The Science of Stroke

What Is Stroke?

Stroke is the death of brain. Stroke can occur two ways: either a blood vessel to the brain becomes occluded or a blood vessel to the brain bursts.

What Is an Artery?

Arteries are the vessels through which a constant supply of fresh blood is brought to the brain. Think of arteries as the pipes through which blood travels to brain cells. If blood flow is cut off to a particular region of the brain, cells in that region will not be able to carry out their specific task.

What Is the Difference Between a Stroke and a Heart Attack?

Heart attacks kill muscle cells that decrease the ability of the heart to pump blood. When brain cells die they may be unique, resulting in permanent loss of a certain function.

What Type of Equipment Do You Need to Assess Stroke?

Advanced CT scanners are required to determine whether the stroke is caused by a blood clot or a bleed. Upon arrival to the hospital, a CT scan will be performed as quickly as possible, as it is instrumental in helping doctors decide which form of treatment is likely to be most effective. 

What Are the Two Types of Stroke?

Ischemic Stroke (Caused by a Blocked Blood Vessel)

Ischemic stroke occurs when an artery, or pipe to the brain, is blocked or clogged. A constant supply of blood is required to nourish all brain cells. A steady amount of oxygen, glucose (sugar), and other nutrients are required to prevent brain cell death.

CT scan, head.	CT image of a patient with a large, acute stroke.	Angiogram showing blocked brain artery.

Ischemic stroke can occur when deposits of fatty material, calcium, and fibrous tissue form a sticky and hard plaque that can block or narrow the artery. Pieces of plaque that originate in the heart or the arteries in the neck can travel downstream and clog arteries in the brain. This is referred to as embolic ischemic stroke.

MRA (Angiogram) of the blood vessels that feed the brain.

Blocked Blood Vessels in the Brain

• Plaque can also originate in a blood vessel in the brain. This occurs less frequently than embolic stroke (plaque originates in the heart or carotid arteries) and is called thrombotic ischemic stroke.

Hemorrhagic Stroke (Caused by a Broken Blood Vessel)

Hemorrhagic stroke is a bleeding stroke. It occurs when a weakened blood vessel ruptures. Blood leaks out of the burst vessel (pipe) and into surrounding tissue. This is harmful because the leaking blood can damage brain tissue. Hemorrhagic stroke also results in brain cell death.

There are two ways in which a blood vessel may become weakened and eventually rupture. First, a vessel may expand in a way that resembles a balloon filling with water. If the vessel expands too much, it may burst. This is called an aneurysm. Second, blood vessels may form abnormally and become tangled. This is known as an arteriovenous malformation (AVM), and these vessels can also become weak enough to rupture.

Hemorrhagic strokes may be intracerebral or subarachnoid. These terms describe the abnormal location of the bleeding. Intracerebral hemorrhages produce bleeding in the tissue of the brain. In contrast, Subarachnoid hemorrhage spills blood into the spinal fluid that bathes the surface of the brain.

What Is Ischemic Stroke Therapy?

In the case of ischemic stroke, doctors need to act quickly to open the blocked artery as soon as possible, to minimize long-term effects on the patient. 

• This can be done with tissue plasminogen activator (tPA), which is a drug that breaks up blood clots. tPA is given to patients through a vein in their arm (intravenously). The sooner tPA is administered, the more effective it will be.
• A doctor may also use a metal wire device, called a stent retriever, in order to physically unblock an artery. A long flexible tube called a catheter, which contains the stent retriever, is inserted into the patient's upper thigh and threaded all the way up to the arteries in the brain. Then, the device surrounds the blood clot and pulls it out of the blocked blood vessel, restoring regular blood flow. This type of treatment uses the same principle as a plumber, when they unclog a blocked pipe using a drain snake.

What Is a TIA?

• Transient ischemic attack (TIA) is a temporary stroke with symptoms that last less than 24 hours. This is usually because the blood clot eventually dissolves on its own and the artery reopens.
• The severity of TIA depends on the portion of the brain that is denied blood.

Though symptoms may disappear, TIA often indicates that a more severe stroke may occur soon. Warning signs are not to be taken lightly, and patients should still seek treatment if they suspect they are experiencing TIA.