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Types of Stroke
There are two main types of stroke — ischemic and hemorrhagic. Ischemic stroke occurs when there is blockage of an artery supplying the brain tissue while hemorrhagic stroke occurs when a weakened vessel ruptures causing leakage of blood into or around the brain itself. Transient ischemic attacks (TIAs) occur when there is a transient blockage of blood flow to the brain, resulting in transient stroke like symptoms.
Treatment for each type of stroke is significantly different. In fact, treating an ischemic stroke as though it were hemorrhagic or vice versa could have life-threatening consequences. Therefore, a reliable diagnosis is critical before beginning treatment.
About 80% of strokes are ischemic. They are caused by an obstruction of an artery supplying the brain, which prevents oxygenated blood from reaching parts of the brain that the artery feeds. Ischemic strokes are either thrombotic or embolic, depending on where the clot originated from.
Thrombotic Ischemic Stroke
Thrombotic stroke is caused by a thrombus (blood clot) that develops in an artery supplying blood to the brain. This usually occurs because of repeated buildup of fatty deposits, calcium and clotting factors such as fibrinogen, and cholesterol, in the blood. The body perceives the buildup as an injury to the vessel wall and responds the way it would to a small wound — it forms blood clots around the injured area. This progressive build-up of clot eventually blocks blood flow.
Large vessel thrombosis occurs in the brain’s larger arteries. The impact and damage tends to be magnified because all the smaller vessels that the artery feeds are deprived of blood. In most cases, large vessel thrombosis is caused by a combination of long-term plaque buildup (atherosclerosis) followed by rapid blood clot formation. High cholesterol is a common risk factor for this type of stroke.
Small vessel disease (lacunar infarction) occurs when blood flow is blocked to a very small artery. It has been linked to high blood pressure (hypertension) and is an indicator of atherosclerotic disease.
Thrombotic disease accounts for about 60 percent of acute ischemic strokes. Of these, approximately 70 percent are large vessel thrombosis.
Embolic Ischemic Stroke
An embolus is a blood clot that forms in one area of the body and travels through the bloodstream to another. In the case of embolic stroke, a clot usually forms in the heart or large arteries of the upper chest and neck. It then travels to the smaller vessels of the brain where it lodges and blocks blood flow.
Emboli can be fat globules, air bubbles or, most commonly, pieces of atherosclerotic plaque that have detached from an artery wall. Many emboli are caused by a cardiac condition called atrial fibrillation, which is an abnormal, rapid heartbeat in which the two small upper chambers of the heart (called the atria) quiver instead of beat. This quivering causes blood to pool and form clots that can travel to the brain and cause a stroke. Cardiac sources of embolism account for 80 percent of embolic ischemic strokes.
Ischemic Stroke Symptoms
The most common symptom of an ischemic stroke is sudden weakness of the face, arm or leg, most often on one side of the body. Other warning signs may include:
- Sudden numbness of the face, arm, or leg, especially on one side of the body;
- Sudden confusion, trouble speaking or understanding speech;
- Sudden trouble seeing in one or both eyes;
- Sudden trouble walking, dizziness, loss of balance or coordination;
- Sudden severe headache with no known cause (most common with hemorrhagic stroke).
The symptoms depend on the side of the brain that's affected, the part of the brain, and how severely the brain is injured. Stroke may be associated with a headache, or may be completely painless. Therefore, each person may have different warning signs.
Transient Ischemic Attack (TIA)
A Transient ischemic attack (TIA) or “mini-stroke” is caused by a brief disruption in blood flow to a part of the brain. The symptoms of a TIA resemble those of a stroke but they usually resolve within minutes or up to 24 hours and there is no damage to the brain. Patients can experience any of the following symptoms: loss of vision, dizziness, imbalance, weakness or loss of sensation on one side of the body, confusion, difficulty speaking or understanding, and generalized weakness A TIA is usually a warning sign of an impending stroke and should be considered an emergency. It is vital to present to the nearest primary stroke center for urgent evaluation and treatment in order to prevent a stroke from occurring.
Hemorrhagic stroke occurs when a vessel in the brain suddenly ruptures causing blood to leak directly into brain tissue and/or into the clear cerebrospinal fluid that surrounds the brain as well as in its central cavities (ventricles). The rupture can be caused by the force of high blood pressure. It can also originate from a weak spot in a blood vessel wall, such as a cerebral aneurysm, or other blood vessel malformations in or around the brain.
Damage can be caused in two ways. As in the case of ischemic stroke, oxygen- and nutrient-rich blood is prevented from reaching the brain cells beyond the point of rupture. In addition, extravasated blood can irritate and harm the brain cells in the areas where it accumulates.
It is the location of the hemorrhage, rather than the amount of blood, that tends to be the bigger factor in influencing the severity of the stroke. For example, tiny bleeds in the brainstem can be quite lethal whereas the same-sized bleed in the frontal lobe may not even result in symptoms.
There are different types of hemorrhagic strokes. They are differentiated by where the ruptured artery is located and where the bleed occurs.
Intracerebral Hemorrhage (ICH)
Also called intraparenchymal hemorrhage or intracranial hematoma, this type of stroke is caused by the sudden rupture of an artery or blood vessel within the brain. The blood that leaks into the brain results in a sudden increase in pressure that can damage the surrounding brain cells. If the amount of blood increases rapidly, the sudden and extreme buildup in pressure can lead to unconsciousness or death.
Approximately 10 percent of all strokes are intracerebral hemorrhages. They occur most commonly in the basal ganglia where the vessels can be particularly delicate. High blood pressure (hypertension) is the most common cause of this type of stroke. Less common causes include trauma, infections, tumors, blood clotting deficiencies, and abnormalities in cerebral blood vessels.
Blood Vessel Abnormalities
Blood vessel abnormalities in the brain include arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs). AVMs and AVFs are abnormal connections between cerebral arteries (which carry blood to the brain) and veins (which take blood away from the brain).
AVMs appear to be acquired prior to birth (congenital) and tend to form near the back of the brain. Although AVFs can be congenital, they are more often caused by trauma that damages an artery and a vein that are adjacent in the brain.
These blood vessel abnormalities can cause a host of problems but most commonly they exert pressure against the adjacent parts of the brain and cause neurological problems such as seizures, paralysis or loss of speech. They can also bleed (hemorrhage) into surrounding tissues. 2 to 4 percent of all strokes are due to hemorrhage from a cerebral arteriovenous abnormality.
Subarachnoid Hemorrhage (SAH)
Subarachnoid hemorrhage occurs when bleeding from a damaged vessel causes blood to accumulate in the subarachnoid space between the brain and the skull. This blood presses on the surface of the brain and can irritate, damage or destroy surrounding brain cells.
When blood enters the subarachnoid space, it mixes with the cerebrospinal fluid (CSF) that cushions the brain and spinal cord. This blood can block CSF circulation and lead to fluid buildup, increasing pressure on the brain. The open spaces in the brain (ventricles) may enlarge and result in a condition called hydrocephalus. This can make a patient lethargic, confused or incontinent.
The blood also can also irritate and lead to narrowing of the blood vessels. This condition, referred to as vasospasm, can impede blood flow to the brain and result in an ischemic stroke. Vasospasm typically develops five to eight days after the initial hemorrhage.
After trauma, the most common cause of a subarachnoid hemorrhage is a ruptured cerebral aneurysm. SAH also can occur when blood leaks from abnormal blood vessel connections (AVMs and AVFs) near the surface of the brain.
A cerebral aneurysm is a weak and bulging area in the wall of an artery very that is akin to a thin balloon or weak spot in an inner tube. Aneurysms form when there is wear and tear in the arteries, injury, infection, or an inherited tendency to form them.
There are two types of aneurysm:
Saccular Aneurysm – This is the most common type. It has a neck and stem and is known as a “berry” aneurysm because of its shape.
Fusiform Aneurysm – These are dilatations in the walls of a vessel and are commonly located at the base of the brain in the Circle of Willis. This is an area where significant blood pressure changes occur and where a lot of vessels branch off. These factors weaken the walls of blood vessels in this area.
Although it is not possible to predict whether an aneurysm will rupture, an aneurysm is more likely to do so when it has a diameter of 7 millimeters or more. Unruptured brain aneurysms can be medically treated to prevent a possible rupture.
Sudden & Severe Symptoms
Symptoms of a hemorrhagic stroke appear without warning. The sudden increase in blood volume within the rigid skull (cranium) creates intense intracranial pressure that cannot be released. This, in turn, may trigger a severe (“thunderclap”) headache, neck pain, double vision, nausea or vomiting, loss of consciousness or even death.
About 17 percent of strokes are hemorrhagic. The average age at which people suffer hemorrhagic stroke tends to be lower than for ischemic stroke. This is because many of the risk factors are related to unhealthy behaviors, such as smoking or drug use, rather than the effects of aging on the body.The fatality rate for hemorrhagic strokes is higher than for ischemic strokes and overall prognosis is poorer