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Guide To Stroke in Women
What is blood?
How does blood clot?
|What Causes A Stroke?
There are two main types of stroke: ischemic stroke and hemorrhagic stroke. Both types of stroke have different causes. Ischemic strokes are caused by a blockage in an artery supplying blood to the brain and hemorrhagic strokes are caused by a burst blood vessel in the brain which causes blood to leak into the surrounding tissue. Why an artery should become blocked or rupture can vary. We will discuss some of the most common causes in this article.
Atherosclerosis (image) is a process where arteries (blood vessels) in the body become gradually narrowed due to the buildup of fatty deposits in the lining of their walls. If a blood clot (thrombosis) forms somewhere in the body it can become lodged in a narrowed artery, suddenly cutting off blood supply. When it occurs in the arteries of the heart (one of the main causes of coronary heart disease) it can lead to heart attacks. If it occurs in the arteries supplying blood to the brain it can lead to stroke. Usually atherosclerosis in the coronary (heart) arteries causes warning signs such as chest pain and angina attacks. This means the person has time to undergo heart disease testing and possibly take medication to prevent a heart attack. Atherosclerosis in the arteries supplying the brain is less likely to produce warning signs; the first sign may be a mini stroke which indicates the problem is already severely progressed. Vascular screening, using ultrasound technology on the neck arteries to detect narrowing or blockages, may be recommended to people at with high stroke risk factors.
Traveling Blood Clots
Sometimes a thrombosis will develop in the arteries supplying the brain - but in other instances it may form in another part of the body, such as the coronary arteries, and travel towards the brain. This can happen when a piece of atherosclerotic plaque breaks off, for example in a coronary artery, and travels through the bloodstream until it encounters a narrowed artery in the brain. There it forms a plug (embolism) and causes what is called an embolic stroke. Problems with the heart such as atrial fibrillation (irregular heartbeats), heart failure or hole in the heart can cause an embolism to form. An embolism can also start in the carotid artery of the neck and travel downstream until it reaches a small narrowed vessel in the brain.
There is some evidence that people with migraine headaches are 3 to 6 times more likely to suffer a stroke caused by a clot than healthy people. Scientists do not understand why this is the case, but one theory is that migraines cause the brain blood vessels to spasm, first narrowing and then swelling. This makes it easier for a clot to lodge and cause a blockage. Occasionally a spasm (without a clot) can narrow an artery long enough to cut off blood supply to the brain causing stroke symptoms. Symptoms however usually disappear again. Doctors now recommend patients with migraines to control their stroke risk factors - in particular, not to smoke, and where applicable to manage high blood pressure and diabetes.
Ruptured Blood Vessels
An aneurysm (image) is an outward bulge or ballooning in a blood vessel caused by pressure of blood pressing against a weakened artery wall. Not all aneurysms burst, some remain small and harmless. But if the bulge is stretched too far, perhaps aggravated by high blood pressure, atherosclerosis or the effects of smoking, the aneurysm can burst. An aneurysm can form in any artery of the body, when it forms in the brain it is known as a cerebral aneurysm. Signs of a cerebral aneurysm include headaches and blurred vision if it presses on surrounding nerves or tissues. If it bursts, it causes a hemorrhagic stroke. This causes blood to flow into surrounding tissue increasing pressure on the skull (edema) as the brain is squeezed against the skull. Additionally, if blood leaks from the vessels, it means the part of the brain it was suppose to supply with blood to is now on limited supply. This causes brain cells and brain function to permanently die. In most instances aneurysms are genetically inherited.
A stroke can also be caused by a congenital (birth) abnormality in the brain called an arteriovenous malformation (although this is relatively rare). The cause of this malformation is not clear but it results in a tangled mass of arteries and veins that can be found in the brain or spinal cord. Pressure can build up in these vessels, leading to a rupture and hemorrhage stroke. Often arteriovenous malformation does not cause symptoms for years and then leads to recurring headaches and seizures as blood starts to leak into the brain or spinal cord. If you have these symptoms your doctor will order an MRI scan or angiography to check the vessels. It can be treated by surgery. However if a vessel ruptures before diagnosis and treatment the person can die suddenly.