The illustration shows how an ischemic stroke can occur in the brain. If a blood clot breaks away from plaque buildup in a carotid (neck) artery, it can travel to and lodge in an artery in the brain. The clot can block blood flow to part of the brain, causing brain tissue death..
A stroke occurs if the flow of oxygen-rich blood to a portion of the brain is blocked. Without oxygen, brain cells start to die after a few minutes. Sudden bleeding in the brain also can cause a stroke if it damages brain cells. If brain cells die or are damaged because of a stroke, symptoms occur in the parts of the body that these brain cells control. Examples of stroke symptoms include sudden weakness; paralysis or numbness of the face, arms, or legs (paralysis is an inability to move); trouble speaking or understanding speech; and trouble seeing. An ischemic stroke occurs if an artery that supplies oxygen-rich blood to the brain becomes blocked. Blood clots often cause the blockages that lead to ischemic strokes. The two types of ischemic stroke are thrombotic and embolic. In a thrombotic stroke, a blood clot (thrombus) forms in an artery that supplies blood to the brain. In an embolic stroke, a blood clot or other substance (such as plaque, a fatty material) travels through the bloodstream to an artery in the brain. (A blood clot or piece of plaque that travels through the bloodstream is called an embolus. With both types of ischemic stroke, the blood clot or plaque blocks the flow of oxygen-rich blood to a portion of the brain. A hemorrhagic stroke occurs if an artery in the brain leaks blood or ruptures (breaks open). The pressure from the leaked blood damages brain cells. The two types of hemorrhagic stroke are intracerebral and subarachnoid. In an intracerebral hemorrhage, a blood vessel inside the brain leaks blood or ruptures. In a subarachnoid hemorrhage, a blood vessel on the surface of the brain leaks blood or ruptures. When this happens, bleeding occurs between the inner and middle layers of the membranes that cover the brain. In both types of hemorrhagic stroke, the leaked blood causes swelling of the brain and increased pressure in the skull. The swelling and pressure damage cells and tissues in the brain. The illustration shows how a hemorrhagic stroke can occur in the brain. An aneurysm in a cerebral artery breaks open, which causes bleeding in the brain. The pressure of the blood causes brain tissue death. An ischemic stroke or transient ischemic attack (TIA) occurs if an artery that supplies oxygen-rich blood to the brain becomes blocked. Many medical conditions can increase the risk of ischemic stroke or TIA. For example, Atherosclerosis is a disease in which a fatty substance called plaque builds up on the inner walls of the arteries. Plaque hardens and narrows the arteries, which limits the flow of blood to tissues and organs (such as the heart and brain). Plaque in an artery can crack or rupture. Blood platelets, which are disc-shaped cell fragments, stick to the site of the plaque injury and clump together to form blood clots. These clots can partly or fully block an artery. Plaque can build up in any artery in the body, including arteries in the heart, brain, and neck. The two main arteries on each side of the neck are called the carotid arteries. These arteries supply oxygen-rich blood to the brain, face, scalp, and neck. When plaque builds up in the carotid arteries, the condition is called carotid artery disease. Carotid artery disease causes many of the ischemic strokes and TIAs that occur in the United States. An embolic stroke (a type of ischemic stroke) or TIA also can occur if a blood clot or piece of plaque breaks away from the wall of an artery. The clot or plaque can travel through the bloodstream and get stuck in one of the brain’s arteries. This stops blood flow through the artery and damages brain cells. Heart conditions and blood disorders also can cause blood clots that can lead to a stroke or TIA. For example, atrial fibrillation, or AF, is a common cause of embolic stroke. In AF, the upper chambers of the heart contract in a very fast and irregular way. As a result, some blood pools in the heart. The pooling increases the risk of blood clots forming in the heart chambers. An ischemic stroke or TIA also can occur because of lesions caused by atherosclerosis. These lesions may form in the small arteries of the brain, and they can block blood flow to the brain. Sudden bleeding in the brain can cause a hemorrhagic stroke. The bleeding causes swelling of the brain and increased pressure in the skull. The swelling and pressure damage brain cells and tissues. Examples of conditions that can cause a hemorrhagic stroke include high blood pressure, aneurysms, and arteriovenous malformations (AVMs). “Blood pressure” is the force of blood pushing against the walls of the arteries as the heart pumps blood. If blood pressure rises and stays high over time, it can damage the body in many ways. Aneurysms are balloon-like bulges in an artery that can stretch and burst. AVMs are tangles of faulty arteries and veins that can rupture within the brain. High blood pressure can increase the risk of hemorrhagic stroke in people who have aneurysms or AVMs. The major risk factors for stroke include: High Blood pressure. High blood pressure is the main risk factor for stroke. Blood pressure is considered high if it stays at or above 140/90 mmHg over time. If you have diabetes or chronic kidney diseases, high blood pressure is defined as 130/80 mmHg or higher. (The mmHg is millimeters of mercury—the units used to measure blood pressure.) Smoking. Smoking can damage blood vessels and raise blood pressure. Smoking also may reduce the amount of oxygen that reaches your body’s tissues. Exposure to secondhand smoke also can damage the blood vessels. Diabetes. Diabetes is a disease in which the blood sugar level is high because the body doesn’t make enough insulin or doesn’t use its insulin properly. Insulin is a hormone that helps move blood sugar into cells where it’s used for energy. Heart diseases. Coronary heart disease (also called coronary artery disease),cardiomyopathy, heart failure, and atrial fibrillation can cause blood clots that can lead to a stroke. Brain aneurysms or arteriovenous malformations (AVMs). Aneurysms are balloon-like bulges in an artery that can stretch and burst. AVMs are tangles of faulty arteries and veins that can rupture (break open) within the brain. AVMs may be present at birth, but often aren’t diagnosed until they rupture. Personal or family history of stroke or TIA. If you’ve had a stroke, you’re at higher risk for another one. Your risk of having a repeat stroke is the highest right after a stroke. A TIA also increases your risk of having a stroke, as does having a family history of stroke. Following a healthy lifestyle can lower the risk of stroke. Some people also may need to take medicines to lower their risk.
Stroke
What Is a Stroke?
Ischemic Stroke
Illustration – Ischemic Stroke
Hemorrhagic Stroke
What Causes a Stroke?