interestingly, blood pressure that drops too low also carries risk. People with systolic readings below 105 mmHg after a stroke or TIA have roughly double the mortality rate compared to those above 140. The safest range for preventing repeat events appears to be between 105 and 130 mmHg, a target that balances protection against future strokes with adequate blood flow to the brain and other organs.
Less Common Causes
In younger adults, mini strokes sometimes have causes that have nothing to do with the typical buildup of plaque or high blood pressure.
Artery dissection. A tear in the inner wall of an artery in the neck (carotid or vertebral artery) allows blood to seep into the artery wall, creating a bulge that narrows or blocks the vessel. This accounts for up to 25% of strokes and TIAs in young and middle-aged adults. Dissections can happen spontaneously, or they can be triggered by neck manipulation, sports injuries, or trauma. The blockage itself isn’t usually what causes the brain event. Instead, clots form at the site of the tear and then break off and travel to the brain.
Blood vessel inflammation. Vasculitis, inflammation of blood vessel walls, can narrow or block arteries supplying the brain. It may stem from autoimmune conditions or infections including herpes zoster, HIV, and syphilis. Giant cell arteritis, the most common form affecting the brain’s medium and large arteries, occurs at a rate of 7 to 18 cases per 100,000 people and primarily affects adults over 50. Primary inflammation confined to the central nervous system is much rarer, estimated at only about 0.24 cases per 100,000 people per year.
Why a TIA Is a Medical Emergency
Because TIA symptoms resolve on their own, it’s tempting to brush them off. That’s dangerous. A TIA is the clearest warning the body gives before a full stroke. The risk of a major stroke is highest in the first few days after a TIA, making rapid evaluation critical. Identifying the underlying cause, whether it’s a narrowed carotid artery, undiagnosed AFib, or dangerously high blood pressure, allows treatment to begin before permanent brain damage occurs.
The symptoms to watch for follow the well-known FAST pattern: facial drooping, arm weakness, speech difficulty, and time to call emergency services. Additional signs include sudden vision problems in one or both eyes, dizziness, loss of coordination, and confusion. Even if these symptoms vanish completely within minutes, they still warrant emergency evaluation.