Stroke

STROKE:

A stroke 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 supply) caused bythrombosisor embolism or due to a hemorrhage. 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 inability to see one side of the visual field.[1] In the past, stroke was referred to as cerebrovascular accident or CVA, but the term “stroke” is now preferred.[citation needed]

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CT scan slice of the brain showing a right-hemispheric ischemic stroke (left side of image).

A stroke is a medical emergency and can cause permanent neurological damage, complications, and death. It is the leading cause of adult disability in the United States and Europe. In the UK, it is the second most common cause of death, the first being heart attacks and third being cancer. It is the number two cause of death worldwide and may soon become the leading cause of death worldwide.[2] Risk factors for stroke include advanced age, hypertension (high blood pressure), previous stroke ortransient ischemic attack(TIA), diabetes, high cholesterol, cigarette smoking and atrial fibrillation.[3] High blood pressure is the most important modifiable risk factor of stroke.[1]

A stroke is occasionally treated with thrombolysis (“clot buster”), but usually with supportive care (speech and language therapy, physiotherapyand occupational therapy) in a “stroke unit” and secondary prevention with antiplatelet drugs (aspirin and often dipyridamole), blood pressure control, statins, and in selected patients with carotid endarterectomy and anticoagulation.[1]

Classification

Strokes can be classified into two major categories: ischemic and hemorrhagic. Ischemia is due to interruption of the blood supply, while hemorrhage is due to rupture of a blood vessel or an abnormal vascular structure.

80% of strokes are due to ischemia; the remainder are due to hemorrhage. Some hemorrhages develop inside areas of ischemia (“hemorrhagic transformation”). It is unknown how many hemorrhages actually start off as ischemic stroke.[1]

Ischemic stroke

[A slice of brain from the autopsy of a person who suffered an acutemiddle cerebral artery (MCA) stroke]

In an ischemic stroke, blood supply to part of the brain is decreased, leading to dysfunction of the brain tissue in that area. There are four reasons why this might happen:

1. Thrombosis (obstruction of a blood vessel by a blood clot forming locally)

2. Embolism (idem due to an embolus from elsewhere in the body, see below),[1]

3. Systemic hypoperfusion (general decrease in blood supply, e.g. in shock)[6]

4. Venous thrombosis.[7] Stroke without an obvious explanation is termed “cryptogenic” (of unknown origin); this constitutes 30-40% of all ischemic strokes.[1][8]

There are various classification systems for acute ischemic stroke. The Oxford Community Stroke Project classification (OCSP, also known as the Bamford or Oxford classification) relies primarily on the initial symptoms; based on the extent of the symptoms, the stroke episode is classified as total anterior circulation infarct (TACI), partial anterior circulation infarct (PACI), lacunar infarct (LACI) or posterior circulation infarct(POCI). These four entities predict the extent of the stroke, the area of the brain affected, the underlying cause, and the prognosis.[9][10]The TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification is based on clinical symptoms as well as results of further investigations; on this basis, a stroke is classified as being due to (1) thrombosis or embolism due to atherosclerosis of a large artery, (2) embolism of cardiacorigin, (3) occlusion of a small blood vessel, (4) other determined cause, (5) undetermined cause (two possible causes, no cause identified, or incomplete investigation).[1][11]

Hemorrhagic stroke

[CT scan showing an intracerebral hemorrhage with associated intraventricular hemorrhage.]

Intracranial hemorrhage is the accumulation of blood anywhere within the skull vault. A distinction is made between intra-axial hemorrhage(blood inside the brain) and extra-axial hemorrhage (blood inside the skull but outside the brain).

Intra-axial hemorrhage is due to intraparenchymal hemorrhage or intraventricular hemorrhage (blood in the ventricular system). The main types of extra-axial hemorrhage are epidural hematoma (bleeding between the dura mater and the skull), subdural hematoma (in the subdural space) andsubarachnoid hemorrhage (between the arachnoid mater and pia mater). Most of the hemorrhagic stroke syndromes have specific symptoms (e.g. headache, previous head injury).Intracerebral hemorrhage (ICH) is bleeding directly into the brain tissue, forming a gradually enlarging hematoma (pooling of blood).[citation needed]

Signs and symptoms

Stroke symptoms typically start suddenly, over seconds to minutes, and in most cases do not progress further. The symptoms depend on the area of the brain affected. The more extensive the area of brain affected, the more functions that are likely to be lost. Some forms of stroke can cause additional symptoms: in intracranial hemorrhage, the affected area may compress other structures. Most forms of stroke are not associated with headache, apart from subarachnoid hemorrhage and cerebral venous thrombosis and occasionally intracerebral hemorrhage.

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Epidemiology

Stroke could soon be the most common cause of death worldwide.^[100] Stroke is currently the second leading cause of death in the Western world, ranking after heart disease and before cancer,^[2] and causes 10% of deaths worldwide.^[101] Geographic disparities in stroke incidence have been observed, including the existence of a “stroke belt” in the southeastern United States, but causes of these disparities have not been explained.

The incidence of stroke increases exponentially from 30 years of age, and etiology varies by age.^[102] Advanced age is one of the most significant stroke risk factors. 95% of strokes occur in people age 45 and older, and two-thirds of strokes occur in those over the age of 65.^[96][20] A person’s risk of dying if he or she does have a stroke also increases with age. However, stroke can occur at any age, including in fetuses.

Family members may have a genetic tendency for stroke or share a lifestyle that contributes to stroke. Higher levels of Von Willebrand factor are more common amongst people who have had ischemic stroke for the first time.^[103] The results of this study found that the only significant genetic factor was the person’s blood type. Having had a stroke in the past greatly increases one’s risk of future strokes.

Men are 25% more likely to suffer strokes than women,^[20] yet 60% of deaths from stroke occur in women.^[97] Since women live longer, they are older on average when they have their strokes and thus more often killed (NIMH 2002).^[20] Some risk factors for stroke apply only to women. Primary among these are pregnancy, childbirth, menopause and the treatment thereof (HRT).

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References

1. ^ Sims NR, Muyderman H (September 2009). “Mitochondria, oxidative metabolism and cell death in stroke”. Biochimica et Biophysica Acta 1802 (1): 80–91. doi:10.1016/j.bbadis.2009.09.003. PMID 19751827.
2. ^ ^{a b c d e f g h i j k l} Donnan GA, Fisher M, Macleod M, Davis SM (May 2008). “Stroke”. Lancet 371 (9624): 1612–23. doi:10.1016/S0140-6736(08)60694-7. PMID 18468545.
3. ^ Feigin VL (2005). “Stroke epidemiology in the developing world”. Lancet 365 (9478): 2160–1. doi:10.1016/S0140-6736(05)66755-4. PMID 15978910.
4. ^ Stroke Mount Sinai Hospital, New York
5. ^ World Health Organisation (1978). Cerebrovascular Disorders (Offset Publications). Geneva: World Health Organization. ISBN 9241700432. OCLC 4757533.
6. ^ Kidwell CS, Warach S (December 2003). “Acute ischemic cerebrovascular syndrome: diagnostic criteria”. Stroke 34 (12): 2995–8. doi:10.1161/01.STR.0000098902.69855.A9. PMID 14605325.
7. ^ “Brain Basics: Preventing Stroke”. National Institute of Neurological Disorders and Stroke. Retrieved 2009-10-24.