What does necrosis mean?
Necrosis is a type of cell death. It is an uncontrolled type of cell death that happens before the end of the natural life span of the cell. Pathologists use the word necrotic to describe a large area of tissue that has died of necrosis. Another common type of cell death is called apoptosis.
What causes a cell to die by necrosis?
Anything that injures a cell can cause it to die by necrosis. The most common causes are exposure to a toxin, infection, loss of blood flow, and trauma.
Loss of blood flow injures a cell by depriving it of oxygen and glucose, both of which are needed for a cell to function normally. Doctors use the word ischemia to describe a tissue that has lost its blood flow.
Cancer cells commonly die by necrosis. As a result, necrosis is often used by pathologists to support the diagnosis of a malignant (cancerous) tumour. More aggressive or higher grade tumours are also more likely to show necrosis compared to less aggressive or low grade tumours. In addition to necrosis, pathologists look for other features such as atypia and mitoses to support the diagnosis of cancer.
Patterns of necrosis
Some patterns of necrosis are only seen in specific situations. These patterns of necrosis are given special names and you may see them used in your pathology report.
- Tumour type – This pattern is commonly seen in fast growing tumours. As the number of cells in the tumour increase, some areas of the tumours are unable to get enough blood flow and the cells in that area quickly die.
- Necrosis in a granuloma – A granuloma is a collection of specialized immune cells including lymphocytes and histiocytes. It is a type of chronic inflammation. Necrosis is commonly seen in granulomas caused by infections such as tuberculosis. In this situation, the necrosis is seen in the centre of the granuloma, surrounded by immune cells. This pattern of necrosis is often described as a necrotizing granuloma or necrotizing granulomatous inflammation.
- Ischemic type – This pattern typically happens when a blood vessel becomes blocked and blood flow is cut off to the tissue around it. Another word for ischemic type necrosis is an infarct. This pattern of necrosis is commonly seen in the heart after a heart attack or in the brain after a stroke.
- Caseous – This pattern is often caused by an infection such as tuberculosis. The word caseous is used to the describe the white appearance of the tissue when it is examined without a microscope. When examined under the microscope, granulomas are often seen in areas of caseous necrosis.
- Gangrenous – This pattern can be caused by loss of blood flow to a tissue or bacterial infection. Dry gangrene is sometimes used to describe the change caused by decreased blood flow while wet necrosis is used to describe the change caused by bacterial infections.
- Fat – This pattern is used to describe the death of specialized fat cells called adipocytes. This pattern can happen anywhere in the body where fat cells are normally found.
- Fibrinoid – This pattern is seen when cells from the immune system damage a blood vessel. In this case, the necrosis involves the wall of the blood vessel which makes it look bright pink when examined under the microscope.