Infarction

• Definition of an infarction & necrosis
• List the main causes of infarction
• Describe the typical appearances of infarcts
• Describe the sites of infarct with particular reference to:
  • Cerebral infarcts
  • Myocardial infarcts
  • Intestinal infarcts
  • Renal & splenic infarct

Necrosis –

A spectrum of visible changes that follow cell death in living tissue, resulting from the progressive action of enzymes on the lethally injured cells.

Infarct –

An area of ischaemic necrosis due to occlusion of the arterial supply or venous drainage of a tissue.

The 2 most important causes are thrombosis and thromboembolism. 

Other (minor) causes include –

• Vasospasm
• Compression of a vessel
• Torsion of a vessel by twisting around on itself
• Traumatic rupture
• Expansion of an atheroma

Anaemic (white) infarcts are quite common. They occur due to arterial occlusion and are most commonly found in solid organs (spleen, kidney, heart).

Below is a picture of an anaemic infarct of the kidney. Note the wedge shape of the infarct with the base of the apex lying outwards and the apex centrally. This shape correlates with the arterial blood supply of the kidney.

A similar pattern of infarction is seen in the spleen.

Red (haemorrhagic) infarcts occur due to venous occlusion or embolism in organs with a dual blood supply.

Below is a picture of an intestinal infarct (note some normal loops of bowel). It is red in colour because the small intestine has a dual blood supply.

A septic infarct develops when the material that embolises from one site to a distant site contains infected material so that infection is set up in the infarct in the distant site.

Septic infarcts can develop, for example, after endocarditis, when a vegetation on a heart valve containing bacterial breaks off as an embolus and is carried off to, for example, the fingers or toes or elsewhere. The patient gets septic infarcts in which the bacteria grow to form abscesses.

Below is a diagram of a coronal slice of the right cerebral hemisphere. Sometimes the brain shows multiple small infarcts in the areas between the territories of the different arteries (i.e between the territory of the middle cerebral artery and the anterior cerebral artery).

This is due to global reduced blood flow or hypoperfusion.

The idea is that the tissue at the periphery of the area supplied by any artery is the most prone to hypoxia, as it’s the last to receive its oxygen.

These “boundary areas” happen to coincide in the regions between two arterial territories. So if the blood pressure drops, for any reason, then these zones tend to become infarcted.

As this is analogous to the areas between the territories drained by rivers, the name watershed was applied.

Below is an image of an anterolateral myocardial infarction. Note the pale infarcted tissue on the anterior surface of the left ventricle and interventricular septum.

This type of necrosis is called coagulative necrosis. The tissues retain their architecture after they die. This type of necrosis is also found in the kidney, bowel and leg.

Cerebral infarction occurs when the blood supply to the brain is reduced. This often occurs due to an embolus originating from the carotid arteries. It clinically presents as a stroke and the symptoms depend on the territory affected.

Pulmonary infarction usually occurs with a medium-large sized embolus which travels down the pulmonary tree and obstructs a medium-sized pulmonary artery branch. If the patient has any underlying cardiovascular disease it will lead to hypoperfusion of the lung parenchyma resulting in infarction. This would clinically present with haemoptysis.

There are other factors, such as the existence of an alternative blood supply, as for instance in the lung and liver. Congestive cardiac failure, too, predisposes to infarction, as the tissues are already underperfused.

Infarction is a very important pathological process.

It is important that you understand the causes and classification of infarcts and the morphology of infarcts in the main organs affected by it.