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This section considers the heterogeneous causes of stroke, the classification of strokes into
subtypes depending on cause, and the pathogenesis of ischaemic events.
Introduction
Roughly 71% of strokes are ischaemic, resulting from blockage of a blood vessel as a result of atherosclerotic
plaques or an embolus from another vessel, while most of the remainder (26%) are the result of haemorrhage from
a blood vessel. Haemorrhagic strokes have very high rates of mortality and morbidity. The distinction between
haemorrhagic and ischaemic strokes is critical in stroke diagnosis because both acute and preventative treatments
often carry a risk of haemorrhage, which would be detrimental in the setting of haemorrhagic stroke.
Both ischaemic and haemorrhagic strokes decrease cerebral perfusion pressure and eventually lead to cellular death.
Without adequate blood supply brain cells cannot produce energy, are damaged, and will die if critical thresholds are
reached. When an artery is occluded blood flow on the periphery of the infarct core is usually reduced but is adequate
to avoid structural damage such that function may improve if circulation is restored.
Ischaemic stroke may arise from atherosclerotic large or small cerebral arteries, or may be cardioembolic in origin.
Atherogenesis occurs over the course of several decades during which the lumen of a blood vessel becomes narrowed by
cellular and extracellular substances, and is eventually obstructed as a result of thrombus formation. Emboli may become
detached and cause vascular obstruction at a site distal from the original thrombus. In one study the earliest lesions
of atherosclerosis, fatty streaks, were found in roughly 65% of children aged 12–14 years. These early lesions gradually
progress to clinically relevant lesions, and do so more frequently in people with risk factors such as
hypercholesteraemia, hypertension and cigarette smoking.
A Stroke Is Not a "Heart Attack of the Brain"
The causes of stroke are more heterogeneous than those associated with myocardial infarction (MI):
- Up to 20 % of all strokes are primary haemorrhages,
- Only 20% of ischaemic strokes are due to large artery atherosclerosis,
- 30-40% of such strokes are of unknown cause.
Haemorrhage is a common and devastating complication of ischaemic stroke, but not of MI. Strokes occur in
older patients than MI and the mean age of stroke patients is 65-70. Stroke patients are at greater risk of major
haemorrhagic complications in the future than MI patients (e.g. twice as likely to have major bleeding).
Stroke patients are at higher risk of recurrent stroke than MI and MI patients are at higher risk of recurrent
MI than of stroke.
References:
Sacco et al. Am J Epidemiol 1998; 147 (3): 259-268.
Albers GW. Neurology 2000; 54 (5): 1022-1028.
Antithrombotic Trialists‘ Collaboration. BMJ 2002; 324 (7329): 71-86.
Boden-Albala et al. Neurology 1999; 52: A557.
Okada et al. Stroke 1989; 20 (5): 598-603.
NINDS Investigators. N Engl J Med 1995; 333 (24): 1581-1587. |
