The causes of strokes depend upon the type of stroke you have. So, let’s take a look at some of the various stroke types and what causes them, both the direct and indirect or underlying causes. For example, the actual cause of a stroke may be a blood clot, but the clot may have formed due to uncontrolled or too high cholesterol. So, let’s look at two specific stroke types:
1. Ischemic stroke
Most strokes fall under this category, in fact, about 80 percent of strokes are ischemic strokes. Ischemic strokes are caused by not enough blood in the brain. They occur when blood clots or other particles block arteries to your brain and cause severely reduced blood flow, which is called ischemia.
When this happens your brain cells are deprived of oxygen and nutrients, and cells often begin to die within minutes.
Within the category of ischemic strokes are some sub categories of strokes that have varying places and reasons there is not enough blood in the brain:
a. Thrombotic stroke. This type of stroke will happen when a blood clot (which is also called a thrombus, hence the reason for the name) forms in one of the arteries that supply blood to your brain(The carotid arteries). So, if these are caused by clots, what causes the clots? A clot forms in areas damaged by atherosclerosis, which is a disease where the arteries are clogged accumulated plaque. Plaque is a cholesterol-containing fatty deposit.
b. Embolic stroke. An embolic stroke will happen when a blood clot or other particle forms in a blood vessel away from your brain and is swept through your bloodstream and lodges in a narrower brain artery. Most often this clot forms in the heart. This type of blood clot is called an embolus, and is usually caused by atrial fibrillation, which is irregular beating in the heart’s two upper chambers.
2. Hemorrhagic stroke
The term for this stroke type comes from the word hemorrhage. Hemorrhage is the medical word for bleeding. What causes this stroke type is when a blood vessel in your brain leaks or ruptures. So, the underlying causes of this stroke are uncontrolled high blood pressure (hypertension), weak spots in your blood vessel walls (aneurysms), and a combination of the two. Another, but less common cause of hemorrhage is the rupture of an arteriovenous malformation (AVM), which is a malformed tangle of thin-walled blood vessels, present at birth.
There are two types of hemorrhagic stroke:
a. Intracerebral hemorrhage. This is when a blood vessel in the brain bursts and spills into the surrounding brain tissue, damaging cells, and depriving the brain cells beyond the leak of blood. The most common cause of this type of hemorrhagic stroke is high blood pressure. High blood pressure can cause small arteries inside your brain to become brittle and susceptible to cracking and rupture.
b. Subarachnoid hemorrhage. For this particular type of stroke, bleeding starts in a large artery on or near the membrane surrounding the brain and spills into the space between the surface of your brain and your skull. With this type of stroke you will get a sudden and severe headache. So, what causes this type of stroke? Subarachnoid strokes are commonly caused by the rupture of an aneurysm, which can develop with age or result from a genetic predisposition.Further stroke damage is caused after the initial rupture because vessels may go into vasospasm, which is a condition in which arteries near the hemorrhage constrict erratically, causing brain cell damage by further restricting or blocking blood flow to portions of the brain.