A stroke occurs when brain cells die due to the interruption of blood flow to part of the brain. With over half a million people in the US experiencing strokes each year, they are the leading cause of disability and the third leading cause of death. Strokes are more prevalent among men and African-Americans, and two thirds of them occur in people over the age of 65.
Brain cells die quickly when the blood supply is interrupted because the blood no longer delivers oxygen or removes the cell’s waste products. The sooner treatment is received after a stroke, the better the chances of survival. Depending on the part of the brain affected, a stroke may cause:
- Loss of memory
- Speech problems
- Loss of reasoning ability
Strokes are mostly classified by what causes them. The two main types are ischemic, which make up about 85-90 percent of stroke incidents, and hemorrhagic. Ischemic strokes are subdivided into embolic, thrombotic, watershed strokes and venous thrombosis. Watershed strokes are also known as border zone stroke or systemic hypoperfusion. Hemorrhagic strokes are subdivided into those that occur inside the brain and subarachnoid hemorrhages, which occur on the brain’s surface.
Symptoms in an embolic stroke tend to appear much more suddenly than those of a thrombosis. They include:
- Decreased vision or blurring
- Severe headache
- Paralysis, weakness or numbness in the arm, leg or face, usually in only one side of the body
- Dizziness or loss of balance or coordination
Embolic strokes occur when an embolus, or a traveling particle in a blood vessel, flows into increasingly smaller arteries until it gets lodged and restrains the passage of blood. An embolus can be a blood clot, plaque that has broken off from a blood vessel, fat, air, or even cancerous cells. An embolism may also develop when certain heart arrhythmias or other heart conditions allow blood to pool and coagulate.
In a thrombotic stroke, rather than traveling through blood vessels, a clot builds up and impedes passage of blood through the artery where it forms. A tear in an artery wall attracts platelets and natural clotting agents that accumulate and form a clot. These in turn send chemicals that may trigger a clotting cascade.
While most arterial clots form around atherosclerotic plaques, plaque can also build up on the wall of an artery, causing it to stiffen and narrow, restricting blood in a condition known as arterial stenosis. Most obstructions in thrombotic events take longer to form, which is what generally causes the onset of thrombotic strokes to take longer than that of embolic strokes.
Watershed strokes are caused by hypotension (low blood pressure) or other vascular problems such as vasculitis (a kind of inflammation of the blood vessels). These events can cause hypofusion, or diminished blood flow which can damage brain tissue between arteries.
In venous thrombosis, the blood vessel in which the blood clot forms and causes an infarction is a vein, which returns blood to the heart. A rare form of the disease known as sinus vein thrombosis can cause strokes.
Hemorrhagic strokes occur in about ten percent of strokes. In this type of stroke, a blood vessel bursts in the brain and spills blood into spaces around brain cells. Hemorrhagic strokes usually carry a greater risk of permanent disability and death than ischemic strokes.
Drugs associated with strokes include Vioxx and the Ortho Evra birth control patch. Most Vioxx strokes result from a blood clot directly in the brain or neck. Ortho Evra releases estrogen on an ongoing basis. Estrogen can act as a coagulant which promotes or contributes to the formation of a blood clot. Both drugs can cause deep vein thrombosis (DVT), usually in the legs, pelvis or arms. The clot can then dislodge and travel to the lung, where it causes a pulmonary embolism (PE), eventually leading to stroke.
A stroke requires immediate intervention. The patient is typically stabilized and given a plasminogen activator (tPA) or another blood-thinning agent such as heparin or even ordinary aspirin. If caught in time, the blood clot will begin to dissolve immediately and normal blood flow to the brain is restored.
Of those who survive a stroke, about ten percent recover completely, another ten percent require institutional care, and the remaining can return home to their daily routines with the help of therapy and rehabilitation.