Infarction

In medicine, infarction refers to tissue death (necrosis) that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.

Causes
The supplying artery may be blocked by an obstruction (e.g. an arterial embolus, thrombus, or atherosclerotic plaque), may be mechanically compressed (e.g. tumor, volvulus, or hernia), ruptured by trauma (e.g. atherosclerosis or vasculitides), or vasoconstricted (e.g. cocaine vasoconstriction leading to myocardial infarction).

Hypertension and atherosclerosis are risk factors for both atherosclerotic plaques and thromboembolism. In atherosclerotic formations, a plaque develops under a fibrous cap. When the fibrous cap is degraded by metalloproteinases released from macrophages or by intravascular shear force from blood flow, subendothelial thrombogenic material (extracellular matrix) is exposed to circulating platelets and thrombus formation occurs on the vessel wall occluding blood flow. Occasionally, the plaque may rupture forming an embolus that travels with the blood flow downstream where the vessel narrows and eventually clogs the vessel lumen.

Infarctions can also involve mechanical blockage of the blood supply, such as when part of the gut or testicles herniates or becomes involved in a volvulus.

By histopathology
Infarctions are divided into 2 types according to the amount of blood present:
 * White infarctions (anemic infarcts) affect solid organs such as the spleen and kidneys wherein the solidity of the tissue substantially limits the amount of nutrients (blood/oxygen/glucose/fuel) that can flow into the area of ischemic necrosis. Similar occlusion to blood flow and consequent necrosis can occur as a result of severe vasoconstriction as illustrated in severe Raynaud's phenomenon that can lead to irreversible gangrene.
 * Red infarctions (hemorrhagic infarcts), generally affect the lungs or other loose organs (testis, ovary, small intestines). The occlusion consists more of red blood cells and fibrin strands. Characteristics of red infarcts include: occlusion of a vein; loose tissues that allow blood to collect in the infarcted zone; tissues with a dual circulatory system (lung, small intestines); tissues previously congested from sluggish venous outflow; and reperfusion (injury) of previously ischemic tissue that is associated with reperfusion-related diseases such as - Myocardial infarction, stroke (cerebral infarction), shock-resuscitation, replantation surgery, frostbite, burns and organ transplantation.

By localization

 * Heart: Myocardial infarction (MI), commonly known as a heart attack, is an infarction of the heart, causing some heart cells to die. This is most commonly due to occlusion (blockage) of a coronary artery following the rupture of a vulnerable atherosclerotic plaque, which is an unstable collection of lipids (fatty acids) and white blood cells (especially macrophages) in the wall of an artery. The resulting ischemia (restriction in blood supply) and oxygen shortage, if left untreated for a sufficient period of time, can cause damage or death of heart muscle tissue (myocardium).


 * Brain: Cerebral infarction is the ischemic kind of stroke due to a disturbance in the blood vessels supplying blood to the brain. It can be atherothrombotic or embolic. Stroke caused by cerebral infarction should be distinguished from two other kinds of stroke: cerebral hemorrhage and subarachnoid hemorrhage. Cerebral infarctions vary in their severity with one third of the cases resulting in death.


 * Spleen: Splenic infarction occurs when the splenic artery or one of its branches are occluded, for example by a blood clot. Although it can occur asymptomatically, the typical symptom is severe pain in the left upper quadrant of the abdomen, sometimes radiating to the left shoulder. Fever and chills develop in some cases. It has to be differentiated from other causes of acute abdomen.


 * Limb: Limb infarction is an infarction of an arm or leg. Causes include arterial embolisms and skeletal muscle infarction as a rare complication of long standing, poorly controlled diabetes mellitus. A major presentation is painful thigh or leg swelling.


 * Bone: Infarction of bone results in avascular necrosis. Without blood, the bone tissue dies and the bone collapses. If avascular necrosis involves the bones of a joint, it often leads to destruction of the joint articular surfaces (see osteochondritis dissecans).


 * Testicle: an infarction of a testicle may be caused by testicular torsion.

Associated diseases
Diseases commonly associated with infarctions include:
 * Peripheral artery occlusive disease (the most severe form of which is gangrene)
 * Antiphospholipid syndrome
 * Sepsis
 * Giant-cell arteritis (GCA)
 * Hernia
 * Volvulus