NYU Langone specialists are experts at identifying the two main types of stroke. Ischemic strokes are caused by a blockage in an artery, while hemorrhagic strokes are caused by bleeding.
An ischemic stroke is the most common type of stroke, accounting for more than 80 percent of all strokes. This type of stroke occurs when the blood supply to the brain is disrupted or severely decreased.
An ischemic stroke may be triggered by a thrombus, a clot that forms in one of the arteries that supplies blood to the brain, or by an embolus, a blood clot that travels through the bloodstream and becomes lodged in a blood vessel in the brain. This can lead to symptoms of a stroke.
A transient ischemic attack, often called a ministroke, is a brief period of stroke-like symptoms similar to a regular stroke, but it’s not likely to cause permanent damage. These symptoms often go away in less than 24 hours. Like an ischemic stroke, this type of stroke occurs when a clot temporarily blocks blood flow to part of the brain.
A transient ischemic attack doesn’t cause lasting symptoms because the blockage is temporary. But it is a serious warning sign of an impending stroke that should not be ignored. About 40 percent of people who have had this type of stroke go on to have an actual stroke, so immediate care is critical.
A hemorrhagic, or bleeding, stroke happens when a blood vessel or vascular lesion—an abnormal collection or formation of blood vessels—in the brain bursts, causing blood to leak into the brain or the space around the brain. This is often due to elevated blood pressure, a brain aneurysm or a vascular malformation.
Hemorrhagic strokes, which can be classified as intracerebral or subarachnoid, are less common than the ischemic type and comprise approximately 15 percent of all strokes.
An intracerebral hemorrhage happens when a blood vessel in the brain bursts and spills into the surrounding tissue, damaging brain cells. Causes include high blood pressure, trauma, vascular malformations, or the use of blood-thinning medications.
A subarachnoid hemorrhage occurs when an artery on or near the surface of the brain bursts and spills into the area around the brain called the subarachnoid space. This bleeding is often signaled by a sudden, severe headache.
A common cause of a subarachnoid hemorrhage is the bursting of a small, sack-shaped pouch on an artery, called an aneurysm. After the hemorrhage, the blood can irritate the brain and cause the vessels in the brain to narrow or go into spasm, limiting blood flow and putting the brain at risk for stroke. This condition is called a cerebral vasospasm.
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