The two 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 or around the brain. Ischemic strokes account for about 87% of all strokes, making them far more common. Hemorrhagic strokes make up the remaining 13% but are significantly more deadly in the short term.
Ischemic Stroke: A Blocked Blood Vessel
An ischemic stroke happens when a blood vessel supplying the brain becomes blocked, cutting off oxygen to brain tissue. The blockage typically occurs in one of two ways. In the first, a clot forms directly inside a brain artery that has narrowed over time from fatty plaque buildup. This tends to develop in spots where arteries branch or curve, since those areas are more prone to plaque accumulation.
In the second and more common mechanism, a clot forms somewhere else in the body and travels to the brain, where it lodges in a smaller vessel. These traveling clots most often originate in the heart. Atrial fibrillation, an irregular heart rhythm, is one of the biggest culprits. People with atrial fibrillation face a three- to five-fold higher risk of stroke because blood can pool and clot in the heart’s upper chambers. Clots can also form on damaged heart valves, in weakened sections of the heart wall after a heart attack, or in arteries of the neck and aorta.
Less commonly, a clot forms in a vein elsewhere in the body and reaches the brain through a small hole in the heart called a patent foramen ovale. This opening exists in everyone before birth but usually closes. When it doesn’t, it can serve as a pathway for venous clots to cross into arterial circulation and travel to the brain.
Hemorrhagic Stroke: A Burst Blood Vessel
A hemorrhagic stroke occurs when a weakened blood vessel ruptures and bleeds into or around brain tissue. There are two subtypes, distinguished by where the bleeding happens.
An intracerebral hemorrhage is bleeding directly inside the brain tissue itself. High blood pressure is the primary driver. Over years, uncontrolled hypertension damages the walls of small arteries in the brain, making them fragile and prone to rupture. When one gives way, blood spills into surrounding brain tissue, creating pressure that damages cells.
A subarachnoid hemorrhage is bleeding in the space between the brain and the thin membrane that surrounds it. Most subarachnoid hemorrhages result from a ruptured brain aneurysm, a balloon-like bulge in an artery wall that can weaken and burst. Blood floods the surface of the brain rather than penetrating deep into the tissue, but the effect is still devastating. It often causes a sudden, severe headache commonly described as the worst headache of a person’s life.
How Symptoms Overlap and Differ
Both stroke types share core warning signs: sudden numbness or weakness on one side of the body, difficulty speaking or understanding speech, vision changes, trouble walking or loss of coordination, and a sudden severe headache. The acronym FAST (Face drooping, Arm weakness, Speech difficulty, Time to call emergency services) applies to both types.
In practice, symptoms alone cannot reliably distinguish one type from the other. Hemorrhagic strokes are more likely to involve a sudden explosive headache, vomiting, and rapid loss of consciousness, but these can also occur with large ischemic strokes. This is why brain imaging is essential before any treatment begins.
Why Telling Them Apart Matters Immediately
The treatments for each type are essentially opposite. For an ischemic stroke, the goal is to dissolve or remove the clot to restore blood flow. For a hemorrhagic stroke, the goal is to stop the bleeding and reduce pressure on the brain. Giving a clot-dissolving treatment to someone with a brain bleed would be catastrophic.
A non-contrast CT scan of the head is the first test performed in the emergency department. It’s fast, widely available, and reliably shows whether blood is pooling in or around the brain. If the scan shows bleeding, the stroke is hemorrhagic. If it doesn’t, the working diagnosis is ischemic, and treatment to restore blood flow can begin.
Treatment Windows for Ischemic Stroke
Time is the defining factor in ischemic stroke treatment. A clot-dissolving medication given through an IV works best when administered within 4.5 hours of symptom onset. For people who wake up with stroke symptoms or don’t know exactly when they started, advanced brain imaging can identify whether salvageable tissue remains, potentially extending the treatment window up to 9 hours from the midpoint of sleep.
For strokes caused by a large clot blocking a major brain artery, a procedure called mechanical thrombectomy can physically retrieve the clot using a catheter threaded through the blood vessels. Current guidelines allow this procedure in select patients up to 24 hours after symptom onset, as long as imaging confirms there is still brain tissue worth saving. This extended window has been one of the most significant advances in stroke care, because many patients who previously would have been told it was “too late” now have a treatment option.
Treatment for Hemorrhagic Stroke
Hemorrhagic stroke management focuses on controlling the bleed and protecting the brain from further damage. Blood pressure control is the immediate priority. Guidelines recommend bringing systolic blood pressure below 140 mmHg in the acute phase, though pushing it too low (below 130) has been associated with worse outcomes. The goal is a range that stops the bleeding from expanding without starving the brain of blood flow.
Some patients need surgery to drain accumulated blood and relieve pressure on the brain, particularly when the bleeding is large or continues to expand. Recovery from hemorrhagic stroke tends to be slower initially, but the brain may actually recover more function over time compared to ischemic stroke because the surrounding tissue is compressed rather than permanently destroyed by oxygen deprivation.
Mortality and Recovery Differences
Hemorrhagic strokes are far more lethal in the early days. Within the first week, the death rate for hemorrhagic stroke is about 13%, compared to roughly 2% for ischemic stroke. At 30 days, those figures are approximately 20% and 5%, respectively. By 90 days, about one in four hemorrhagic stroke patients has died, compared to about one in ten with ischemic stroke.
Interestingly, this gap narrows over time. After three months, stroke type no longer predicts mortality. Among survivors, long-term disability appears comparable between the two types when matched for initial severity. The early period is the critical differentiator.
Transient Ischemic Attack: The Warning Stroke
A transient ischemic attack, often called a mini-stroke, produces the same symptoms as an ischemic stroke but resolves on its own, usually within an hour and always within 24 hours. It happens when a clot temporarily blocks blood flow to part of the brain and then dissolves or dislodges before causing permanent damage.
A TIA is a medical emergency, not a minor event. It signals that the conditions for a full stroke are already in place. Without treatment of the underlying cause, whether that’s a narrowed artery, an irregular heart rhythm, or uncontrolled blood pressure, the risk of a major stroke in the following days and weeks is substantial.
Risk Factors by Stroke Type
Many risk factors are shared across both types: high blood pressure, diabetes, smoking, obesity, and age. High blood pressure is the single most important modifiable risk factor for both ischemic and hemorrhagic stroke, though it plays a particularly direct role in hemorrhagic stroke by physically weakening artery walls over time.
Atrial fibrillation is more specifically linked to ischemic stroke, particularly the embolic subtype where clots form in the heart. People with atrial fibrillation are typically prescribed blood-thinning medication to reduce this risk. Newer direct-acting oral anticoagulants are now preferred over older options like warfarin for most patients with this condition.
For hemorrhagic stroke, additional risk factors include brain aneurysms (which may be present from birth or develop over time), excessive alcohol use, and use of blood-thinning medications, which can make any bleeding harder to control. This creates a clinical tension: blood thinners protect against ischemic stroke but can increase the severity of a hemorrhagic one, which is why the decision to prescribe them always involves weighing both risks.