Stroke

Overview

Strokes, or brain attacks, are a major cause of death and permanent disability. They occur when blood flow to a region of the brain is obstructed and may result in death of brain tissue.

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.

Warning Signs of Stroke

Strokes, or brain attacks, are medical emergencies that require immediate medical attention. Warning signs of stroke include the following:

• Sudden numbness or weakness, especially on one side of the body
• Sudden confusion
• Sudden vision problems in one or both eyes
• Sudden difficulty walking, dizziness, loss of balance or coordination
• Sudden, severe headache with no known cause
• Sudden difficulty speaking or understanding speech

Incidence and Prevalence

Stroke is the third leading cause of death and the leading cause of disability in the United States. Approximately 600,000 strokes, or brain attacks, occur in the United States each year and of these, approximately 150,000 (25%) are fatal. The incidence of stroke is higher in African Americans than Caucasians.

Stroke occurs at an equal rate in men and women, but women are more likely to die. Ischemic stroke occurs more frequently in people over age 65 and hemorrhagic stroke is more common in younger people.

Warning Signs

The American Stroke Association has identified several warning signs of a stroke, or brain attack. 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

Types of Stroke

Ischemic Stroke

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.

Lacunar infarct (approx. 20% of cases) usually occurs as a result of arterial blockage caused by high blood pressure (hypertension). This type of stroke has the best prognosis.

A transient ischemic attack (TIA) is a transient event that is a risk factor for ischemic stroke. In a TIA, arterial blockage in the brain occurs briefly and resolves on its own, without causing tissue death. Approximately 10% of ischemic strokes are preceded by a TIA, and about 40% of patients who experience a TIA will have a stroke.

Hemorrhagic Stroke

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.

Epidural hematoma (i.e., a collection of blood) develops in the potential space between the outer membrane (dura) and the skull.

Subdural hematoma develops in the potential space between the dura and the middle layer membrane (arachnoid). This condition may become chronic when shrinkage (atrophy) of the brain (often seen in elderly patients) allows the brain to move more freely within the skull. High velocity impact to the skull may cause acute subdural hematoma, which is often fatal.

Subarachnoid hemorrhage develops in the cerebrospinal fluid-filled space between the arachnoid and the inner membrane (pia), which contains major blood vessels. Subarachnoid hemorrhages are usually caused by a ruptured aneurysm or head injury.

Intracerebral hemorrhage occurs in blood vessels located in the cerebrum, brain stem, cerebellum, or spinal cord.

Risk Factors

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:

• Alcohol abuse
• Brain tumor
• Cardiac conditions (e.g., myocardial infarction [heart attack], mitral regurgitation)
• Coagulopathy (blood clotting disorder)
• Diabetes
• 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
• Smoking
• Sudden rise in blood pressure
• Surgical incision of an artery (treatment for atherosclerosis)

Risk factors for hemorrhagic stroke include untreated aneurysm, congenital (present at birth) arteriovenous malformations (AVMs), and traumatic brain injury (TBI).

Causes

Stroke occurs when blood flow to a region of the brain is obstructed, causing brain tissue death. Ischemic stroke is usually caused by a blood clot in an artery that supplies blood to the brain. Introduction of a foreign substance into the bloodstream may also cause ischemic stroke. For example, an air embolism may occur in deep-sea divers who surface too quickly or may be introduced during intravenous injection.

Hemorrhagic stroke is caused by ruptured blood vessel (aneurysm), arteriovenous malformation (AVM, blood vessel defect), tumor, or traumatic brain injury.

Signs and Symptoms

A stroke, or brain attack, is a medical emergency that requires immediate medical attention. Because most strokes do not cause severe pain, patients often delay seeking treatment, resulting in extensive brain tissue damage.

Symptoms of stroke depend on the type and which area of the brain is effected. Signs of ischemic stroke usually occur suddenly, and signs of hemorrhagic stroke usually develop gradually. Symptoms include the following:

• Difficulty speaking or understanding speech (aphasia)
• Difficulty walking
• Dizziness or lightheadedness (vertigo)
• Numbness, paralysis, or weakness, usually on one side of the body
• Seizure (relatively rare)
• Severe headache with no known cause
• Sudden confusion
• Sudden decrease in the level of consciousness
• Sudden loss of balance or coordination
• Sudden vision problems (e.g., blurry vision, blindness in one eye)
• Vomiting

In transient ischemic attacks (TIAs), one or more symptoms occur suddenly, last a few minutes, and then subside. These "ministrokes" also require immediate medical attention to reduce the risk for damage to brain tissue and to evaluate the risk for stroke.

Complications stroke Stroke is the leading cause of disability in the United States. Prompt medical treatment reduces the risk for irreversible complications and permanent disability. Complications may result from ischemic cascade or develop as a result of the patient becoming immobile or bedridden.

Complications that may occur within 72 hours of stroke include the following:

• Cerebral swelling (edema)
• Increased intracranial pressure (ICP)
• Intracerebral hemorrhage
• Seizures

Paralysis on one side of the body (hemiparesis) and speech problems may occur as a result of ischemic cascade. Complications that may develop gradually as a result of immobility include the following:

• Bedsores
• Blood clots
• Fibrosis of connective tissue resulting in decreased mobility
• Malnutrition
• Pneumonia
• Urinary tract infections (UTIs; if a catheter is required)

More than 30% of stroke patients require assistance with daily living and approximately 15% require care in an assisted-living facility (e.g., nursing home, rehabilitation center). Approximately 20% of stroke patients require help walking (e.g., cane, walker) and as many as 33% suffer from depression. Treatment for stroke usually involves rehabilitation.

Diagnosis

If stroke is suspected, prompt, accurate diagnosis and treatment is necessary to minimize brain tissue damage. Diagnosis includes a medical history and a physical examination including neurological examination to evaluate the level of consciousness, sensation, and function (visual, motor, language) and determine the cause, location, and extent of the stroke.

Physical examination includes assessing the airway, breathing, and circulation (ABCs) and the vital signs (i.e., pulse, respiration, temperature). The head (including ears, eyes, nose, and throat) and extremities are also examined to help determine the cause of the stroke and rule out other conditions that produce similar symptoms (e.g., Bell's palsy).

Blood tests (e.g., complete blood count) and imaging procedures (e.g., CT scan, ultrasound, MRI) help the physician determine the type of stroke and rule out other conditions, such as infection and brain tumor.

Imaging Procedures When stroke is suspected, computed tomography (CT scan) is performed as soon as possible. CT scan produces x-ray images of the brain and is used to determine the location and extent of hemorrhagic stroke. CT scan usually cannot produce images showing signs of ischemic stroke until 48 hours after onset, so a repeat scan may be performed.

Ultrasound uses high-frequency sound waves to produce images of blood flow through the arteries in the neck that supply blood to the brain (i.e., carotid arteries) and may be used to detect blockage.

Magnetic resonance imaging (MRI scan) with magnetic resonance angiography (MRA) uses a magnetic field to produce detailed images of brain tissue and arteries in the neck and brain, allowing physicians to detect small-vessel infarct (i.e., stroke in small blood vessels deep in brain tissue).

Angiogram involves injecting a contrast agent (dye) into the bloodstream and taking a series of x-rays of blood vessels. This test is used to identify the source and location of arterial blockage and to detect aneurysms and blood vessel defects.

An electrocardiogram may be performed to detect reduced blood flow to the heart (myocardiac ischemia) or irregular heartbeat (cardiac arrhythmia).

Single photon emission computed tomography (SPECT) and positron emission tomography (PET) involve injecting a radioactive substance into the bloodstream and monitoring it as it travels through blood vessels in the brain. These tests allow physicians to detect damaged regions of the brain resulting from reduced blood flow.

Treatment

Early treatment can help minimize damage to brain tissue and improve the outcome (prognosis). Treatment depends on whether the stroke is ischemic or hemorrhagic and on the underlying cause of the condition. The long-term goals of treatment include rehabilitation and prevention of additional strokes.

Ischemic Stroke

Initial treatment for ischemic stroke involves removing the blockage and restoring blood flow. Tissue plasminogen activator (t-PA) is a medication that can break up blood clots and restore blood flow when administered within 3 hours of the event. This medication carries a risk for increased intracranial hemorrhage and is not used for hemorrhagic stroke. Mannitol, a diuretic, may be administered intravenously (through an IV) to reduce intracranial pressure during an ischemic stroke.

Antihypertensives such as labetalol (Normodyne®) and enalapril (Vasotec®) may be used alone or in combination with diuretics to treat high blood pressure. Side effects are usually mild and include dizziness, fatigue, and headache.

Antiplatelet agents such as aspirin, clopidogrel bisulfate, and aspirin with dipyridamole (Aggrenox®) may be prescribed to reduce the risk for recurrent stroke. Aspirin may also improve the outcome of a stroke when administered within 48 hours. Side effects include stomach pain, heartburn, nausea, and gastrointestinal bleeding. Aggrenox is taken orally, twice a day, and may also cause headache.

Clopidogrel bisulfate (Plavix®) is an antiplatelet medication that is taken orally, once a day, to help prevent the formation of blood clots. It is prescribed for patients with atherosclerosis who have had a recent stroke and is used to prevent recurrence. Patients with medical conditions that may cause internal bleeding (e.g., stomach ulcers) should not use clopidogrel.

Side effects include abdominal pain, rash, diarrhea, and headache. Serious side effects (e.g., gastrointestinal hemorrhage) are rare. Physicians and dentists should be informed that a patient is taking clopidogrel before any surgery is scheduled.

Anticonvulsants such as diazepam (Valium®) and lorazepam (Ativan®) may be prescribed for patients who experience recurrent seizures after a stroke. Side effects include drowsiness, fatigue, and weakness.

Anticoagulants such as warfarin (Coumadin®) may be prescribed to prevent the formation of blood clots. Patients taking warfarin may require regular blood tests to monitor coagulation (blood clot formation) and prevent abnormal bleeding.

Hemorrhagic Stroke

Hemorrhagic stroke usually requires surgery to relieve intracranial (within the skull) pressure caused by bleeding. Most of the damage caused by this type of stroke results from the physical disruption of brain tissue.

Surgical treatment for hemorrhagic stroke caused by an aneurysm or defective blood vessel can prevent additional strokes. Surgery may be performed to seal off the defective blood vessel and redirect blood flow to other vessels that supply blood to the same region of the brain.

Endovascular treatment involves inserting a long, thin, flexible tube (catheter) into a major artery, usually in the thigh, guiding it to the aneurysm or the defective blood vessel, and inserting tiny platinum coils (called stents) into the blood vessel through the catheter. Stents support the blood vessel to prevent further damage and additional strokes.

Rehabilitation

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).

Prognosis

Prognosis depends on the type of stroke, the degree and duration of obstruction or hemorrhage, and the extent of brain tissue death. Most stroke patients experience some permanent disability that may interfere with walking, speech, vision, understanding, reasoning, or memory.

Approximately 70% of ischemic stroke patients are able to regain their independence and 10% recover almost completely. Approximately 25% of patients die as a result of the stroke. The location of a hemorrhagic stroke is an important factor in the outcome, and this type generally has a worse prognosis than ischemic stroke.

Prevention

The following measures may help prevent stroke:

• Do not smoke.
• Exercise regularly.
• 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.

People with hypertension or diabetes can reduce their risk for stroke by controlling their condition through proper medication and appropriate lifestyle modifications (e.g., regular exercise, weight loss).

Carotid endarterectomy is a surgical procedure in which atherosclerotic deposits (plaque) in a carotid artery are removed. This procedure can reduce the risk for stroke.