Radiology Profile of Stroke

Saturday, November 19, 2016

Stroke

The American Heart Association AHA reports that cerebrovascular disorder such as ischemic and hemorrhagic strokes constitute the 3rd most frequent cause of death in North America. This stroke is the leading cause of long term disability. Approximately 20 to 30 percent of stroke victims don’t survive and almost 55% of stroke patient survivors have a disability. Despite the significant advances in the treatment of stroke in recent years, cerebrovascular disorders continue to pose a considerable challenge to acute neurovascular management.

Treatment Options of Stroke

Therapeutic options, such as thrombolytic therapy, can limit the extend of brain injury and improve outcome after stroke when administered to patients who fall within narrow clinical guidelines. But these treatment therapies are only effective if given early after the stroke has begun, hence the criticality of emergent imaging. However, these therapies are expensive and may result in potentially life threatening complications, drawbacks that make it crucial that each case be assessed by its individual risk benefit ratio.

Types of Stroke

Stroke may be divided into two main categories.
Ischemic Stroke Ischemic Stroke is caused by a blockage in an artery. Ischemic strokes are by far the most common, accounting for 80% of all strokes. Ischemia is defined as a deficiency of oxygen in vital tissues.
There are 2 main types of Ischemic stroke exist:

  • Thrombotic Stroke it is caused form a blood clot or a fatty deposit within one of the brain’s artery.
  • Embolic Stroke is resulting from a traveling particle that forms elsewhere and is too large to pass through small vessels and eventually lodges in a smaller artery.
In addition to these two types of stroke, a less acute form of ischemic stroke exists, and this form is referred to as a lacunar stroke.

Thrombotic Stroke

Thrombotic stroke occure when a clot that forms as the result of atherosclerosis block an artery that supplies blood to the brain. This condition is progressive and can be summarized like as follows.

Arterial walls slowly thicken, harden and narrow, this is creating stenosis until blood flow is reduced.
The abnormal arteries become vulnerable to injury, initiating an inflammatory response. It is hypothesized that this response plays a significant role in the evolution of stroke.

  • The immune system reacts to the arteria injuries by releasing white blood cells at the site, specifically neutrophils and macrophages.
  • Macrophages digest foreign debris, turning them into foamy cells that attach to the smooth muscle cells of the blood vessels, causing a buildup of the of these cells.
  • Sensing fusther harm, the immune system releases factors called cytokines, which attract more white blood cells and perpetuate the entire cycle.
  • These processes impede blood flow
  • To make matters worse, the injured inner walls of vessels fail to produce enough nitric oxide, a substance critical for maintaining blood vessel elasticity. Without adequate nitric oxide, arteries become calsified and lose elasticity.
  • Hardened and rigid arteries are even more susceptible to injury. If they tear, a thrombus or clot may form.
  • If that happens, a clot could completely block the already narrowed artery, preventing oxygen from reaching a part of the brain, and stroke occurs.

Embolic Stroke

Embolic stroke is caused when an artery in the brain is suddenly blocked by embolic material, which is usually a thrombus that developed elsewhere in the body. The embolus travels within the cervicocranial arteries until it becomes wedged in an artery in the brain. If the embolic material lodges for very long time, the blood flow reduces in that particular artery, or known as hypoperfusion, this will result in an infact. This infarct may become hemorrhagic when the embolus moves, or fragments and reperfusion occurs.


Lacunar Stroke

Lacunar stroke occurs in a small arteries such as those that supply the deep cerebral white matter, are also susceptible to atherosclerotic changes. A lacunar stroke occurs when one of these arteries is blocked. In these deep parts of the brain, no other blood vessels exist that can help supply blood to that region. Therefore, a blockage results in tissue death in that area. The word lacuna describe a small, hallow cavity or pit. After a lacunar stroke, the tiny infarct that result have been described as hallowed out thus the name lacunar.
Lacunar infarct are a series of very tiny ischemic strokes. Symptoms present in the patient as clumsiness, weakness, and emotional variability. Lacunar stroke accounts for 25% of stroke and can sometimes serve as a warning sign that a major stroke may be imminent.

Hemorrhagic Stroke

Hemorrhagic Stroke are rupture of a blood vessel in the brain causes leakage of blood into the brain parenchyma, Cerebrospinal fluid CSF spaces around the brain or both. Approximately 20% of stroke occur from hemorrhagic strokes are classified by how and where they occur.

Intracerebral Hemorrhage Stroke

Intracerebral hemorrhagic stroke occur within the brain parenchyma itself, and a hematoma often results. These strokes account for more than of hemorrhagic strokes. Most often, this type of stroke result from hypertension, which exerts excessive pressure on arterial walls already damaged by atherosclerosis. Heart attack patients who have been given drugs either to break up blood clots or to thin blood to reduce the likelihood of developing clots have a slightly elevated risk of this type of stroke.

Subarachnoid Hemorrhage

Subarachnoid hemorrhage strokes occur when there is bleeding into the subarachnoid spaces and the Cerebrospinal fluid spaces. These strokes are usually caused by the rupture of an aneuryem.

Arteriovenous Malformation

Arteriovenous malformation AVMs are composed of tangles of arteries and arterialized veins. There is brain tissue interposed between the vessels, but it is usually abnormal and often scarred from previous tiny hemorrhages. The patient may not have been aware of these tiny hemorrhage of may have experienced them as bad headaches.

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