Form Of An Embolism Or Thrombosis Biology Essay

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Ischaemic stroke is the most common form of stroke and is normally quoted as occurring in about 80 of stroke cases however this may be an overestimate with actual rates below this(1). It is typically the result of impaired cerebral blood flow caused by a blood clot occluding a cerebral vessel.

This can occur in the form of an embolism or thrombosis. Thrombosis can be classified into two groups; large vessel (involving carotid arteries) or small vessel (involving Circle of Willis and posterior circulation). Atheroma, a degenerative disease of medium to large arteries, is a common cause of thrombosis and can cause vessel stenosis, vessel weakness and ulceration possibly leading to thrombus formation by activation of the extrinsic clotting pathway. Emboli most commonly arise from the heart, extracranial arteries or rarely from the right side circulation. Cardiac emboli arise from valvular thrombosis (e.g. mitral Stenosis), mural thrombosis (e.g. atrial fibrillation) and atrial myxoma (benign atrial tumour). Less commonly ischaemic stroke can be the consequence of systemic hypoperfusion known as a watershed stroke, for example during shock.

Haemorrhagic stroke is caused when a weakened blood vessel ruptures, either within the brain (intracerebral) or on the surface so that blood leaks into area between brain and skull (subarachnoid).

The rupture of intracerebral blood vessels can be classified as either a primary or secondary intracerebral haemorrhage. Primary intracerebral haemorrhages (PIH) are spontaneous with no single cause. Hypertensive arteriosclerosis and amyloid angiopathy account for 80% of PIH(2). The causative factors can be categorized into three groups; anatomical factors (malformation of vasculature), haemodynamic factors (blood pressure) or haemostatic factors (platelet and coagulation dysfunction. Secondary intracerebral haemorrhage (SIH) is due to underlying weaknesses in blood vessels or coagulability normally due to genetic conditions. Subarachnoid haemorrhage is typically the result of rupture aneurysms.

Other types

Cerebral venous sinus thrombosis (CVST) is caused typically by thrombosis, about 80%, in the superior sagittal and lateral sinuses(3). CVST, like PIH, is the consequence of a collection of causative factors however unlike PIH it tends not be caused by vessel wall damage but more commonly caused by Factor V Leiden mutation, a genetic coagulation disorder, or unknown factors accounting for 25% of cases(3).

Spinal cord infarction occurs by occlusion, either of the arterial or venous system, of the vessels supplying the spinal cord. Occlusion of the anterior spinal artery is more common and is normally caused by arteriosclerosis. Posterior spinal artery and venous infarctions are less common.(4)

Figure 1 Stroke classification-

Transient Ischemic Attack (TIA)

A TIA is a temporary (transient) interruption of blood flow to the brain which occurs for less than 24 hours with no lasting neurological dysfunction. This indicates a high risk of a full stroke.

Stroke Classification

Etiological Classification

The Trial of Org Acute Stroke Treatment (TOAST)(5) etiologically classified ischaemic stroke into 5 categories; large-artery atherosclerosis, cardioembolism, small-vessel occlusion (lacunae), stroke of other determined etiology and stroke of undetermined etiology. Classification is based on clinical presentation, imaging studies; brain (CT/MRI), cardiac (echocardiography) and duplex extracranial arteries (arteriography) and laboratory assessment of prothrombotic state. The features of each stroke subtype are listed in table 1.

Table 1: Features of TOAST stroke classification

Stroke subtype

Features

Large-artery atherosclerosis

Cardioembolism

Small-vessel occlusion (lacunae)

Stroke of other determined etiology

Stroke of undetermined etiology

Clinical

Cerebral cortical or cerebellar dysfunction

+

+

-

+/-

+/-

Lacunar syndromes

-

-

+

-

+/-

Imaging

Cortical, cerebellar, brain stem, subcortical infarcts > 1.5cm diameter

+

+

-

+/-

+/-

Brainstem or cortical lesion <1.5 cm diameter

-

-

+

+/-

+/-

History

Diabetes mellitus and/or hypertension

-

-

+

+/-

+/-

TIA

+

+

-

+/-

+/-

Tests

Stenosis of extracranial internal carotid artery

+

-

-

-

+/-

Cardiac source of embolus

-

+

-

-

+/-

Other abnormal test

-

-

-

+

+/-

Clinical Classification

Bamford et al(6) in the Oxford Community Stroke Project (OCSP)classified ischaemic stroke into 4 different sub groups based on a population study of the participant's first stroke. Patients in the study were divided into 4 sub groups; lacunar infarct (LACI), total anterior circulation infarct (TACI), partial circulation infarct (PACI) and posterior circulation infarct (POCI), after hemorrhagic stroke had been ruled out by CT scan. The OSCP is a simple, reliable and rapid way of categorizing ischaemic stroke; the categories can be used to predict CT scan findings, outcome and functional recovery. (7, 8) The different sub groups are linked to ischaemia in different cerebral arteries; middle cerebral artery ischaemia causing TACI and PACI, perforating artery causing LACI and posterior cerebral artery causing POCI. TACI is defined by higher dysfunction (dysphasia, visuospatial, dyscalculia), homonymous hemianopia and ipsilateral motor and/or sensory deficit in 2 or 3 of the face, arm or leg. PACI is defined by any one of; two out of three of TACI, higher dysfunction alone or limited motor or sensory deficit. LACI defined as the presence of any one of the clinical lacunar syndrome but without new dysphasia, new visuospatial problem, proprioceptive sensory loss, vertebrobasilar features. POCI defined by any of these features cranial nerve palsy and contralateral motor or sensory deficit, bilateral motor or sensory deficit, conjugate eye movement problems, cerebellar dysfunction without ipsilateral long tract signs and isolated homonymous hemianopia.(9) MORTALITY RATES

Outcome

The outcome of stroke can be assessed by many different scales, the more commonly used scales are the Barthel index (BI) and the modified Rankin scale (mRs)(10).

Barthel Index

The Barthel index measures the patient's performance in 10 activities of daily living, which are divided into two groups; self care (feeding, grooming, bathing, dressing, bowel and bladder continence and toilet use) and mobility (ambulation, transfers and stair climbing). The maximal score is 100 and indicates a fully independent patient, a score of 0 representing a totally independent bed ridden patient.

Modified Rankin Scale

The mRs was originally introduced in 1957(11) by Rankin and was then later modified(12). The mRs measures independence of the patient rather than task related performance and so includes both mental and physical adaptations to the neurological deficits(10). The scale ranges from 0 - 6; 0 a patient with no symptoms, 5 most severe disability and 6 death.

Quality of Life

Quality of life is an important part of patient recovery and needs to be considered as quality of life gives a patient's perspective on his outcome. One of the frequently used quality of life measures is the EuroQuol questionnaire and has been shown to be a reliable and valid measure.(13)

EuroQuol

The EuroQuol was released in 1990 and is designed to be completed by the respondent. The EuroQuol has six parts; the first five examine the respondent's view on mobility, self-care, usual activities, pain or discomfort and anxiety or depression. Each part can be awarded 3 points leading to a possible 243 health states. The final part of the EuroQuol asks the respondent to mark their current health state on scale of 0 (worst imaginable health state) and 100 (best imaginable health state).(14)

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