There are two main types of stroke: ischemic and hemorrhagic. Ischemic stroke is caused by blockage in an artery that supplies blood to the brain, resulting in a deficiency in blood flow (ischemia). Hemorrhagic stroke is caused by the bleeding of ruptured blood vessels (hemorrhage) in the brain.
During ischemic stroke, diminished blood flow initiates a series of events (called ischemic cascade) that may result in additional, delayed damage to brain cells. Early medical intervention can halt this process and reduce the risk for irreversible complications.
Approximately 80% of strokes, or brain attacks, are ischemic. They can develop in major blood vessels on the surface of the brain (called large-vessel infarcts) or in small blood vessels deep in the brain (called small-vessel infarcts). Types of ischemic stroke include embolic infarct, thrombotic infarct, and lacunar infarct. Infarct of undetermined cause accounts for approximately 30% of cases of ischemic stroke.
Tissue death caused by lack of blood (embolic infarct) occurs suddenly when a blood clot (embolism) forms in one part of the body, travels through the bloodstream, and lodges in and obstructs a blood vessel in the brain. Cardiac embolism, in which a blood clot forms in the heart, accounts for about 20-30% of ischemic strokes.
Thrombotic infarct (approx. 10-15% of cases) occurs when a blood clot forms in an artery that supplies the brain, causing tissue death. This type usually occurs as a result of plaque build-up in arteries (atherosclerosis ) and develops over time.
Hemorrhagic stroke occurs when a blood vessel in the brain ruptures and bleeds into surrounding tissue. The bleeding compresses nearby blood vessels and deprives surrounding tissue of oxygen, causing stroke. Hemorrhagic stroke usually affects a large area of the brain, is severe, and carries a high risk for death.
Intracranial hemorrhages occur when blood vessels located between the brain and the skull rupture. They can result from traumatic brain injury (TBI) or develop spontaneously as the result of a blood vessel defect or weakness such as a bulge in an artery (aneurysm) or arteriovenous malformation (AVM).
Blood vessel defects can be present at birth (congenital; e.g., berry aneurysm, arteriovenous malformation) or acquired (e.g., atherosclerotic aneurysm). Atherosclerotic aneurysm develops when plaque build-up weakens the arterial wall.
Intracranial hemorrhage occurs in the space between the brain and the skull, or cranium. Three membranes-the dura, arachnoid, and pia-surround the brain and spinal cord.
Risk Factors for Stroke
The primary risk factor for ischemic stroke is age (over age 65). High blood pressure (hypertension) and heart disease are also major risk factors. Maintaining healthy blood pressure through diet, exercise, and medication, if necessary, can decrease the risk for stroke.
Atrial fibrillation occurs when muscles in the atria contract too quickly, resulting in an irregular heartbeat (arrhythmia). Arrhythmia alters blood flow and may cause blood clots to form in the heart. These clots can travel through blood vessels to the brain, causing stroke. Atrial fibrillation causes an almost five-fold increase in the risk for stroke.
Other risk factors include the following:
Cardiac conditions (e.g., myocardial infarction [heart attack], mitral regurgitation)
Coagulopathy (blood clotting disorder)
Drug abuse (may cause decreased blood flow)
Fibromuscular dysplasia (causes stenosis and hypertension)
Family or personal history of stroke
High blood pressure (hypertension)
High cholesterol (hypercholesterolemia)
Infection (e.g., meningitis, endocarditis)
Narrowing of arteries (arterial stenosis)
Plaque build-up in arteries (atherosclerosis)
Secondary hemorrhage following an ischemic stroke
Sickle cell disease
Sudden rise in blood pressure
Surgical incision of an artery (treatment for atherosclerosis)
Warning Signs of Stroke
Strokes, or brain attacks, are medical emergencies that require immediate medical attention. The American Stroke Association has identified several stroke warning signs. Remember that someone having a stroke may not experience all of the warning signs and that warning signs can come and go. Anyone having these symptoms should seek prompt medical attention. The sooner treatment begins, the more effective it is.
Warning signs of a stroke include the following:
Sudden numbness or weakness of the face, arm, or leg, especially on one side of the body
Sudden confusion, difficulty speaking or understanding
Sudden difficulty seeing in one or both eyes
Sudden difficulty walking, dizziness, loss of balance or coordination
Sudden severe headache with no known cause
Recovery and rehabilitation are import aspects of stroke treatment. In some cases, undamaged areas of the brain may be able to perform functions that were lost when the stroke occurred.
Rehabilitation includes physical therapy, speech therapy, and occupational therapy. Physical therapy involves using exercise and other physical means (e.g., massage, heat) to help patients regain the use of their arms and legs and prevent muscle stiffness in patients with permanent paralysis.
Speech therapy helps patients regain the ability to speak. Occupational therapy helps patients regain independent function and relearn basic skills (e.g., buttoning a shirt, preparing a meal, bathing).
Prevention of Stroke
The following measures may help prevent stroke:
Do not smoke.
Limit dietary intake of salt, alcohol, and saturated fat.
Maintain body weight within an ideal range.
Use airbags, seatbelts, and child safety seats in automobiles.
Wear protective helmets when engaging in contact sports, horseback riding, or riding bicycles.