Stroke

Stroke

A stroke, known medically as a cerebrovascular accident (CVA), is the rapidly developing loss of brain function(s) due to disturbance in the blood supply to the brain. This can be due to ischemia (lack of blood flow) caused by blockage (thrombosis, arterial embolism), or a hemorrhage (leakage of blood). As a result, the affected area of the brain is unable to function, leading to inability to move one or more limbs on one side of the body, inability to understand or formulate speech, or an inability to see one side of the visual field.

Definition:

The traditional definition of stroke, devised by the World Health Organization in the 1970s, is a "neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours". This definition was supposed to reflect the reversibility of tissue damage and was devised for the purpose, with the time frame of 24 hours being chosen arbitrarily. The 24-hour limit divides stroke from transient ischemic attack, which is a related syndrome of stroke symptoms that resolve completely within 24 hours. With the availability of treatments that, when given early, can reduce stroke severity, many now prefer alternative concepts, such as brain attack and acute ischemic cerebrovascular syndrome (modeled after heart attack and acute coronary syndrome respectively), that reflect the urgency of stroke symptoms and the need to act swiftly.

What is a stroke?

Brain cell function requires a constant delivery of oxygen and glucose from the bloodstream. A stroke, or cerebrovascular accident (CVA), occurs when blood supply to part of the brain is disrupted, causing brain cells to die. Blood flow can be compromised by a variety of mechanisms.

Blockage of an artery

* Narrowing of the small arteries within the brain can cause a lacunar stroke, (lacune means "empty space"). Blockage of a single arteriole can affect a tiny area of brain causing that tissue to die (infarct).

* Hardening of the arteries (atherosclerosis) leading to the brain. There are four major blood vessels that supply the brain with blood. The anterior circulation of the brain that controls most motor activity, sensation, thought, speech, and emotion is supplied by the carotid arteries. The posterior circulation, which supplies the brainstem and the cerebellum, controlling the automatic parts of brain function and coordination, is supplied by the vertebrobasilar arteries.

If these arteries become narrow as a result of atherosclerosis, plaque or cholesterol, debris can break off and float downstream, clogging the blood supply to a part of the brain. As opposed to lacunar strokes, larger parts of the brain can lose blood supply, and this may produce more symptoms than a lacunar stroke.

* Embolism to the brain from the heart. In some instances blood clots can form within the heart and the potential exists for them to break off and travel (embolize) to the arteries in the brain and cause a stroke.

Rupture of an artery (hemorrhage)

* Cerebral hemorrhage (bleeding within the brain substance). The most common reason to have bleeding within the brain is uncontrolled high blood pressure. Other situations include aneurysms that leak or rupture or arteriovenous malformations (AVM) in which there is an abnormal collection of blood vessels that are fragile and can bleed.

Causes of stroke

Blockage of an artery

The blockage of an artery in the brain by a clot (thrombosis) is the most common cause of a stroke. The part of the brain that is supplied by the clotted blood vessel is then deprived of blood and oxygen. As a result of the deprived blood and oxygen, the cells of that part of the brain die and the part of the body that it controls stops working. Typically, a cholesterol plaque in a small blood vessel within the brain that has gradually caused blood vessel narrowing ruptures and starts the process of forming a small blood clot.

Risk factors for narrowed blood vessels in the brain are the same as those that cause narrowing blood vessels in the heart and heart attack (myocardial infarction). These risk factors include:

* high blood pressure (hypertension),

* high cholesterol,

* diabetes, and

* smoking.

Embolic stroke

Another type of stroke may occur when a blood clot or a piece of atherosclerotic plaque (cholesterol and calcium deposits on the wall of the inside of the heart or artery) breaks loose, travels through the bloodstream and lodges in an artery in the brain. When blood flow stops, brain cells do not receive the oxygen and glucose they require to function and a stroke occurs. This type of stroke is referred to as an embolic stroke. For example, a blood clot might originally form in the heart chamber as a result of an irregular heart rhythm, such as occurs in atrial fibrillation. Usually, these clots remain attached to the inner lining of the heart, but occasionally they can break off, travel through the blood stream, form a plug (embolism) in a brain artery, and cause a stroke. An embolism can also originate in a large artery (for example, the carotid artery, a major artery in the neck that supplies blood to the brain) and then travel downstream to clog a small artery within the brain.

Cerebral hemorrhage

A cerebral hemorrhage occurs when a blood vessel in the brain ruptures and bleeds into the surrounding brain tissue. A cerebral hemorrhage (bleeding in the brain) causes stroke symptoms by depriving blood and oxygen to parts of the brain in a variety of ways. Blood flow is lost to some cells. As well, blood is very irritating and can cause swelling of brain tissue (cerebral edema). Edema and the accumulation of blood from a cerebral hemorrhage increases pressure within the skull and causes further damage by squeezing the brain against the bony skull further decreasing blood flow to brain tissue and cells.

Subarachnoid hemorrhage

In a subarachnoid hemorrhage, blood accumulates in the space beneath the arachnoid membrane that lines the brain. The blood originates from an abnormal blood vessel that leaks or ruptures. Often this is from an aneurysm (an abnormal ballooning out of the wall of the vessel). Subarachnoid hemorrhages usually cause a sudden, severe headache, nausea, vomiting, light intolerance, and a stiff neck. If not recognized and treated, major neurological consequences, such as coma, and brain death may occur.

Vasculitis

Another rare cause of stroke is vasculitis, a condition in which the blood vessels become inflamed causing decreased blood flow to brain tissue.

Migraine headache

There appears to be a very slight increased occurrence of stroke in people with migraine headache. The mechanism for migraine or vascular headaches includes narrowing of the brain blood vessels. Some migraine headache episodes can even mimic stroke with loss of function of one side of the body or vision or speech problems. Usually, the symptoms resolve as the headache resolves.

Risk factors for stroke

Overall, the most common risk factors for stroke are:

* high blood pressure,

* high cholesterol,

* smoking,

* diabetes and

* increasing age.

Heart rhythm disturbances like atrial fibrillation, patent foramen ovale, and heart valve disease can also be the cause.

When strokes occur in younger individuals (less than 50 years old), less common risk factors to be considered include illicit drugs, such as cocaine or amphetamines, ruptured aneurysms, and inherited (genetic) predispositions to abnormal blood clotting.

An example of a genetic predisposition to stroke occurs in a rare condition called homocystinuria, in which there are excessive levels of the chemical homocystine in the body. Scientists are trying to determine whether the non-hereditary occurrence of high levels of homocystine at any age can predispose to stroke.

Stroke diagnosis:

A stroke is a medical emergency. Anyone suspected of having a stroke should be taken to a medical facility immediately for evaluation and treatment. Initially, the doctor takes a medical history from the patient if possible or from others familiar with the patient if they are available. Important questions include what the symptoms were, when they began, if they were getting better, worse or staying the same. Past medical history adds important information looking for risk factors for stroke and for medications that can cause bleeding (for example, warfarin [Coumadin], clopidogrel [Plavix], prasugrel [Effient]).

Physical examination is key in confirming the parts of the body that have stopped functioning and may help determine what part of the brain has lost its blood supply. If available, a neurologist, a doctor specializing in disorders of the nervous system and diseases of the brain, can assist in the diagnosis and management of stroke patients.

Just because a person has slurred speech or weakness on one side of the body does not necessarily signal the occurrence of a stroke. There are many other possibilities that can be responsible for these symptoms. Other conditions that can mimic a stroke include:

* brain tumors,

* brain abscess (a collection of pus in the brain caused by bacteria or a fungus),

* migraine headache,

*bleeding in the brain either spontaneously or from trauma,

* meningitis or encephalitis,

* an overdose of certain medications, or

* an electrolyte imbalance in the body. Abnormal concentrations (too high or too low) of sodium, calcium, or glucose in the body may also cause changes in the nervous system that can mimic a stroke.

In the acute stroke evaluation, many things will occur at the same time. As the physician is taking the history and performing the physical examination, nursing staff will begin monitoring the patient's vital signs, performing blood tests, and performing an electrocardiogram (EKG or ECG).

Part of the physical examination that is becoming standardized is the use of a stroke scale. The American Heart Association has published a guide to the examination of the nervous system to help health care practitioners determine the severity of a stroke and whether aggressive intervention may be warranted.

There is a narrow time frame to intervene in an acute stroke with medications to reverse the loss of blood supply to part of the brain (please see TPA below). The patient needs to be appropriately evaluated and stabilized before any clot-busting drugs can be potentially utilized.

Computerized tomography: In order to help determine the cause of a suspected stroke, a special X-ray test called a CT scan of the brain is often performed. A CT scan is used to look for bleeding or masses within the brain that may cause symptoms that mimic a stroke, but are not treated with thrombolytic therapy with TPA.

MRI scan: Magnetic resonance imaging (MRI) uses magnetic waves rather than X-rays to image the brain. The MRI images are much more detailed than those from CT, but due to the length of time to do the test and lack of availability of the machines in many hospitals, is not a first line test in stroke. While a CT scan may be completed within a few minutes, an MRI may take more than an hour to complete. An MRI may be performed later in the course of patient care if finer details are required for further medical decision making. People with certain medical devices (for example, pacemakers) or other metals within their body, cannot be subjected to the powerful magnetic field of an MRI.

Other methods of MRI technology: An MRI scan can also be used to specifically view the blood vessels non-invasively (without using tubes or injections), a procedure called an MRA (magnetic resonance angiogram). Another MRI method called diffusion weighted imaging (DWI) is being offered in some medical centers. This technique can detect the area of abnormality minutes after the blood flow to a part of the brain has ceased, whereas a conventional MRI may not detect a stroke until up to six hours after it has started, and a CT scan sometimes cannot detect it until it is 12 to 24 hours old. Again, this is not a first line test in the evaluation of a stroke patient, when time is of the essence.

Computerized tomography with angiography: Using dye that is injected into a vein in the arm, images of the blood vessels in the brain can give information regarding aneurysms or arteriovenous malformations. Moreover, other abnormalities of brain blood flow may be evaluated. With faster machines and better technology, CT angiography may be done at the same time as the initial CT scan to look for a blood clot within an artery in the brain.

CT and MRI images often require a radiologist to interpret their results.

Conventional angiogram: An angiogram is another test that is sometimes used to view the blood vessels. A long catheter tube is inserted into an artery in the groin or arm and threaded into the arteries of the brain. Dye is injected while X-rays are taken and information can be obtained about blood flow in the brain. The decision to perform CT angiography versus conventional angiography depends upon a patient's specific situation and the technical capabilities of the hospital.

Carotid Doppler ultrasound: A carotid Doppler ultrasound is a non-invasive test that uses sound waves to look for narrowing or stenosis and decreased blood flow in the carotid arteries (the major arteries in the front of the neck that supply blood to the brain).

Heart tests: Certain tests to evaluate heart function are often performed in stroke patients to search for the source of an embolism. Electrocardiograms (EKG or ECG) may be used to detect abnormal heart rhythms like atrial fibrillation that are associated with embolic stroke.

Ambulatory rhythm monitoring may be considered if the patient complains of palpitations or passing out episodes (syncope) and the doctor cannot find reason for it on the EKG. The patient can wear a Holter monitor for 1-2 days and sometimes longer looking fro a potential electrical conduction problem with the heart.

Echocardiograms or ultrasounds of the heart can help evaluate the structure and function of the heart including the heart muscle, valves and the motion of the heart chamber when the heart beats. As well, specifically for stroke patients, this test may be able to find blood clots within the heart and the presence of a patent foramen ovale, both potential causes of stroke.

Blood tests: In the acute situation, when the patient is in the midst of a stroke, blood tests are done to check for anemia, kidney and liver function, electrolyte abnormalities and blood clotting function.

In other situations, when time is not of the essence, similar blood tests may be done. In addition, screening test for inflammation may be considered including an ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein). These are non specific tests that may give direction to medical care.