A stroke is an interruption of the blood supply to any part of the brain, resulting in damaged brain tissue. It is the 3rd leading cause of death in most developed countries, and the leading cause of disability in adults. The risk doubles with each decade after age 35.
If the flow of blood in an artery supplying the brain is interrupted for longer than a few seconds, brain cells can die, causing permanent damage. An interruption can be caused by either blood clots or bleeding in the brain.
Most strokes are due to blood clots that block blood flow. Bleeding into the brain occurs if a blood vessel ruptures or there is a significant injury.
A common cause of stroke is atherosclerosis. Fatty deposits and blood platelets collect on the wall of the arteries, forming plaques. Over time, the plaques slowly begin to block the flow of blood. The plaque itself may block the artery enough to cause a stroke.
Often, the plaque causes the blood to flow abnormally, which leads to a blood clot. A clot can stay at the site of narrowing and prevent blood flow to all of the smaller arteries it supplies. (This type of clot, which doesn’t travel, is called a thrombus .) In other cases, the clot can travel and wedge into a smaller vessel. (A clot that travels is called an embolism .)
Strokes caused by embolism are most commonly caused by heart disorders. An embolism may originate in a major blood vessel as it branches off the heart. A clot can also form elsewhere in the body for any number of reasons, and then travel to the brain, causing a stroke.
Arrhythmias of the heart, such as atrial fibrillation, can be associated with this type of stroke and may contribute to clot formation. Other causes of embolic stroke include endocarditis (an infection of the heart valves), or use of a mechanical heart valve. A clot can form on the artificial valve, break off, and travel to the brain. For this reason, those with mechanical heart valves must take blood thinners.
BLEEDING IN THE BRAIN
A second major cause of stroke is bleeding in the brain ( hemorrhagic stroke ). This can occur when small blood vessels in the brain become weak and burst. Some people have defects in the blood vessels of the brain that make this more likely. The flow of blood after the blood vessel ruptures damages brain cells.
High blood pressure is the number one reason that you might have a stroke. The risk of stroke is also increased by age, family history of stroke, smoking, diabetes, high cholesterol, and heart disease.
Certain medications promote clot formation and may increase your chances for a stroke. One example is birth control pills, especially if a woman taking them also smokes and is older than 35.
Women have a risk of stroke during pregnancy and the weeks immediately after pregnancy. Overall, however, more men have strokes than women.
Cocaine use, alcohol abuse, head injury, and bleeding disorders increase the risk of bleeding into the brain.