Infarction of the Brain

**kellyhound** · #1 ● 11-16-2014, 07:09 AM

Infarction and ischaemia of the brain are closely associated with conditions that lead to focal necrosis of the nervous tissue in the ischaemic area, usually corresponding to the distribution of an arterial vessel.

The main causes of infarction are atherosclerotic occlusion of large vessels, embolic occlusion of distal vessels, vasculitis and arterial spasm following subarachnoid haemorrhage.

The common clinical presentation is stroke, with different neurological syndromes according to the functions located in the involved region.

From dense unilateral hemiplegia to focal aphasias, from sudden coma to hemianopia, from hemispheric cerebellar ataxia to diplopia, from a Wallenberg syndrome to hemiballism, almost any neurological syndrome may be produced by a focal ischaemia with infarction of the brain tissue.

Ischaemia is a prerequisite of infarction but may still be reversible; if permanent, irreversible damage to the nervous tissue results.

Not all the ischaemic nerve cells die and different cell types have varying sensitivity to ischaemia; in an ischaemic region a peripheral area of so-called "penumbra" is usually present, in which cells remain viable for several hours but at risk if circulation is not re-established.

Neurones are the most sensitive to ischaemia, followed by astrocytes, oligodendroglia, microglia and endothelial cells. When a vessel is occluded, the entire supplied region does not become ischaemic because efficient collateral circulation may develop very rapidly, if not immediately.

This happens through anastomoses that are either permanently or potentially patent; the circle of Willis and the external-internal carotid arteries anastomoses are examples of permanent and efficient collateral circulation, while the cortico-cortical anastomoses are an example of collateral circulation that opens up when the arterial pressure drops on one side.

Some deep areas of the brain are border zones between the terminal capillary beds of the major cerebral arteries in the cortex and receive the lowest cerebral blood flow; these zones, called watershed areas, are the first to suffer ischaemia and infarction during generalized systemic hypotension.