What Is a Stroke?

The term “stroke” usually refers either to a cerebral infarction or to non-traumatic cerebral hemorrhage. Depending on the population you are seeing (ethnicity, age, comorbidities) the ratio of infarcts to hemorrhages is about 4:1. A stroke happens when blood flow to a part of the brain stops. A stroke is sometimes called a “brain attack.”

There are two major types of stroke: ischemic stroke and hemorrhagic stroke.
Ischemic stroke occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot. This may happen in two ways:

• A clot may form in an artery that is already very narrow. This is called a thrombotic stroke.
• A clot may break off from another place in the blood vessels of the brain, or from some other part of the body, and travel up to the brain. This is called cerebral embolism, or an embolic stroke.

Ischemic strokes may be caused by clogged arteries. Fat, cholesterol, and other substances collect on the artery walls, forming a sticky substance called plaque.

A hemorrhagic stroke occurs when a blood vessel in part of the brain becomes weak and bursts open, causing blood to leak into the brain. Some people have defects in the blood vessels of the brain that make this more likely.

There is currently no 100% sensitive and specific test for cerebral infarction in the emergency department, so that the diagnosis is usually made on the basis of a characteristic history, exam, presence of comorbidities, and the absence of seizures or other stroke mimics. CT scanning is usually negative in the first three hours, or shows only subtle signs that have low inter-observer reliability. If available, MR imaging, or detection of an occluded artery by transcranial Doppler or arteriography (by CT, MRI or intra-arterial catheterization), can be confirmatory. Parenchymal or subarachnoid hemorrhage, on the other hand, can be reliably detected by emergent CT scanning.