Difference between revisions of "Cerebrovascular disease"

Latest revision as of 20:28, 21 September 2010

Cerebrovascular disease is a group of brain dysfunctions related to disease of the blood vessels supplying the brain. Hypertension is the most important cause; it damages the blood vessel lining, endothelium, exposing the underlying collagen where platelets aggregate to initiate a repairing process which is not always complete and perfect. Sustained hypertension permanently changes the architecture of the blood vessels making them narrow, stiff, deformed, uneven and more vulnerable to fluctuations in blood pressure.

A fall in blood pressure during sleep can then lead to a marked reduction in blood flow in the narrowed blood vessels causing ischemic stroke in the morning. Conversely, a sudden rise in blood pressure due to excitation during the daytime can cause tearing of the blood vessels resulting in intracranial hemorrhage. Cerebrovascular disease primarily affects people who are elderly or have a history of diabetes, smoking, or ischemic heart disease. The results of cerebrovascular disease can include a stroke, or occasionally a hemorrhagic stroke. Ischemia or other blood vessel dysfunctions can affect the person during a cerebrovascular accident.

Classification

A transient ischemic attack (TIA) leaves little to no permanent damage within the brain. The symptoms of this include facial weakness, visual impairment, loss of coordination, or balance and a sudden headache. Severe blockage of the arteries to the brain is known as carotid stenosis. This generally results from high head trauma.

Stroke

Carotid artery effects retina, cerebral hemisphere, or both. Retinal Transient blackouts; the sense of a shade pulled over the eyes. Cerebral Contralateral (opposite sided) paralysis of a single body part; paralysis of one side of the body; localized tingling, numbness; hemianopic visual loss; aphasia (loss of speech); rare loss of consciousness. Vertebrobasilar Bilateral visual disturbance including dim, gray, or blurred vision or temporary total blindness; diplopia (double vision). Labyrinth/medulla Vertigo; unsteadiness; nausea; vomiting. Brainstem Slurring dysarthria (tongue weakness causing impaired speech); dysphagia (difficulty swallowing); numbness, weakness; all four limb paresthesia; drop attacks from sudden loss of postural tone are basilar in origin; a vertebrobasilar artery occlusion episode causes symptoms to be induced by abrupt position changes.

Causes

Cerebrovascular disease can be divided in to embolism, aneurysms, and low flow states depending on its cause.

Major modifiable risk factors include hypertension, smoking, obesity, and diabetes.

Pathophysiology

In a healthy, anatomical structure of the body, the carotid arteries form the main blood supply to the brain. Following a stroke, voluntary control of the muscles may be lost, depending on the type of stroke the victim is encountering. Strokes can also result from embolism or due to a ruptured blood vessel. Embolism blocks small arteries within the brain, causing dysfunction to occur. Spontaneous rupture of a blood vessel in the brain causes a hemorrhagic stroke.

Another form of cerebrovascular disease includes aneurysms. In females with defective collagen, the weak branching points of arteries give rise to protrusions with a very thin covering of endothelium that can tear to bleed easily with minimal rise of blood pressure. This can also occur with defective capillaries caused by tissue cholesterol deposition especially in hypertensive subjects with or without dyslipidemia. If bleeding occurs in this process, the resulting effect is a hemorrhagic stroke in the form of subarachnoid hemorrhage, intracerebral hemorrhage or both.

In the main structure, the carotid arteries overspread the majority of the cerebrum. The common carotid artery divides into the internal and the external cartoid arteries. The internal carotid artery becomes the anterior cerebral artery and the middle central artery. The ACA transmits blood to the frontal parietal and a small part of the occipital lobe. The MCA is the largest branch of the internal carotid artery. From the Basillar artery are two posterior cerebral arteries. Branches of the Basillar and PCA supply the occipital lobe, brain stem, and the cerebellum.

Ischemia is the loss of blood flow to the focal region of the brain. The beginning process of this is quite rapid. The duration of a stroke is usually two to fifteen minutes. One side of the face, hand, or arm may swell up. During this time, the person may lose conscious control and faint. Brain deficits may improve over a maximum of 72 hrs. Deficits do not resolve in all cases. The neurological recovery period includes stable, to improving, brain function. Stable is the period by which neither nutrient supply is regained, nor is it lost. Improving, depending on a hospital code, generally means that the arteries gain control and blood flow functions consistently within the brain. The cartoid arteries connect to the vertebral arteries. These branch off into the cerebellar and posterior meningenial arteries, which supply the back of the brain.

Also, during ischemia, interneurons weaken, causing an insufficient amount to perform vital functions to be present. The neuroglis become congested or maintain loss during a cerebrovascular accident. If impulse amount ceases, then life itself will cease and the victim may enter the stage of clinical death. Neural pathways weaken, therefore decreasing action potential. The neural arc, which in general consists of sensory and motor neurons, weaken as well. The muscles become paralyzed, in some cases for life. Paralysis also includes the weakening of the receptors in the body, unless improvement is made. Cerebrovascular damage to the brain is what makes it difficult for receptors to receive the impulse and transmit it of a neuron. This chemical reaction is then transmitted creating a poor reflex to the body. The meninges that also protect the brain and spinal cord are deeply weakened, allowing the victim to suffer vast transmission of diseases or unstable growth or maintenance if the victim is not in resting position.

During the stage of paralysis, the spinal tracts do not have much to do with the enduring condition of cerebrovascular disease, either, in time may shorten the life of a victim who is suffering because the nutrient supply is weakened in transmission during cerebrovascular disease. Descending and ascending tracts will generally be cut off during cerebrovascular disease, which conduct impulses down from the cord of the brain. This is known as anesthesia in a minor case.

In a healthy body, the cerebrospinal fluid (also known as CSF) may also weaken the cortoid plexus, into a network of brain capillaries. Certain types of hydrocephalus ("water" or CSF on the brain) may be treated by using a shunt (medical) or a cerebral shunt, which involves inserting a hollow tube (or the shunt) through a blocked channel so the CSF can be used to be drained to another portion of the body. The dermatomes are a skin surface area which is regulated by the spinal cord. During a stroke, these may be damaged.

Epidemiology

The most common forms of cerebrovascular disease are cerebral thrombosis (40% of cases) and cerebral embolism (30%), followed by cerebral hemorrhage (20%).^[2]

References

1. ↑ "WHO Disease and injury country estimates". World Health Organization. 2009. Retrieved Nov. 11, 2009.  Check date values in: |access-date= (help)
2. ↑ Page 117 in: Henry S. Schutta; Lechtenberg, Richard (1998). Neurology practice guidelines. New York: M. Dekker. ISBN 0-8247-0104-6. CS1 maint: Multiple names: authors list (link)