The two main types of stroke are ischemic stroke, caused by a blocked blood vessel in the brain, and hemorrhagic stroke, caused by a burst blood vessel that bleeds into the brain. About 87% of all strokes are ischemic, making them far more common. Hemorrhagic strokes account for the remaining 13% but tend to be more severe and deadly.
Ischemic Stroke: A Blocked Blood Vessel
An ischemic stroke happens when a blood vessel supplying the brain gets blocked, cutting off oxygen to brain tissue. The blockage typically occurs in one of two ways. A clot can form directly inside a brain artery, usually at a spot narrowed by fatty plaque buildup. Or a clot can form somewhere else in the body, break loose, and travel through the bloodstream until it lodges in a smaller brain artery. This second type is called an embolic stroke.
Clots that travel to the brain often originate in the heart. Conditions like atrial fibrillation (an irregular heartbeat), heart valve disease, and weakened heart muscle all create environments where blood pools and clots form more easily. Clots can also break off from plaque in the carotid arteries, the large vessels running up each side of the neck.
In roughly 30% of ischemic strokes, no clear cause is found even after thorough testing. These are called cryptogenic strokes, and they’re a major focus of ongoing investigation because identifying hidden causes (like an undiagnosed heart rhythm problem) can prevent a second stroke.
Hemorrhagic Stroke: A Burst Blood Vessel
A hemorrhagic stroke happens when a weakened blood vessel in or around the brain ruptures. Blood spills into surrounding tissue, damaging cells both directly and by increasing pressure inside the skull. There are two subtypes based on where the bleeding occurs.
An intracerebral hemorrhage is bleeding within the brain itself. This is the more common form of hemorrhagic stroke and is frequently linked to long-standing high blood pressure, which gradually weakens small arteries deep in the brain until one gives way.
A subarachnoid hemorrhage is bleeding in the space between the brain and the thin layers of tissue covering it. This type is often caused by a ruptured aneurysm, a balloon-like bulge that develops at a weak point in an artery wall. Aneurysms typically form where arteries branch and are subjected to constant blood pressure. They enlarge slowly over time, growing weaker as they stretch. Another less common cause is an arteriovenous malformation (AVM), an abnormal tangle of blood vessels that bypasses normal brain tissue. The walls of these vessels dilate under high-pressure arterial blood flow and can eventually burst.
How Severity Compares
Hemorrhagic strokes are significantly more dangerous in the short term. Within seven days of the stroke, about 13% of hemorrhagic stroke patients die compared to roughly 2% of ischemic stroke patients. At 30 days, the gap remains stark: nearly 20% mortality for hemorrhagic strokes versus about 5% for ischemic strokes. By 90 days, one in four hemorrhagic stroke patients has died, compared to about one in ten with ischemic stroke. The higher death rate reflects the added damage from bleeding and the rapid buildup of pressure inside the skull.
Shared and Unique Risk Factors
High blood pressure is the single biggest risk factor for both types of stroke. Diabetes and high cholesterol also raise the risk across the board. Beyond these shared factors, the two types diverge.
Ischemic strokes are more closely tied to conditions that promote clot formation: atrial fibrillation, coronary heart disease, carotid artery disease, and high cholesterol leading to plaque buildup. Hemorrhagic strokes, on the other hand, are more closely linked to structural problems in blood vessels like aneurysms and AVMs, along with the use of blood-thinning medications that make bleeding harder to stop once it starts.
Treatment Differs by Type
Because the two stroke types have opposite underlying problems, their treatments are fundamentally different. Giving the wrong treatment can be fatal, which is why brain imaging is the very first step in any stroke evaluation.
For ischemic strokes, the priority is restoring blood flow. A clot-dissolving medication can be given intravenously within 4.5 hours of symptom onset. For strokes caused by a large clot in a major brain artery, a procedure called mechanical thrombectomy physically removes the clot using a catheter threaded through the blood vessels. This procedure has been shown to work even up to 24 hours after symptoms begin in carefully selected patients.
For hemorrhagic strokes, the goals are stopping the bleeding and reducing pressure on the brain. Blood pressure is lowered quickly and carefully, because smooth, sustained control helps prevent the bleeding from expanding. If the patient was taking blood thinners, their effects need to be reversed immediately. In some cases, surgery is needed to drain the accumulated blood, particularly for bleeding in the cerebellum (the lower back part of the brain) when the blood collection is large enough to compress the brainstem or block normal fluid drainage.
What About a “Mini-Stroke”?
A transient ischemic attack, commonly called a TIA or mini-stroke, is closely related to ischemic stroke. It happens when blood flow to the brain is temporarily interrupted, causing stroke-like symptoms that resolve on their own. The outdated definition set a 24-hour time limit for symptoms, but that threshold has been replaced. The current medical definition focuses on whether any lasting brain damage occurred, regardless of how long symptoms lasted, because up to one-third of people whose symptoms resolve within 24 hours actually have permanent brain injury visible on imaging.
A TIA is not a harmless event. It’s a warning that the conditions for a full ischemic stroke are in place. People who experience one face a substantially elevated risk of having a complete stroke in the days and weeks that follow, making urgent evaluation and treatment critical.