Definition and etiology
The term originates from the Latin word infarcire, which translates as "to stuff" or "to cram." Essentially, an infarction represents vascular (or circulatory) necrosis. This means that tissue or a part of an organ dies due to an acute disruption of blood supply.
The main etiological factors causing this condition include:
- Thrombosis;
- Embolism;
- Prolonged arterial spasm.
Morphology and shape of the focus
The external appearance and shape of the necrotic zone directly depend on angioarchitecture—the structural features of the vascular system in a specific organ—as well as the presence of anastomoses and collaterals.
- Triangular (conical, wedge-shaped) form. Typical for organs with a trunk (main-vessel) type of vascular branching.
- Irregular form. Found in organs with a dispersed or mixed type of vascular branching.
According to the type of developing necrosis, infarctions are divided into coagulative (characteristic of most organs, particularly the kidneys) and colliquative (less common, typical of the brain).
Classification by macroscopic appearance
Depending on the macroscopic picture, several types of infarction are distinguished:
- White (ischemic, bloodless). Occurs with the complete cessation of blood flow in the feeding artery or its branch. Most commonly localized in the spleen, brain, and heart.
- Ischemic with a hemorrhagic rim. Typical localization is the myocardium and kidneys. This feature is due to the presence of a large number of vascular collaterals and anastomoses. Because of this, the demarcation zone occupies a significant area and acquires a pronounced red-brown color.
- Red (hemorrhagic). Develops when arteries (less frequently, veins) are occluded in the lungs, intestines, ovaries, and brain. Two conditions are necessary for its occurrence: a dual blood supply to the organ and the presence of venous congestion.
- Red (venous) infarction of the spleen. A rare variant (usually, splenic infarction is white). Occurs upon thrombosis or obstruction of the splenic vein. The necrotic zone becomes engorged with blood, turns dark red or black, and the demarcation zone is not prominent (washed out).
Pathogenesis of hemorrhagic pulmonary infarction
The mechanism of development of a red infarction using lung tissue as an example is as follows:
- Obstruction of a pulmonary artery branch occurs (by a thrombus or thromboembolus).
- Blood pressure drops sharply in the basin of the occluded artery.
- Blood rushes via anastomoses from the bronchial artery system (where the high-pressure zone is maintained) into the low-pressure zone.
- Capillaries of the interalveolar septa rupture, and the tissue becomes impregnated with blood.
Evolution and outcomes
After 24 hours, the necrotic zone becomes clearly visible, acquiring a pale yellowish or pale brownish color. A demarcation zone forms between it and the healthy tissue. Histologically, it consists of an inflammatory infiltrate (leukocytes and macrophages), hyperemic vessels, and areas of diapedesis of blood cells (up to small hemorrhages).
Outcomes are divided into two groups:
1. Favorable:
- Organization (scarring). In the first days, segmented neutrophils and macrophages partially resorb (dissolve) the necrotic tissue. On days 7–10, granulation tissue begins to grow in from the demarcation zone. Gradually, it replaces the necrotic zone, matures, and turns into a scar.
- Cyst formation. Formation of a cavity (sometimes filled with fluid) at the site of colliquative necrosis (often observed in the brain).
- Glial scar. Replacement of the defect with glial tissue. This outcome is characteristic of small-sized ischemic brain infarctions.
2. Unfavorable:
- Suppuration. Purulent melting of the infarction zone occurs (septic disintegration).
Briefly: answers to topical questions
In which organs does infarction have a wedge shape?
An infarction has a wedge-shaped (triangular, conical) form in organs with a trunk-type vascular branching and poorly developed collaterals.
- Spleen (lien) — trunk type of branching
- Kidney (ren) — trunk type of branching
- Lung (pulmo) — trunk type of branching
In which organs does infarction have an irregular shape?
An infarction has an irregular shape in organs with a dispersed or mixed type of vascular branching.
- Myocardium (myocardium) — dispersed/mixed type of branching
- Brain (encephalon) — dispersed/mixed type of branching
How does coagulative infarction differ from colliquative infarction?
Coagulative and colliquative infarctions differ in tissue consistency, fluid content, and typical localization.
| Sign | Coagulative | Colliquative |
|---|---|---|
| Consistency | dense and dry | flabby, soft |
| Fluid content | low | high fluid content |
| Frequency | characteristic of most organs | occurs less frequently |
| Localization | kidney, heart | brain (focus of gray softening) |
What stages of myocardial infarction development are distinguished over time?
Three stages of myocardial infarction development are distinguished over time.
- Ischemic (pronecrotic) stage — 0–18–24 hours; metabolic disorders increase, energy deficiency develops; macroscopic changes may not be visible.
- Necrotic stage — 24 hours to several days; cardiomyocytes show signs of necrobiosis and coagulative necrosis, surrounded by a demarcation zone with leukocytic (neutrophilic) infiltration.
- Stage of organization (scarring) — 7 days and later; resorption of necrotic masses occurs, ingrowth of granulation tissue begins. In the 2nd week, granulation tissue formation starts; by the 3rd week, the necrotic zone is almost completely replaced by maturing granulation tissue; in weeks 4–6, granulations turn into mature connective tissue. Complete organization of the infarct and adaptation are completed in 2–2.5 months.
To remember the conditions for a red (hemorrhagic) infarct, use the "Two V's" rule: Venous congestion + Vascular dual supply (second blood source).
Class and exam questions
What determines the shape of an infarct?
On the angioarchitecture (vascular system structure) of the organ. Main vessels produce a wedge-shaped form, while dispersed or mixed vessels result in an irregular shape.
Why does myocardial infarction have a hemorrhagic rim?
Due to the presence of a large number of vascular collaterals and anastomoses, which form a wide red-brown demarcation zone around the focus of necrosis.
Which cells react first in the necrosis zone?
In the first days, segmented neutrophils and macrophages accumulate in the demarcation zone, beginning to resorb (clear) the dead tissue.
What else to study on this topic
- Histological differences between coagulative and liquefactive necrosis
- Step-by-step pathogenesis of hemorrhagic pulmonary infarction
- Stages of infarct organization: from granulation tissue to scar
- Features of demarcation zone formation in various organs
- Rare forms: red venous splenic infarction
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