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Necrosis is a term used in medical and pathological contexts to describe the death of cells or tissues due to various factors such as injury, infection, or disease. It is a complex process that occurs when cells are unable to maintain their normal structure and function, leading to their demise. Necrosis can occur in different organs and tissues throughout the body and may have varying causes and manifestations.
	'''Necrosis''' is the death of living tissue after severe cell injury. It is usually linked to disease, loss of blood supply, infection, toxins, trauma, heat, cold, or other damage that overwhelms the cell's ability to recover.

== Types of Necrosis ==
	Necrosis is different from apoptosis, which is a controlled form of cell death used in normal development and tissue maintenance. Necrotic cells lose membrane integrity, swell, break down, and release their contents into surrounding tissue. That release often triggers inflammation.

=== 1. Coagulative Necrosis ===
Coagulative necrosis is the most common type of necrosis and is characterized by the preservation of the tissue architecture, with the affected area appearing firm and pale. It occurs when there is a disruption in blood supply to the tissue, leading to ischemia and subsequent cell death.
	== Mechanism ==
	Cell injury can begin with oxygen shortage, chemical damage, physical injury, infection, immune injury, or failure of energy production. When the damage is severe enough, ion balance fails, water enters the cell, organelles swell, and enzymes begin breaking down cell structures.

=== 2. Liquefactive Necrosis ===
Liquefactive necrosis occurs in tissues with high water content, such as the brain. It is characterized by the rapid dissolution of affected cells, resulting in the formation of a liquid-filled cystic space. This type of necrosis often arises due to infections or inflammatory processes.
	The final appearance depends on the tissue, the cause, and whether infection is present. Pathologists use the pattern of necrosis as a clue to what happened in the tissue.

=== 3. Caseous Necrosis ===
Caseous necrosis is typically associated with granulomatous inflammation, such as in tuberculosis. It is characterized by the formation of a cheesy or friable material within the affected tissue, resulting from the accumulation of dead cells and cellular debris.
	== Main Patterns ==
	Common patterns include:

=== 4. Fat Necrosis ===
Fat necrosis occurs when adipose tissue undergoes necrosis, typically due to trauma or injury. It is characterized by the release of fatty acids and the formation of chalky white deposits within the affected tissue.
	* '''Coagulative necrosis''': tissue structure remains visible for a time after cell death. It is often seen after loss of blood supply in organs such as the heart, kidney, or spleen.
	* '''Liquefactive necrosis''': dead tissue is digested into a liquid or soft mass. It is common in brain infarcts and many bacterial infections.
	* '''Caseous necrosis''': dead tissue has a soft, cheese-like appearance. It is classically linked with tuberculosis and granulomatous inflammation.
	* '''Fat necrosis''': damaged fat tissue breaks down, often after pancreatitis, trauma, or breast injury.
	* '''Fibrinoid necrosis''': immune-related injury affects blood vessel walls, producing a bright pink appearance under routine staining.
	* '''Gangrenous necrosis''': a clinical term usually used for necrotic limbs or digits, especially when poor blood supply is involved. Wet gangrene includes secondary infection.

=== 5. Gangrenous Necrosis ===
Gangrenous necrosis is a term used to describe necrotic tissue that undergoes secondary bacterial infection. It often occurs in extremities, such as the toes or fingers, and is associated with conditions such as diabetes or peripheral vascular disease.
	== Causes ==
	Necrosis may be caused by:

== Causes and Manifestations ==
Necrosis can result from various factors, including:
	* Ischaemia, where tissue does not receive enough blood and oxygen.
	* Infection by bacteria, viruses, fungi, or parasites.
	* Physical trauma, burns, freezing injury, pressure injury, radiation, or electric shock.
	* Chemical injury, including some poisons and drug toxicities.
	* Immune-mediated injury, including some vasculitic and autoimmune processes.

* Ischemia or insufficient blood supply to a particular area
* Physical trauma or injury, such as severe burns or crushing injuries
* Infection by microorganisms, including bacteria, viruses, or fungi
* Toxic exposure to chemicals or drugs
* Autoimmune disorders or immune-mediated reactions
	The same broad process can appear in very different settings. A heart attack, a brain infarct, severe frostbite, a deep infected wound, and acute pancreatitis can all involve necrosis, but the treatment and urgency differ.

The manifestations of necrosis can vary depending on the affected tissue and the underlying cause. Common signs and symptoms may include pain, swelling, discoloration, and loss of function in the affected area. In some cases, necrotic tissue may become infected, leading to additional complications.
	== Clinical Features ==
	Visible necrosis may look black, grey, brown, yellow, pale, or wet depending on the tissue and cause. It may be painful, numb, swollen, malodorous, or associated with loss of function. Internal necrosis is usually detected through symptoms of the underlying disease, imaging, blood tests, surgery, or microscopic examination.

== Diagnosis and Treatment ==
The diagnosis of necrosis often involves a combination of clinical assessment, medical history review, and imaging studies, such as X-rays, computed tomography (CT), or magnetic resonance imaging (MRI). Biopsy or laboratory tests may also be necessary to identify the underlying cause or determine the extent of tissue damage.
	Infection can make necrotic tissue more dangerous because dead tissue has poor blood supply and can support bacterial growth. In some settings, prompt debridement or restoration of blood flow is needed to prevent spread of damage.

Treatment of necrosis depends on the underlying cause and the specific characteristics of the necrotic tissue. In some cases, interventions may focus on removing or debriding the necrotic tissue to promote healing. Additionally, addressing the underlying cause, such as re-establishing blood supply or treating infections, is essential to prevent further tissue damage.
	== Diagnosis and Management ==
	Diagnosis depends on location. Clinicians may use examination, blood tests, imaging, tissue biopsy, microbiology, and surgical assessment. Pathology can confirm the pattern of necrosis and may identify infection, vascular injury, tumour necrosis, or inflammatory disease.

	Management is aimed at the cause. Examples include restoring blood flow after ischaemia, treating infection, removing dead tissue, draining abscesses, controlling diabetes or vascular disease, and supporting wound healing. Necrotic tissue itself cannot be restored to normal living tissue.

	== See Also ==
	* [[Osteoarthritis]]
	* [[Common_Medical_Terms]]
	* [[Adenosine_Triphosphate_(ATP)]]

	== References ==
	* [https://www.cancer.gov/publications/dictionaries/cancer-terms/def/necrosis National Cancer Institute: Necrosis definition]
	* [https://www.ncbi.nlm.nih.gov/books/NBK557627/ NCBI Bookshelf: Necrosis pathology]
	* [https://www.ncbi.nlm.nih.gov/books/NBK430935/ NCBI Bookshelf: Cell liquefactive necrosis]
	* [https://www.cancer.gov/publications/dictionaries/cancer-terms/def/ischemic-necrosis National Cancer Institute: Ischaemic necrosis definition]

	[[Category:Medicine]]
	[[Category:Pathology]]