Ischemic necrosis - infarction. Morphogenesis. Types of infarctions - anemic, hemorrhagic. Organ sites. Microscopic & gross pathomorphology
Ischemia is diminished blood flow to the tissue, compromising delivery of substrates for glycolysis. This causes no/very little ATP to be formed, meaning the active transport of the sodium/potassium pumps fails, causing cellular swelling and eventually necrosis along with increase in ROS and resultant damage.
An infarction is obstruction of the blood supply to an organ or tissue (generally by thrombus) causing local tissue death. It is the single word for ischemic necrosis. We can classify infarctions based on their histopathology:
- White infarction - anemic infarcts
- Affects solid organs (e.g. spleen, heart and kidneys
- Solidity limits nutrients that can flow to the area, it is in effect an absolute necrotic process
- Red infarctions - hemorrhagic infarcts
- Generally affect lungs and other loose organs (testis, ovaries, SI)
- Occlusion occurs in loose tissue where some nutrients is able to get through, or in areas with dual circulation (e.g. lung and small intestine)
White (anaemic) infarcts of the spleen: pale, sharply demarcated, wedge-shaped areas with the base at the capsule.
Image: “Healed splenic infarcts” by Narraburra, CC0, via Wikimedia Commons.
We can also divide infarcts based on organ site:
- Heart = Myocardial infarction
- Brain = ischemic stroke
- Lung = pulmonary infarction
- Spleen = splenic infarction
- Limb = limb infarction
Red (haemorrhagic) infarcts of the lung at autopsy: dark red-purple, sharply outlined areas under the pleura, typically after pulmonary embolism.
Image: “AC08-7 pulmonary infarcts” by Dr. Rocke Robertson, CC BY-SA 4.0, via Wikimedia Commons.
Gross presentation is red or white depending on type of infarct, while histological findings show that of ischemic necrosis (coagulative necrosis), in the CNS we see liquefactive necrosis. Eventually inflammation is followed by repair, with granulation tissue and finally a fibrous scar.
Remember: an infarct is typically wedge-shaped – the occluded vessel lies at the apex and the base faces the organ surface, often covered by fibrinous exudate. Microscopically it is coagulative necrosis (liquefactive in the brain) with a hyperaemic, inflamed border; it is replaced by granulation tissue and finally by a collagenous scar.