ANTHONY MUNSON, M.D.
NEUROLOGIST, MEDICAL DIRECTOR,
CHRISTIANA CARE STROKE PROGRAM
What is Stroke?
The brain is responsible for coordinating how we move, think, speak, hear, see, feel, and behave. To function properly, brain cells must have a continuous supply of oxygen and other nutrients from the blood. When the blood supply is disrupted, even for a few minutes, areas of the brain may be damaged and a person may suddenly lose some of the functions controlled by that region of the brain. This sudden loss of function is referred to as a stroke.
Blood is continuously pumped from the heart to the brain via several artery groups. Within the brain, these arteries branch into smaller and smaller arteries and then into tiny thin-walled vessels (called capillaries) which supply the oxygen and nutrients that the brain tissue needs. It is when this continuous blood supply is disrupted that brain cells die and a stroke results.
A stroke is the result of a sudden blockage caused by a clot, narrowing of an artery, or bursting of a blood vessel. It is this distinction that defines the main types of stroke. The two main kinds of strokes are known as ischemic and hemorrhagic.
Ischemic is the most common type of stroke and constitutes an estimated 80 percent of all strokes. An ischemic stroke results when a blood vessel leading to the brain becomes blocked. This type of stroke may occur for three main reasons:
1.) A blood clot (or thrombus) forms inside an artery in the brain, blocking the flow of blood. Referred to as thrombotic stroke, this is the most common type of ischemic stroke. Blood clots form most often in arteries damaged by atherosclerosis, a disease in which rough fatty deposits, or plaque, build up on the walls of the artery. These deposits can crack and expose substances that induce clots to form.
2.) A clot forms in the blood, but unlike thrombotic stroke, it originates somewhere other than the brain. This type of stroke is referred to as an embolic stroke and occurs when a piece of clot (an embolus) or plaque fragment breaks loose and is carried in the bloodstream to the brain. An embolus can form in many places in the body, including the heart and the arteries of the neck that transport blood to the brain. The embolus travels through the arteries, which branch off into smaller vessels. When it reaches a point where it can go no further, it plugs the vessel and cuts off the blood supply to the area of the brain that is supplied by that vessel.
Note: Both thrombotic and embolic strokes are referred to as ischemic because the blood supply has been blocked to the brain area. You may hear of the term cerebral infarction in connection with thrombotic and embolic types of stroke. Cerebral refers to the brain. An infarct is an area of tissue death due to a blockage of blood flows, such as a blood clot. It is also a result of ischemia, which refers to an inadequate blood (and therefore oxygen) supply to a certain part of the body.
3.) Blood flow decreases to the brain which can result from poor overall blood flow in the body due to heart damage or dysrhythmia (irregular heart rhythm that makes pumping inefficient or ineffective). This type of ischemic stroke is called hypoperfusion or watershed and is less common than the other two types.
The second main type of stroke is hemorrhagic and occurs when a blood vessel in or around the brain ruptures or leaks. This rupture not only denies the blood from reaching its destination, it also causes a leakage of blood into the brain or the area surrounding the brain. When this happens, the cells nourished by the artery are unable to obtain their normal supply of nutrients and stop functioning properly. Blood begins to accumulate and clot soon after the rupture of the artery, causing a disruption of brain function and potentially increased pressure on the brain itself. Cerebral hemorrhage is most likely to occur in people who suffer from a combination of atherosclerosis and high blood pressure.
Transient Ischemic Attack (TIA)
About one-third of all strokes are preceded by one or more transient ischemic attacks (TIAs) or what are sometimes referred to as “mini-strokes.” TIAs can occur days, weeks, or even months before a stroke and are caused by temporary interruptions in the blood supply to the brain. The symptoms resemble those of a stroke but last a relatively short time and completely resolve.
Because TIAs are temporary, it is easy to ignore them or to believe the problem has disappeared. However, the underlying problem that caused the TIA continues to exist. Therefore, attention must be paid to these symptoms and a TIA should be viewed as early warning of a potentially serious stroke in the future.
If you or someone you know experiences a TIA, it is important to seek the assistance of a health care professional. Call your doctor immediately or go to the closest emergency department, even if the symptoms seem to be getting better or have resolved.