Strokes

DEFINITION: Stroke, or a cerebrovascular accident (CVA), is the severe reduction or cessation of blood flow to the brain, resulting in a variety of serious and often permanent impairments depending on the area of the brain affected. A transient ischemic attack (TIA) is a temporary, brief loss of blood to the brain, accompanied by temporary impairment of vision, numbness, or other symptoms; it may herald a stroke.

ALSO KNOWN AS: Cerebrovascular accidents (CVAs)

ANATOMY OR SYSTEM AFFECTED: Blood vessels, brain, circulatory system, head, heart, nervous system, psychic-emotional system

CAUSES: Hypertension, diabetes, cerebral aneurysm, high cholesterol levels, smoking, atherosclerosis, personal or family history of strokes or TIAs

SYMPTOMS: Vision impairment, numbness, aphasia, slurred speech, relaxed facial muscles, general muscle weakness, dizziness, unsteadiness, sudden falls, headaches, confusion, stupor

DURATION: Acute

TREATMENTS: Surgical revascularization (endarterectomy), balloon angioplasty, drugs, physical therapy

Causes and Symptoms

Strokes produce damage to portions of the brain as a result of decreased blood supply. Strokes are commonly known as cerebrovascular accidents (CVAs). Symptoms of strokes will vary depending on the part of the brain that is affected. Resulting speech disorders may include aphasia (loss of the ability to speak) or dysarthria (difficulty in speaking). A sudden weakness or numbness of one side of the body is known as hemiparesis or hemiplegia. The eyes can also be involved. A dimness or transient loss of vision, particularly in one eye, is called amaurosis fugax. Occasionally, it can involve the same portion of the visual field in both eyes. Other symptoms of stroke may include dizziness, unsteadiness, sudden falls, headaches, confusion, or stupor. Coma is less commonly involved in a stroke.

Predisposing factors to strokes include hypertension (high blood pressure), diabetes, high cholesterol, smoking, atherosclerotic disease in other portions of the body (such as the heart or legs), and a previous or family history of strokes or transient ischemic attacks.

In cerebrovascular disease, atherosclerosis affects the arteries that circulate blood to the brain. The brain receives blood from two major sets of arteries. The carotid arteries, in the front of the neck, supply the anterior (front) portions of the brain. The vertebral arteries travel through the transverse processes of the spine and join the basilar artery to provide blood to the posterior (back) portion of the brain. Both circulatory systems are joined within the brain in a structure known as the circle of Willis, a composite of arteries that join to form an anatomical circle. The various arteries supply the necessary blood flow to different areas of the brain. Only 25 to 50 percent of people have a complete circle of Willis; this anatomical variance may be a factor in the severity of the stroke.

In atherosclerotic disease, fat, cholesterol, and calcium deposits are laid down along the walls of the arteries, primarily at sites where arteries divide and natural turbulence tends to occur. These components build up to form plaques, which may cause stenosis (narrowing) and occlusion (closure) of the arterial lumen. Accumulation of platelets and other blood cells can form a thrombus (blood clot) along with plaque buildup, which also may obstruct the arteries. Pieces of plaque or thrombotic material may break off and cause emboli to lodge acutely in the main vessels or their more distant branches.

Transient ischemic attacks (TIAs), also referred to as ministrokes, may herald a stroke. TIAs produce similar symptoms to stroke but cause no permanent damage. By definition, TIAs last less than twenty-four hours; usually, they last only a few minutes. Most TIAs are produced by emboli. An embolus occurs when a piece of plaque from the lining of a major artery breaks off and temporarily blocks the blood flow to a particular area of the brain. If the symptoms last for more than twenty-four hours, a cerebrovascular accident, cerebral infarct, or stroke has occurred. A reversible ischemic neurological deficit (RIND) is similar to a stroke in that it is an event that lasts for more than twenty-four hours but resolves in about seventy-two hours.

The majority of strokes (85 percent) are the result of impaired blood flow (ischemia) to the brain; strokes may also be caused by a leaking or ruptured blood vessel in the brain (hemorrhagic stroke). Atherosclerosis in the cerebrovascular system will cause similar symptoms of ischemia in other portions of the body. There is increasing narrowing, or stenosis, of blood vessels. Eventually, they will close off completely and become occluded. The development of new, small vessels that bypass a diseased artery is called collateralization. This process requires weeks or months to occur. Collateralization seems to be especially prominent in the cerebrovascular system, since the brain is an organ that requires constant blood flow at all times. Eventual occlusion or thrombosis of a major vessel causes the majority of CVAs, producing significant ischemia in a portion of the brain.

In certain cases, the blockage is acute, having resulted from an embolus or thrombus that blocks an artery. If collateralization has not developed, the damage to an affected structure is more severe. A thrombus or embolus can also arise from the heart. This is most common in individuals who have had a recent heart attack, who have disease that involves the mitral valve, or who have atrial fibrillation, a variety of irregular heartbeat. Another cause of stroke is cerebral hemorrhage, or bleeding into the brain, which is also occasionally referred to as apoplexy. Hypertension is the most common cause of intracranial bleeding and accounts for 10 to 15 percent of cases. Other causes of strokes are cerebral aneurysms (5 to 7 percent), tumors that have developed blood supplies (3 to 5 percent), and genetic bleeding tendencies (1 to 2 percent).

A cerebral aneurysm occurs when the wall of an artery becomes weak and enlarges like a balloon. These aneurysms often rupture. With a ruptured cerebral aneurysm and subsequent hemorrhage, by-products of red blood cell degeneration may produce a condition called vasospasm, wherein the arteries will constrict. This often leads to ischemia. One or more thrombi are often formed in an aneurysm. If they break loose, they can become emboli, float until they become lodged in a small blood vessel, block the flow of blood, and cause ischemia. This can ultimately lead to a stroke.

Stroke refers to the disease process that is mainly produced by atherosclerotic changes in the arteries to the brain. Contributing or significant risk factors in the development of atherosclerosis include hypertension (high blood pressure), hyperlipidemia (high levels of cholesterol in the blood), smoking, diabetes mellitus, and a family history of similar incidents. Evidence of atherosclerotic disease in other portions of the body, such as the heart or legs, increases the risk of stroke. Atherosclerosis is a generalized disease process that affects arterial beds throughout the body.

Symptoms of TIAs in structures near the front of the brain, the area supplied by the carotid arteries, include hemiparesis, a numbness or loss of function in half of the body. Hemiplegia, a weakness of an arm or leg (or both), can be attributable to disease in the carotid artery on the side of the body opposite to the affected body part. Another relatively common problem usually caused by disease in the left carotid artery is aphasia, a speech disorder. Disease in either carotid artery can cause amaurosis fugax, or blindness in one eye. Victims often describe this condition as a shade being drawn over the eye.

Other, more generalized symptoms are the result of problems in the vertebral arteries or the blood vessels at the base of the brain, which supply the back portions of the brain. Associated symptoms include dizziness, a loss of orientation often produced by decreased blood flow to the brain. Dizziness is frequently caused by abrupt positional changes, in which blood pressure will suddenly fall with rapid standing or sitting, or by cardiac arrhythmias (irregular heartbeats), which prevent adequate amounts of blood flow from being delivered during certain cardiac cycles.

Vertigo is different from dizziness. Individuals suffering from vertigo experience a spinning sensation that may be accompanied by nausea. A common cause for vertigo is a condition known as subclavian steal, in which atherosclerotic disease affects the arteries of the arms just prior to the point where the vertebral arteries branch off. As an arm is used, or with abrupt changes in head position, blood will flow out of the vertebral arteries in a reverse manner (the so-called steal) to aid circulation in the arm (via the subclavian arteries) and vertigo will ensue. In addition, imbalance and other visual disturbances may be associated with problems in the vertebral arteries. These symptoms may also result from cerebrovascular disease in which inadequate blood supply to multiple areas of the brain can produce diverse symptoms.

In the majority of strokes, symptoms last twenty-four to seventy-two hours. Approximately 25 percent of patients will develop permanent deficits that will affect them for the rest of their lives. Approximately 20 percent of individuals who have strokes will experience no symptoms (be asymptomatic) and not know that they have had a stroke. They are unlikely to even develop TIAs. Such unheralded events result from occlusion or thrombosis of the blood vessels in the brain. This causes ischemia that leads to infarction or cell death in a particular section of the brain.

Asymptomatic cerebrovascular disease, however, can often be detected by the presence of a bruit, a French word meaning “noise.” Stenosis in arteries can be compared to rapids in a river. Blood will flow very quickly through the narrow area and create turbulence, producing a bruit that can be heard with a stethoscope. Patients with narrowing in the carotid arteries ranging from 20 to 80 percent may possess a bruit. The absence of a bruit does not mean that the carotid arteries are disease-free. Once the stenosis reaches critical proportions, the flow is diminished and turbulence may be negligible, indicating a severe stenosis or an occluded artery. Often, doctors will recommend elective surgery to patients with coronary artery stenosis between 60 and 80 percent in an effort to reestablish blood flow and prevent eventual occlusion and possible stroke. About 75 percent of strokes are caused by ischemia that results from the above process. Crescendo TIAs, in which multiple TIAs occur in a brief period of time, and evolving strokes require immediate medical treatment. Appropriate diagnosis and treatment may prevent a stroke or decrease its severity.

Although disease caused by an aneurysm is a separate entity, it may be associated with atherosclerotic disease in certain cases. Most aneurysms within the brain produce no symptoms. As aneurysms increase in size, the probability of rupture increases; therefore, elective surgery may be recommended. Occasionally, diagnoses of cerebral aneurysms are made during investigations of other cerebral events, such as headaches. Acute onset of severe headaches or stiff neck should mandate immediate medical attention, since rupture of a cerebral aneurysm often manifests itself in this manner.

Treatment and Therapy

Strokes and TIAs often occur quickly and without warning. The best treatment for them is preventive behavior to avoid the atherosclerotic disease leading to such events. Preventative measures include dietary changes to lower blood pressure such as lowering one's intake of sodium and saturated fats and increasing intake of potassium, fruits, and vegetables. Other important preventative measures include increased physical activity, weight loss (if overweight or obese), smoking cessation, and maintaining a healthy blood pressure. For those at high risk for a cardiovascular event such as stroke or heart attack, statin therapy or a low dose of aspirin every other day may be beneficial. When a stroke or TIA is suspected, however, a complete history and physical examination is usually the first component of diagnosis. Eliciting symptoms and noting significant risk factors and findings upon physical examination will help a physician determine the primary area of the brain affected, schedule the appropriate tests for further diagnosis, and choose the best course of therapy.

Because of the high incidence of death and disability associated with strokes, a variety of diagnostic tests have been developed since the 1950s. One of the oldest noninvasive methods is the directional Doppler test. A Doppler device employs a probe with one or two piezoelectric crystals. An ultrasonic signal using a frequency of 2 to 5 megahertz (MHz) is sent into the body. Movement of red blood cells causes a shift in the frequency of the signal that is transmitted back. The amount of shift is proportional to the speed of blood flow. This device can also be used to determine the direction of blood flow. By listening with a continuous-wave Doppler over a branch of the ophthalmic artery at the corner of the eye and performing certain compression maneuvers on the arteries that supply the face, information regarding possible collateral pathways can be obtained concerning internal carotid artery blockages of greater than 75 percent.

The vascular surgeon William Gee developed another device, called an ocular pneumoplethysmograph (OPG). The OPG utilizes cups placed in the eye to measure the ocular pressure. A vacuum is applied to the eyes, effectively blocking the ophthalmic arteries, which are the first major branches of the internal carotid artery. As the vacuum is released, the blood flow is reestablished and the appearance of arterial pulsations is noted on a strip chart. These pulsations denote systolic blood pressure in the ophthalmic arteries. A pressure difference of 5 millimeters of mercury (mm Hg) between the two eyes or an index of less than 0.66 (comparing the systolic blood pressure in the ophthalmic artery with that in the brachial artery) is consistent with carotid artery blockage of more than 50 to 75 percent.

Both of these methods are indirect tests, in which significant internal carotid artery disease is implied if the test is positive. Deficiencies in the test procedures include quantification of the percentage of carotid artery disease or differentiation of significant stenosis from occlusions. They also may be wrong if the vertebral or basal arteries contribute significant collateral blood flow. The OPG is still used in certain situations as a quick screening tool, but the directional Doppler has lost favor as an accurate diagnostic test.

Duplex ultrasound machines, first employed in the early 1980s, utilize B-mode (brightness-mode) ultrasound to visualize the vessels and type of plaque. In comparison, Doppler ultrasound can audibly evaluate the blood flow in the vessels. Using real-time spectrum analyzers, the Doppler signals are then analyzed in terms of velocity (speed of the blood flow) and waveform characteristics. The greater the velocity, the greater the amount of stenosis. Absence of blood flow will denote occlusions. Today, computed tomography (CT) and angiography are most likely to be used to assess a patient's risk of heart attack or stroke.

Computed tomography (CT) scanning is a radiological technique that provides a three-dimensional picture of the brain and its structures. Occasionally, a contrast medium is also used in this examination. CT scanning is especially useful in the diagnosis of cerebral aneurysms and areas of infarct. Magnetic resonance imaging (MRI) is a nonradiological technique that also provides exceptional three-dimensional images of the soft tissue structures of the brain. MRI can detect cerebral infarcts at an earlier stage than can CT scanning.

Arteriography or angiography is performed in a hospital setting. A catheter is placed in one of the arteries, and dye containing iodine is injected. Multiple X-rays are then taken to visualize the circulation. Arteriograms are considered to be standard in diagnosis. The delineation of the blockages and collateral pathways is then used primarily to plan surgical procedures.

Low-dose aspirin is often prescribed to alleviate symptoms of TIAs and to help protect patients from strokes or heart attacks. Although it is a powerful drug in decreasing the incidence of embolus formation, a national study has demonstrated that patients with a history of TIAs and carotid artery stenosis of greater than 60 percent should undergo surgical revascularization to protect against major strokes. The chances of having a stroke after experiencing a TIA are approximately 40 percent greater.

Endarterectomy is a surgical technique in which the inner wall and part of the middle wall of the carotid artery are excised, effectively scraping out atherosclerotic plaques. Although used in other arterial segments, endarterectomy is the most common surgical procedure used to revascularize the carotid arteries.

Other techniques for intervention have been developed. Percutaneous balloon angioplasty involves placing a balloon catheter in the diseased segment during an angiogram. When the balloon catheter is inflated, it opens up the area of stenosis or small segment of occlusion. This method has been employed in the coronary arteries as well as in the vessels leaving the aorta, the iliac arteries, and arteries in the lower extremities. It is not used often in the treatment of atherosclerotic plaques in the cerebral circulation because of the possibility of emboli traveling to the more distant blood vessels of the brain or eye. Some success in the use of balloon angioplasty has been reported in the treatment of vasospasm.

New drugs that dissolve clots may be used alone or in combination with balloon angioplasty or surgery. Although effective in the treatment of coronary artery and peripheral vascular disease, their use in the cerebral circulation has been restricted because of the risk of embolus formation or bleeding complications.

Perspective and Prospects

Stroke was the fifth leading cause of death in the United States, according to the Centers for Disease Control and Prevention (CDC), with approximately 165,393 deaths occurring in 2022. Worldwide, stroke is the second leading cause of death, according to the World Health Organization, causing more than 6.2 million deaths in 2019. Cardiovascular disease is the leading cause of death worldwide, causing 17.9 million deaths per year.

Control of blood pressure and hyperlipidemia, the development of new drugs and diagnostic techniques, reduced tobacco use, and the advent of cardiovascular surgery in the early 1950s have all contributed to a reduced disease burden and annual death rate. Unfortunately, strokes are still prevalent given the extent of atherosclerotic disease in the American population, which is largely attributed to a high-fat and high-sodium diet and rising rates of obesity. Worldwide, rates of cerebrovascular disease are increasing, particularly in low- and middle-income countries. Furthermore, stroke mortality differs widely based on race, gender, and geographic location. Atherosclerosis is more prevalent in men and older adults. Women have more protection until the onset of the menopause. Within five years of the menopause, however, the stroke and death rates of men and women tend to equalize. Ethnic African and Asian populations also appear to be at a greater risk. Public awareness initiatives on stroke prevention, particularly on the importance of a healthy diet and regular exercise, will continue to lower rates of stroke mortality.

Since the 1950s, a number of both noninvasive and invasive procedures have been developed to diagnose atherosclerotic disease. Cardiovascular surgical techniques were developed in the 1950s. The first coronary artery bypass surgery performed in the United States occurred in 1960. The development of ultrasound devices in the 1950s initiated the research into using these noninvasive devices to diagnose cerebrovascular disease. The duplex devices introduced commercially in the late 1970s and early 1980s have spurred the development of new diagnostic devices for detecting atherosclerotic disease. These devices allow for visualization of plaque morphology (composition of the plaque, such as thrombus, calcium, hemorrhage, and other particulate matters) and blood flow characteristics for a better understanding of the disease process. Computed tomography and angioplasty have further contributed to improved assessments of cardiovascular risks. These noninvasive technologies also allow physicians to monitor the effects of new drugs and techniques in the treatment of atherosclerosis. Advances in digital subtraction and computer enhancement of angiographic techniques, along with new contrast media, have made arteriograms safer and more accurate.

Aspirin still remains a potent drug in the treatment of TIAs in patients with lesser degrees of disease and in postsurgery patients. Recognition and prompt treatment of symptomatic cerebrovascular symptoms remain the key to better survival rates.

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