Stroke

A stroke, previously known medically as a cerebrovascular accident (CVA), 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 flow) caused by blockage (thrombosis, arterial embolism), or a hemorrhage (leakage of blood). 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 an inability to see one side of the visual field.

Classification

Strokes can be classified into two major categories: ischemic and hemorrhagic. Ischemic strokes are those that are caused by interruption of the blood supply, while hemorrhagic strokes are the ones which result from rupture of a blood vessel or an abnormal vascular structure. About 87% of strokes are caused by ischemia, and the remainder by hemorrhage. Some hemorrhages develop inside areas of ischemia (“hemorrhagic transformation”). It is unknown how many hemorrhages actually start as ischemic stroke.

Ischemic

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:
Thrombosis (obstruction of a blood vessel by a blood clot forming locally)
Embolism (obstruction due to an embolus from elsewhere in the body, see below),
Systemic hypoperfusion (general decrease in blood supply, e.g. in shock)
Venous thrombosis.

Stroke without an obvious explanation is termed “cryptogenic” (of unknown origin); this constitutes 30-40% of all ischemic strokes.

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. 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 cardiac origin, (3) occlusion of a small blood vessel, (4) other determined cause, (5) undetermined cause (two possible causes, no cause identified, or incomplete investigation).
Hemorrhagic

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) and subarachnoid hemorrhage (between the arachnoid mater and pia mater). Most of the hemorrhagic stroke syndromes have specific symptoms (e.g. headache, previous head injury).

Stroke is diagnosed through several techniques: a neurological examination (such as the Nihss), CT scans (most often without contrast enhancements) or MRI scans, Doppler ultrasound, and arteriography. The diagnosis of stroke itself is clinical, with assistance from the imaging techniques. Imaging techniques also assist in determining the subtypes and cause of stroke. There is yet no commonly used blood test for the stroke diagnosis itself, though blood tests may be of help in finding out the likely cause of stroke.

Imaging


CT scan slice of the brain showing a right-hemispheric ischemic stroke (left side of image).
CT scan showing an intracerebral hemorrhage with associated intraventricular hemorrhage.
Head CT showing deep intracerebral hemorrhage due to bleeding within the cerebellum, approximately 30 hours old, in a 68 year old male patient with a stroke.
Head MRI showing deep intracerebral hemorrhage (cerebellum).

For diagnosing ischemic stroke in the emergency setting:
CT scans (without contrast enhancements)
sensitivity= 16%
specificity= 96%
MRI scan
sensitivity= 83%
specificity= 98%

For diagnosing hemorrhagic stroke in the emergency setting:
CT scans (without contrast enhancements)
sensitivity= 89%
specificity= 100%
MRI scan
sensitivity= 81%
specificity= 100%

For detecting chronic hemorrhages, MRI scan is more sensitive.

For the assessment of stable stroke, nuclear medicine scans SPECT and PET/CT may be helpful. SPECT documents cerebral blood flow and PET with FDG isotope the metabolic activity of the neurons.

Source.

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