Types of Stroke

The human brain is an astonishingly complex organ, with its approximately 87 billion nerve cells, called neurons, networked and interacting together in dazzling order to give us consciousness, process sensory data, and regulate many of the body’s functions. All of that complicated activity requires a steady supply of blood carrying oxygen and nutrients to the brain through large arteries. As soon as that blood supply is disrupted…that is, as soon as we have a stroke…the cells whose activities govern our consciousness and functions begin to die off. This describes the essence of a stroke in the broadest sense, but the particular ways in which the blood flow is disrupted cause different types of stroke, and what the patient experiences as they have it.

What are the two main types of stroke?

In about 87% of strokes, called ischemic strokes as we mentioned in Chapter 1, the disruption of blood flow to the brain occurs because an artery has become blocked, usually by a blood clot. The arteries where the blockage occurs are typically either the carotid arteries that run along either side of the neck or arteries in the brain itself.

In the other major type of stroke mentioned in the previous chapter, a hemorrhagic stroke, rather than the blood flow being disrupted by a blockage, a vessel ruptures and floods part of the brain with blood. The ruptured artery is either inside the brain or located between the skull and the membrane surrounding the brain. The mass of blood released by the rupture, which is called a hematoma, may disrupt normal circulation in the affected area of the brain, and swelling may also put pressure against the brain, damaging or killing neurons.

Both types of strokes can produce symptoms including loss of balance, blurred vision, facial drooping, weakness in the arms or legs, and speech problems. The onset of a hemorrhagic stroke is often, but certainly not always, felt as a sudden headache.

Each of these two main categories of stroke can be further classified into subtypes.

Ischemic strokes

There are two separate frameworks for categorizing an ischemic stroke. One has to do with where the blockage forms, and the other has to do with the severity and duration of the symptoms.

In terms of location of the blockage, the two types of ischemic strokes are…

• Thrombotic stroke: Roughly half of all ischemic strokes occur when a thrombus (a clot) appears in one of the arteries feeding the brain or in an artery in the brain itself, blocking blood flow. This is normally caused by the narrowing of the arteries and the buildup of plaque known as atherosclerosis. Just as there are two types of ischemic strokes, there are also two types of thrombotic strokes, depending on the size of the artery where the thrombus has formed. Those subtypes are called “large-vessel” and “small-vessel” strokes.
  • A lacunar stroke is a small-vessel stroke in which the thrombus occurs in a narrow artery deep within the brain. Lacunar strokes often cause paralysis on one side of the body, and they may produce numbness, sensory symptoms, and motor defects. They are more prevalent in men than in women.

• Embolic stroke: In this type of ischemic stroke, the blockage forms elsewhere in the body and travels through the blood vessels to the brain. In such a case, the clot is not called a thrombus but an embolism. Stroke-causing embolisms often form in the carotid arteries, in the aorta, or in the heart before traveling to the brain. Embolic strokes may also be caused by blockages other than blood clots, including bits of cholesterol, air bubbles, infectious material, and pieces of calcium.

When classifying an ischemic stroke in terms of the severity and duration of the symptoms, the following categories are used:

• Transient ischemic attack (TIA): In this type of stroke, a blockage occurs only briefly, causing symptoms that only last for a short amount of time. Once the blockage clears, the symptoms go away, leaving no lasting damage. However, TIAs very often precede full-blown strokes, so they must be treated as medical emergencies.
• Evolving stroke: This refers to an ischemic stroke that is still underway. The blockage is in place, causing symptoms and killing brain cells. With prompt and appropriate medical attention, permanent damage may be avoided, but time is crucial.
• Completed stroke: A stroke is said to be completed when too much time has passed to be able to save the affected brain tissue. The patient will suffer permanent damage, impairment, or death.

Hemorrhagic strokes

Strokes caused by arterial ruptures, although accounting for only about 10% of all strokes, have a high fatality rate. One of the leading risk factors for hemorrhagic stroke is hypertension, or high blood pressure, which weakens the small arteries in the brain, making them susceptible to rupture. Another main cause is a condition called amyloidosis, in which amyloid is deposited along the inner walls of arteries, weakening them. In some cases, hemorrhagic strokes may be triggered by drug abuse, head trauma, brain tumors, and medications.

Hemorrhagic strokes consist of two main types:

• Intracerebral hemorrhage: In these strokes, the rupture occurs within the brain itself. About three-quarters of all hemorrhagic strokes are intracerebral hemorrhages.
• Intracranial hemorrhage: Here, the rupture occurs in the space between the skull and the brain. One type of intracranial hemorrhage, known as a subarachnoid stroke, occurs in the space between the brain and the membrane that covers it. These are often caused by a burst aneurysm, which is a balloon-like pouch that forms on a weak section of an artery. Some people are born with aneurysms, while in others, an aneurysm develops slowly over a lifetime. People with cerebral aneurysms are at particularly high risk of stroke if they smoke, have high blood pressure, or have immediate family who have experienced burst aneurysms. After a stroke caused by a burst aneurysm, doctors sometimes perform a procedure called a “clipping,” in which they clamp the base of the aneurysm to prevent a second rupture. Alternatively, they may place a metal coil into the aneurysm so that it will cause a clot to form like a dam that blocks blood from continuing to flow out and injure the brain.

No matter which type of stroke you may encounter, time is of the essence in every situation when it comes to saving your life and your abilities.