A stroke occurs when the flow of blood to a part of the brain is disrupted, causing brain cells to become damaged or die. Stroke is a leading cause of death and a major contributor to long-term disability around the world. Understanding the distinct types of stroke is important because the mechanism of injury determines the necessary emergency medical response and long-term care strategy.
Categorizing Stroke Types
Medical professionals divide strokes into two main categories based on what causes the interruption of blood flow. The most frequent type is an ischemic stroke, which makes up the vast majority of all cases. Ischemic strokes happen when a blood vessel supplying the brain becomes blocked, typically by a blood clot or a buildup of fatty deposits called plaque. This blockage deprives the downstream brain tissue of necessary oxygen and nutrients.
The second major category is a hemorrhagic stroke, which involves bleeding in or around the brain tissue. This type occurs when a blood vessel ruptures, allowing blood to leak out into the surrounding brain matter or the space between the brain and its outer membranes. The accumulated blood creates pressure on the brain, causing direct damage to the cells and disrupting normal neurological function. Although they are less frequent, hemorrhagic strokes are often associated with higher rates of death and severe disability compared to ischemic strokes.
The Prevalence of Hemorrhagic Stroke
Hemorrhagic strokes account for a smaller proportion of all stroke incidents. Globally, this type of stroke comprises approximately 10% to 15% of all reported cases. Despite their lower incidence, the effect of hemorrhagic strokes on public health is substantial.
The overall prevalence figure includes two distinct subtypes based on the location of the bleeding. The most common form is an intracerebral hemorrhage (ICH), where bleeding occurs directly into the brain tissue itself. The second type is a subarachnoid hemorrhage (SAH), which involves bleeding into the subarachnoid space, the area between the brain and the protective membranes surrounding it. Intracerebral hemorrhage is responsible for about 75% of all hemorrhagic strokes, making it the dominant subtype.
Primary Causes of Hemorrhagic Strokes
The underlying factors that lead to the rupture of blood vessels in the brain are varied but often relate to chronic vascular damage. Uncontrolled, long-term high blood pressure, known as chronic hypertension, is the single most frequent cause of intracerebral hemorrhage. Over years, the continuous high pressure on arterial walls causes structural changes, including the degeneration of the vessel lining and the formation of tiny, weak spots. These weakened small vessels can eventually rupture, leading to bleeding into the deep brain structures.
Another significant cause involves malformations or weaknesses in the arteries themselves. Aneurysms are balloon-like bulges that form on the wall of an artery due to a localized weakness. As blood flows into the bulge, the pressure can cause the thin wall to stretch and ultimately burst, frequently resulting in a subarachnoid hemorrhage.
An arteriovenous malformation (AVM) also predisposes a person to a hemorrhagic stroke. AVMs are tangled clusters of abnormal, fragile blood vessels where arteries connect directly to veins without the normal network of capillaries in between. This direct connection subjects the veins, which are not designed for high pressure, to constant arterial pressure, making them susceptible to rupture.
The use of anticoagulant medications, commonly known as blood thinners, is a growing consideration in the occurrence of hemorrhagic strokes. These drugs are prescribed to prevent blood clots in conditions like atrial fibrillation, but they also increase the overall risk of bleeding throughout the body, including the brain. The risk of hemorrhage is elevated in individuals taking these medications, particularly if the dosage is not carefully managed or if it is combined with other risk factors like uncontrolled hypertension.