◊ Necrosis & Gangrene ◊

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NECROSIS AND GANGRENE

Definition: -

Necrosis is a collective term means localized death of cells or tissue within the body as a result of loss of nutrition, injury, disease, or other pathologic state.

Sloughing means necrosis or death of soft tissue that is followed by casting off, and the dead area is called slough.

Sequestration means that a fragment of dead bone separated from healthy bone as a result of injury or disease or it is necrosis of bone and the dead fragment is called sequestrum.

Necrobiosis means aseptic necrosis of tissue as a result of occlusion of its blood supply (infarction).

Cells that die due to necrosis do not usually send the same chemical signals to the immune system that cells undergoing apoptosis (natural death of cells) do. This prevents nearby phagocytes from locating and engulfing the dead cells, leading to a build-up of dead tissue and cell debris at or near the site of the cell death. For this reason, it is often necessary to remove necrotic tissue surgically, a process known as debridement. In addition necrosis can release harmful chemicals into the surrounding tissue. In particular, cells contain small organelles called lysosomes, which are capable of digesting cellular material. Damage to the lysosome membrane can trigger release of the contained enzymes, destroying other parts of the cell. Worse, when these enzymes are released from the non-dead cell, they can trigger a chain reaction of further cell death. If a sufficient amount of contiguous tissue necrotizes, it is termed gangrene. Proper care and treatment of wounds or animal bites plays a key role in preventing this type of widespread necrosis. During a surgical biopsy, this necrosis chain-reaction is halted by fixation or freezing

Necrosis typically begins with cell swelling, chromatin digestion, and disruption of the plasma membrane and organelle membranes. Late necrosis is characterized by extensive DNA hydrolysis, vacuolation of the endoplasmic reticulum, organelle breakdown, and cell lysis. The release of intracellular content after plasma membrane rupture is the cause of inflammation in necrosis.

Gangrene means death and decay of body tissue or local death and putrefaction of a tissue while being attached to the living body usually caused by impaired or absent blood supply. Gangrene can occur as a result of arterial or serious venous damage. The effect of gangrene can be disastrous, leading to loss of limbs. It can also cause the products of tissue breakdown to enter the bloodstream causing blood poisoning and threatening life.

Causes of necrosis: -

Cellular necrosis can be induced by a number of external sources, including injury, infection, cancer, infarction, poisons, and inflammation. For example, an infarction (blockage of blood flow to muscular tissue) causes necrosis of muscle tissue due to lack of oxygen to the affected cell, such as occurs in a myocardial infarction. Certain spider and snake venoms can cause necrosis of the tissue near the bite wound, as can a group A streptococcus infection (one of the "flesh-eating" bacteria).

Treatment: -

Treatment of necrosis typically involves two distinct processes. Usually, the underlying cause of the necrosis must be treated before the dead tissue itself can be dealt with. For example, a snake or spider bite victim will receive anti-venom to halt the spread of the toxins, while an infected patient will receive antibiotics.

Even after the initial cause of the necrosis has been halted, the necrotic tissue will remain in the body. The body's immune response to apoptosis, the automatic breaking down and recycling of the cell material, is not triggered by necrotic cell death.

The standard therapy of necrosis (wounds, bedsores, burns, etc.) is surgical removal of necrotic tissue. Depending on the severity of the necrosis, this may range from removal of small patches of skin, to complete amputation of affected limbs or organs. Chemical removal, via an enzymatic debridement agent, is another option. In selected cases, special maggot therapy has been utilized with good results.

Causes of gangrene: -

I-DIRECT INJURY OF THE TISSUE (primary gangrene)

1-Mechanical or traumatic injury to tissue, crushing of blood supply, or prolonged pressure (by harness as sit fast or against bony prominence as bed sore)

2-Physical causes as burns or frostbite

3-Chemical causes like acids, alkalis, caustic substances, or even natural body fluids in aberrant location (subcutaneous urine in case of ruptured urethra)

4-Infectious cause like bacterial infection with production of toxins

II-INDIRECT CAUSES (secondary gangrene)

1-Vascular causes like arteriosclerosis, arterial spasm (by drugs as ergot), or embolism; or venous thrombosis or phlebitis. Mechanical prolonged closure of blood supply by tourniquet, tight bandage, pressure of displaced bone fragment, or strangulation

2-Bacterial toxins

Classification

I-PRIMARY or SECONDARY GANGRENE

1-Primary Gangrene

It is the result of invasion of the tissue by gangrene-producing organism like black quarter in sheep and cattle, malignant edema in horse, and gangrenous udder due to staph and strept.

2-Secondary Gangrene

It is the result of tissue death due to disturbance in blood supply, followed by invasion by putrefactive bacteria.

II-DRY or MOIST GANGRENE

1-Dry Gangrene (death mummification)

This type of gangrene occurs in tissues that have reduction of blood flow through the arteries with adequate venous drainage. The usual cause is chronic arterial obstruction as arterial sclerosis or calcification of the terminal end of the arteries (sit-fast), accordingly it appears gradually and progresses slowly. Affected tissue becomes cold, hard, dry, shrunken, and dark brown to black, and eventually sloughs off but no putrefaction can be observed as the affected part does not become infected.

2-Moist gangrene

This type is observed in tissues that are rich in fluid and have inadequate venous drainage. It usually occurs as a result of venous obstruction followed by sudden arterial obstruction, and the affected tissue become swollen, disintegrated and liquefied by the action of putrefactive bacteria with production of blood stained foetid fluid and toxins.

Wet or moist gangrene also develops as a complication of an untreated infected wound. Swelling resulting from the bacterial infection causes a sudden cessation of blood flow that facilitates invasion of the muscles by the bacteria and multiplication of the bacteria because disease-fighting cells (white blood cells) cannot reach the affected part.

Gas gangrene is a type of wet gangrene caused by the bacteria known as Clostridia. Clostridia are a type of infection-causing bacteria that grow only in the absence of oxygen. As Clostridia grow, they produce poisonous toxins and gas; therefore, the condition is called gas gangrene.

Signs of death of tissues

1-Loss of arterial pulsation

2-Loss of sensation as a result of death of nerve endings

3-Pain due to irritation of the healthy nerve endings

4-Loss of function

5-Loss of heat (cold in palpation)

6-Changes in color

Symptoms of gangrene

I-LOCAL SYMPTOMS

1-Period of Death

In case of dry gangrene, the dead part becomes hard, dry, shrunken, dimensioned in volume (adequate venous drainage), dark color, and the hair become dry and erected.

In case of moist gangrene, the volume of the affected tissue increases (as a result of inadequate tissue drainage), the color changed into green or black color, epithelium can be scraped from the skin, the affected organ becomes cold, and offensive odor discharge comes out from the affected tissue.

2-Period of Separation of the Slough

An inflammatory line of demarcation separates the affected tissue from the healthy one. The dead area cast off indicating that toxemia wasn’t sufficient to kill the animal. During this period, many complications can occur, like secondary hemorrhage as a result of sloughing of blood vessels, septic arthritis as a result of opening of a joint, or synovitis as a result of opening of tendon sheath.

3-Period of Cicatrisation

Once the slough has separated, healing ensues, except the parts of hard necrotic tissues like cartilage or bone that separated slowly.

II-CONSTITUTIONAL or GENERAL SYMPTOMS

These symptoms ensue mostly as a result of absorption of toxins, and these symptoms include fever, rapid pulsation, and harried respiration, loss of appetite, exhaustion, and death.

Diagnosis: -

1-History

2-Symptoms

3-Clinical examination

Prognosis: -

Prognosis depends up on the nature of the lesion. When toxemia is severe, the case is dangerous as in moist gangrene and death may occur within few days as with gangrenous mastitis or even within hours as with strangulating intestinal obstruction.

Treatment:

1-Local Treatment

It must be directed toward prevention of extension of gangrene and stimulate fast separation of the slough.

1-Removal of the cause

2-Excision of the mummified part in case of dry gangrene

3-Application of irritants at the periphery of the dead tissue to enhance separation

4-Application of warm antiseptics dressing if intense inflammation is present in the vicinity

5-In case of moist gangrene, surgical debridement (removal of dead tissue), scarification of the lesion, or even puncture with hot iron must be performed (permitting the escape of toxic liquids, and to irrigate the tissue with antiseptic solution)

6-Stimulation of granulation and healing

7-If the case is hopeless, amputation of the affected appendages or organ can be performed to save the life of the animal

2-Treatment of Constitutional Symptom

1-Administration of easily digestible food

2-Administration of systemic antibiotic

3-Administration of vitamins, minerals, tonics and stimulants

4-Administration of analgesics for controlling the pain

Regarding gas gangrene, the condition needs to be treated aggressively because of the threat of the infection rapidly spreading via the bloodstream and damaging vital organs. The wound requires immediate debridement and antibiotics are administered to the affected animal.