Cerebral thrombosis occurs when a
blood clot, or thrombus, forms
within the
brain itself, blocking the flow of blood through the
affected vessel. Clots most often form due to "hardening" (atherosclerosis)
of brain arteries. Cerebral thrombosis occurs most often at night or
early in the morning. Cerebral thrombosis is often preceded by a transient ischemic attack,
or TIA, sometimes called a "mini-stroke." In a TIA, blood flow is
temporarily interrupted, causing short-lived stroke-like symptoms.
Recognizing the occurrence of a TIA, and seeking immediate treatment,
is an important step in stroke prevention.Cerebral
embolism occurs when a blood clot from elsewhere in the circulatory
system breaks free. If it becomes lodged in an artery supplying the
brain, either in the brain or in the neck, it can cause a stroke. The
most common cause of cerebral embolism is
atrial fibrillation, a
disorder of the heart beat. In atrial fibrillation, the upper chambers
(atria) of the heart beat weakly and rapidly, instead of slowly and
steadily. Blood within the
atria is not completely emptied. This
stagnant blood may form clots within the atria, which can then break
off and enter the circulation. Atrial
fibrillation is a factor in about
15% of all strokes. The risk of a stroke from atrial fibrillation can
be dramatically reduced with daily use of anti-coagulant medication.Hemorrhage,
or bleeding, occurs when a blood vessel breaks, either from trauma or
excess internal pressure. The vessels most likely to break are those
with preexisting defects such as an aneurysm. An aneurysm is a
"pouching out" of a blood vessel caused by a weak arterial wall. Brain
aneurysms are surprisingly common. According to autopsy
studies, about 6% of all Americans have them. Aneurysms rarely cause
symptoms until they burst. Aneurysms are most likely to burst when
blood pressure is highest, and controlling blood pressure is an
important preventive strategy.Intracerebral hemorrhage
affects vessels within the brain itself, while subarachnoid hemorrhage
affects arteries at the brain''s surface, just below the protective
arachnoid membrane. Intracerebral hemorrhages represent about 10% of
all strokes, while subarachnoid hemorrhages account for about 7%.In
addition to depriving affected tissues of blood supply, the
accumulation of fluid within the inflexible skull creates excess
pressure on brain tissue, which can quickly become fatal. Nonetheless,
recovery may be more complete for a person who survives hemorrhage than
for one who survives a clot, because the blood deprivation effects are
usually not as severe.Death of brain cells triggers a
chain reaction in which toxic chemicals created by cell death affect
other nearby cells. This is one reason why prompt treatment can have
such a dramatic effect on final recovery.Risk factorsRisk factors for stroke involve age, sex, heredity, predisposing diseases or other medical conditions, and lifestyle choices:Age
and sex. The risk of stroke
increases with increasing age, doubling for
each decade after age 55. Men are more likely to have a stroke than
women.Heredity. Blacks, Asians, and Hispanics all have
higher rates of stroke than do whites, related partly to higher blood
pressure. People with a family history of stroke are at greater risk.Diseases.
Stroke risk is increased for people with diabetes, heart disease
(especially atrial fibrillation), high blood pressure, prior stroke, or
TIA. Risk of stroke increases tenfold for someone with one or more TIAs.Other medical conditions. Stroke risk increases with obesity, high blood cholesterol level, or high red blood cell count.Lifestyle choices. Stroke risk increases with cigarette smoking (especially if combined with the use of oral contraceptives), low level of physical activity, alcohol consumption above two drinks per day, or use of cocaine or intravenous drugs.SymptomsSymptoms
of an embolic stroke usually come on quite suddenly andre at their
most intense right from the start, while symptoms of a thrombotic
stroke come on more gradually. Symptoms may include:blurring or decreased vision in one or both eyessevere headache, often described as "the worst headache of my life"weakness, numbness, or paralysis of the face, arm, or leg, usually confined to one side of the bodydizziness, loss of balance or coordination, especially when combined with other symptoms
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