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.” Globally, ischemic strokes account for about 65% of all strokes, intracerebral hemorrhages make up roughly 29%, and subarachnoid hemorrhages account for about 6%. Within each category, though, there are important subtypes that differ in their causes, severity, and treatment.
Ischemic Stroke
An ischemic stroke happens when a blood clot or other blockage cuts off blood flow to part of the brain. Without oxygen, brain cells in the affected area begin to die within minutes. This is the most common type of stroke by a wide margin.
There are two main ways an ischemic stroke develops. In a thrombotic stroke, a clot forms directly inside an artery that supplies the brain. This usually happens at a spot where fatty plaque has built up on the artery wall, eventually becoming unstable and rupturing. The body’s clotting system rushes to the site, and the resulting clot can partially or fully block blood flow. In an embolic stroke, the clot forms somewhere else in the body, typically the heart, and travels through the bloodstream until it lodges in a narrower brain artery. About one-third of ischemic strokes originate from clots that formed in the heart, especially in people with atrial fibrillation, an irregular heart rhythm that lets blood pool and clot.
Lacunar Stroke
A lacunar stroke is a specific subtype of ischemic stroke that affects the tiny arteries deep inside the brain. These strokes produce small areas of damage, less than 20 mm across, in structures like the internal capsule or the brainstem. The name comes from the Latin word for “hole,” describing the small cavity left behind after the damaged tissue breaks down. Lacunar strokes are strongly linked to chronic high blood pressure, which gradually damages these small vessels over years. Symptoms often involve isolated problems like weakness on one side of the face and arm, or difficulty with coordination, rather than the broader combination of symptoms seen in larger strokes.
Cryptogenic Stroke
In roughly one out of every six ischemic strokes, doctors can’t identify a clear cause even after thorough testing. These are called cryptogenic strokes. A more specific term, embolic stroke of undetermined source (ESUS), is used when imaging confirms the stroke pattern looks embolic but no source of the clot can be found. To qualify, doctors must rule out significant artery narrowing, major heart conditions, and other known causes like artery tears. Extended heart monitoring for at least 24 hours is part of the minimum workup, since brief episodes of atrial fibrillation can be easy to miss.
Hemorrhagic Stroke
Hemorrhagic strokes happen when a blood vessel in or around the brain ruptures, spilling blood into surrounding tissue. The bleeding itself damages brain cells, and the pooling blood creates pressure that can harm nearby areas as well. Although less common than ischemic strokes, hemorrhagic strokes tend to be more deadly.
Intracerebral Hemorrhage
This type involves bleeding directly within the brain tissue. The most common cause is long-standing high blood pressure, which weakens the walls of small arteries deep in the brain until one eventually bursts. Symptoms depend on the size and location of the bleed but often include sudden severe headache, weakness, and altered consciousness. Intracerebral hemorrhage accounts for about 29% of all strokes worldwide, making it the second most common type overall.
Subarachnoid Hemorrhage
In a subarachnoid hemorrhage, bleeding occurs in the space between the brain and the thin membranes that surround it. The most frequent cause is a ruptured aneurysm, a weak, balloon-like bulge in an artery wall that gives way under pressure. Arteriovenous malformations (abnormal tangles of blood vessels) and head trauma can also cause this type. A subarachnoid hemorrhage often announces itself with what people describe as the worst headache of their life, sudden and explosive. It accounts for roughly 6% of strokes but carries a high rate of serious complications.
Transient Ischemic Attack
A transient ischemic attack (TIA) produces stroke-like symptoms that resolve completely, usually within minutes to a couple of hours. It was once defined simply by symptoms lasting less than 24 hours, but the American Heart Association updated the definition in 2009. A TIA now means symptoms have resolved and brain imaging shows no evidence of permanent damage. If imaging reveals even a small area of dead tissue, it’s reclassified as an ischemic stroke regardless of how quickly symptoms cleared.
TIAs are a serious warning sign. The same mechanisms that cause full ischemic strokes, clots from plaque buildup or the heart, cause TIAs. The difference is that the blockage clears on its own before lasting damage occurs. Without treatment of the underlying cause, the risk of a full stroke in the days and weeks following a TIA is significant.
Silent Stroke
Not all strokes produce noticeable symptoms. Silent strokes destroy small clusters of brain cells in areas that don’t control obvious functions like movement or speech, so the person has no idea anything happened. The damage only shows up if a brain scan is done for another reason. One silent stroke may cause no detectable change, but they tend to recur. Over time, the accumulated damage erodes memory and thinking ability. Research has shown that people with silent brain infarcts perform worse on memory and cognitive tests, and this decline occurs independently of the brain shrinkage typically associated with Alzheimer’s disease. The more silent strokes a person has experienced, the harder it becomes for the brain to compensate.
Stroke in Children
Strokes are rare in children, but they do happen, and the causes often differ from those in adults. Congenital heart problems, such as abnormal valves, can allow clots to form in the heart and travel to the brain. Sickle cell disease is one of the most significant risk factors: at least 10% of children with sickle cell disease will have a stroke. The misshapen red blood cells can’t deliver oxygen efficiently, and blood vessels leading to the brain may narrow or close off entirely. Annual screening with a painless ultrasound of the brain’s blood vessels is recommended for children with sickle cell disease between ages 2 and 16, and regular blood transfusions in high-risk children can reduce stroke risk by more than 90%.
Hemorrhagic strokes in children are most often caused by arteriovenous malformations, while conditions affecting clotting, like hemophilia, also raise the risk of bleeding in the brain.
Recognizing Stroke Symptoms
Regardless of type, strokes share a set of warning signs captured by the acronym BE FAST:
- Balance: sudden loss of balance or coordination
- Eyes: vision changes, including loss of sight in one or both eyes or double vision
- Face: drooping on one side of the face
- Arms: weakness in an arm or leg, usually on one side
- Speech: slurred words or difficulty understanding others
- Time: call emergency services immediately
Time matters enormously because treatment options narrow quickly. For ischemic strokes, clot-dissolving medication is most effective within 4.5 hours of symptom onset. A procedure to physically remove a large clot can sometimes be performed up to 24 hours later in select patients, but outcomes are better the sooner blood flow is restored. Hemorrhagic strokes require a completely different approach focused on controlling the bleeding and reducing pressure in the skull, which is one reason getting an accurate diagnosis through brain imaging as fast as possible is critical.