There are three main types of stroke: ischemic (caused by a blocked blood vessel), hemorrhagic (caused by bleeding in or around the brain), and transient ischemic attack, often called a “mini-stroke.” About 87% of all strokes are ischemic, while roughly 13% are hemorrhagic. Within each category, there are important subtypes that differ in cause, severity, and treatment.
Ischemic Stroke
An ischemic stroke happens when a blood clot or buildup of fatty deposits blocks an artery supplying the brain. Without blood flow, brain cells start dying within minutes. There are two main ways this blockage occurs.
In a thrombotic stroke, the clot forms directly inside an artery in or leading to the brain. This usually develops where fatty plaque has already narrowed the vessel wall over time. People with high blood pressure, high cholesterol, or diabetes are especially vulnerable. Thrombotic strokes can affect large arteries (causing widespread damage) or tiny deep vessels in the brain, producing what are called lacunar strokes, small infarcts typically less than 1.5 centimeters across.
In an embolic stroke, the clot forms somewhere else in the body, usually the heart, and travels through the bloodstream until it lodges in a brain artery. Atrial fibrillation, an irregular heart rhythm, is one of the most common sources. Because the clot can travel to any part of the brain, embolic strokes often strike suddenly and without warning.
About one in six ischemic strokes can’t be traced to a clear cause even after thorough testing. These are classified as cryptogenic strokes. In many of these cases, the pattern on brain imaging suggests an embolism, but doctors can’t identify where it came from. Undetected atrial fibrillation is a leading suspect, which is why extended heart monitoring (often for days or weeks) is part of the workup.
Hemorrhagic Stroke
A hemorrhagic stroke occurs when a blood vessel in or around the brain ruptures, spilling blood into surrounding tissue. The bleeding damages brain cells directly, and the pooling blood creates pressure that can injure nearby areas. Though hemorrhagic strokes account for only about 13% of all strokes, they tend to be more deadly than ischemic strokes.
Intracerebral Hemorrhage
This is bleeding that happens inside the brain itself. The most common cause is long-standing high blood pressure, which weakens small arteries over years until one finally gives way. Other triggers include abnormal tangles of blood vessels (known as arteriovenous malformations, or AVMs), which contain weakened vessels that dilate over time and can eventually burst under the pressure of blood flow. Ruptured brain aneurysms, blood-thinning medications, and cocaine use can also cause intracerebral bleeding.
Subarachnoid Hemorrhage
In a subarachnoid hemorrhage, blood leaks into the space between the brain and the thin tissue layers covering it. This type is most often caused by a ruptured aneurysm, a bulging weak spot in an artery wall. High blood pressure and smoking are major risk factors. In some cases, a sudden spike in blood pressure from strenuous activity or intense emotion can trigger the rupture. Certain medications, including stimulant-based diet pills and amphetamines, can also cause an aneurysm to bleed.
The hallmark symptom of a subarachnoid hemorrhage is often described as the worst headache of your life, a sudden, explosive pain unlike anything experienced before. This type of stroke is a medical emergency that frequently requires surgical intervention.
Transient Ischemic Attack (TIA)
A TIA produces stroke-like symptoms, such as sudden weakness, slurred speech, or vision loss, but they resolve on their own, typically within minutes to an hour. Unlike a full stroke, a TIA doesn’t cause permanent brain damage. It happens when blood flow to part of the brain is temporarily interrupted, usually by a small clot that dissolves quickly.
Despite the short duration of symptoms, a TIA is a serious warning. The 90-day stroke risk after a TIA can be as high as 17.8%, and nearly half of those strokes happen within the first two days. Treating a TIA as an emergency, with rapid evaluation and treatment of underlying risk factors, dramatically lowers the chance of a full stroke following it.
Watershed Stroke
Watershed strokes are a less commonly discussed but important subtype. They occur in the “border zones” of the brain where the outermost branches of two separate arteries meet. These areas sit at the far end of each artery’s supply line, making them especially vulnerable when blood pressure drops.
A classic scenario involves someone who already has significant narrowing in a carotid artery (the major artery in the neck feeding the brain) and then experiences a sudden drop in blood pressure from cardiac surgery, severe blood loss, or another cause. The areas farthest downstream lose flow first. Symptoms can include episodic, fluctuating weakness in the hand or arm, sometimes with involuntary shaking of the upper limb. Fainting at the onset of symptoms is another telltale sign. Recent research suggests that tiny clots from unstable plaque in a narrowed carotid artery may combine with low blood flow to make these strokes more likely, rather than low pressure alone being responsible.
Silent Strokes
Not all strokes announce themselves with dramatic symptoms. Silent brain infarcts are small areas of stroke damage that show up on brain imaging but never caused noticeable symptoms at the time they occurred. They’re surprisingly common: more than 20% of people in their 70s have evidence of at least one on a brain scan, and that number rises to 35% in adults over 85.
Silent strokes matter because they’re not truly harmless. Each one destroys a small amount of brain tissue, and the damage accumulates over time. People with multiple silent infarcts face a higher risk of cognitive decline and dementia. They’re also at greater risk for future symptomatic strokes. Silent strokes share the same risk factors as visible strokes: high blood pressure, diabetes, smoking, and atrial fibrillation.
Stroke in Children
Stroke is rare in children but not nonexistent. Neonatal stroke occurs in roughly 1 in 4,000 live births per year. In newborns, the cause often remains undetermined, but contributing factors include cardiac disorders, infections, and blood clotting abnormalities. Fewer than 5% are linked to birth asphyxia.
In older children, ischemic stroke is more common than hemorrhagic. Risk factors include congenital heart disease, sickle cell disease, infections (up to 30% of childhood strokes are linked to a prior chickenpox infection that damages blood vessel walls), and a condition called moyamoya, where arteries at the base of the brain progressively narrow. When children do have hemorrhagic strokes, the most common cause is an arteriovenous malformation.
Treatment Windows Differ by Type
The type of stroke determines the treatment, and timing is critical. For ischemic strokes, clot-dissolving medication can be given within 4.5 hours of symptom onset. For strokes caused by blockages in large brain arteries, a procedure to physically remove the clot can be effective up to 24 hours after symptoms begin in carefully selected patients, though the best outcomes come with faster treatment.
Hemorrhagic strokes require the opposite approach. Clot-dissolving drugs would make bleeding worse, so treatment focuses on controlling blood pressure, stopping the bleed, and relieving pressure on the brain. This is one reason why brain imaging is performed immediately when someone arrives at the hospital with stroke symptoms: the treatment for one type would be dangerous for the other.