Veterinary Pathology - Degenerations & Infiltrations



What are degenerations and infiltrations?

  • Degeneration is a change in the structure of a cell

  • Infiltration is the accumulation of a chemical in a cell

They are both caused by a change in cell metabolism.


Why do degenerations and infiltrations matter in pathology?


They matter because the changes in the cell can show that a specific cause is responsible for the changes to the cells or tissues.


Cellular Swelling


Cell swelling is an early change that occurs in most types of acute cell injury. It may be a prelude to more drastic changes, or simply disappear as the cell adapts and repairs the damage.
  1. The mildest form of cellular degeneration

  2. The first stage of cell injury

  3. Can be caused by many things but toxins and lack of oxygen (anoxia) are the most common causes

What do body parts that have experienced cell swelling look like?


  1. Pale

  2. Sometimes there may not be any gross enlargement but there are bulges on the cut surface

  3. There can be limited swelling which can be hard to tell apart from early post-mortem change

To read more about cell swelling and related papers, click here.


Under Histology, the cells look:


  • swollen

  • the cytoplasm can look redder under H&E stain

  • they have a normal nucleus

You would often see cellular swelling in kidney and liver cells.


Things to note about cell swelling:

  • Its reversible

  • You might not notice it because its very like early post-mortem change and can be a passing stage before more serious damage

What is Hydropic Degeneration?


Hydropic degeneration is a form of cloudy swelling when the cells have too much water.


A good example of hydropic degeneration is seen in Foot and Mouth Disease when the virus attacks the epithelium of the tongue and feet and the cells then blow up like a balloon with water containing the virus. The cells swell up and then burst, thereby shedding the virus into the environment.


To read more about hydropic degeneration in foot and mouth disease, click here.


What is Fatty Degeneration or Steatosis?


This is called LIPIDOSIS.


Lipidosis is a disorder of lipid metabolism in body tissues.


Its caused by too many triglycerides being made in the cell, which results in fat globules forming and accumulating in the cytoplasm and therefore the cell swells.


Under the microscope, you will see yellow, swollen cells and the organ will look pale and greasy with rounded edges to its lobes. This happens most often in the liver.


What causes Fatty Change in organs?


  1. Eating too much

  2. Starvation - this is when the body mobilise fat in response to starvation but can't cope with the increase so it stores the excess as fat in the liver

  3. Liptrope derangement - when the liptrope system is out of sync, fat can gather. Lipotropes are chemicals that help take fat from liver cells.

  4. Metabolic derangement - if glucose isn't available the body uses fat for energy and the same as in starvation, the body might not cope with fat mobilisation and stores the excess in the liver

  5. Anoxia is when the tissues don't have enough oxygen and any condition that lessens the supply of oxygen can cause fatty changes in the liver

  6. Toxins - toxins will damage the metabolism of the cells and some toxins can cause fatty change in the liver. These toxins can come from bacteria, fungi, carbon tetrachloride, phosphorus, plant toxins, arsenic and lead.



Hyaline Degeneration


Hyaline degeneration looks like glass or translucent structureless material in the cytoplasm or around the cell. Hyalin means there is no chemical composition.


You will see hyaline degeneration in white muscle disease and when there are renal casts that have resulted from too much protein passing through the kidneys.




Amyloid Infiltration


This is an abnormal starch-like glycoprotein and is produced when there is a chronic process of pus formation. This happens when the agent that provoked the inflammation is difficult to eliminate.

Amyloid interferes with the function of organs, particularly in the kidney where it can be fatal. It cannot be revered. It shows up green when stained.


A good article on amyloidosis in animals can be found here.



Glycogen degeneration


This leads to a build-up of massive amounts of glycogen in the liver, muscles and kidneys. When this happens, cells swell and the normal cell function is affected.

This looks like foamy cytoplasmic vacuoles that look like fat.


Cellular Inclusions


These are peptide chains that are abnormal and are usually linked to a viral infection. Their presence can indicate defective protein synthesis and if they are found in a specific site or cell, they can be used to diagnose a certain disease.


Age, storage diseases and some species of bacteria (Mycobacterium) can cause cellular inclusions too.


For all other pathology posts, click here.