In mammalian bodies, cells try to adapt to injury as much as they can. When they can no longer adapt, they undergo degeneration and die.

The exact point at which cell injury becomes irreversible is often difficult to determine. Often there are no microscopic or ultrastructural indications that this point has been reached. So it is the degradation that follows cell death that provides many of the features that allow us to determine that a tissue is necrotic and to specify the type of necrosis.

Necrotic tissues vary greatly in appearance, both grossly and histologically. We'll discuss five patterns:

  • Liquefactive necrosis
  • Coagulative necrosis
  • Caseous necrosis
  • Gangrenous necrosis
  • Fat necrosis
The degree of PRESERVATION OF ARCHITECTURE of the original tissue and cells is the most important criteria used to differentiate these types.

This lesion is from the kidney of a dog. What is your diagnosis?

If this animal had lived, this space would have eventually collapsed and/or been filled in with fibrous connective tissue.

One type of tissue is particularly prone to liquefactive necrosis. Do you know what that tissue is?

This is the brain from a horse. What is your lesion diagnosis?
This is the kidney from a horse that was on high doses of non-steroidal anti-inflammatory drugs. What's your diagnosis?
Microscopically, tissue architecture is preserved in cases of coagulative necrosis and the identity of the necrotic cells is still recognizable. The nuclei of necrotic cells have often disappeared. Their cytoplasm is usually homogeneous and acidophilic, due to the COAGULATION of cytoplasmic proteins. It is the coagulation of these proteins that prevents the rapid destruction of the cell by proteases and the development of liquefactive necrosis.
Let's look at some other examples of coagulative necrosis...
This is muscle from a turkey. What is your lesion diagnosis?

This is the section of necrotic skeletal muscle. The dark red stuff in normal while the paler fibers are necrotic.

Only a few viable muscle fibers are left! But the tissue architecture is preserved and we have no difficulty recognizing that the necrotic cells were muscle fibers.

This is a mouse liver. What is your lesion diagnosis?
This is a kidney from a dog with ethylene glycol (antifreeze) poisoning.

The entire renal cortex is pale and granular and the medulla contains several hemorrhages. Since the process is so diffuse, there is no normal tissue to compare with.

Because cortical pallor can be caused by many processes, microscopic examination is required to diagnose necrosis. Microscopic view »

What is gangrene?
This mouse's tail developed dry gangrene secondary to trauma.
Here is another example of gangrenous necrosis. This pig's ear also developed gangrene secondary to frostbite.
This liver is from a sheep. Do you see the lesion? Answer »

This is a case of avian tuberculosis in a bird's spleen.

There is a necrotic focus at the center of the picture. This material is dark staining and homogeneous. Cells are no longer recognizable and tissue architecture is lost.

We can't tell it at this low magnification, but this cellular debris is surrounded by a zone of macrophages.

Caseous necrosis occurs with certain types of bacteria like Corynebacterium pseudotuberculosis and Mycobacterium avium. Neutrophils are unable to digest these bacteria because of their thick waxy coat, so macrophages and multinucleated cells(see arrow) come in to take over. This is called a granuloma.
This is a photograph of a pancreas. What's your diagnosis?

The mesentery attached to this portion of bovine intestine is necrotic and dominated by chalky white to yellow deposits.

The cause of such massive fat necrosis in cattle is often due to an endophyte fungus (Acremomium coenophialum) infecting pasture. It causes ischemia to the fat which causes it to undergo necrosis.

This concludes this lesson.
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