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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.
*Sloughing means necrosis or death of soft tissue and the dead area is called
slough.
*Sequestration means 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).
*Gangrene means local death and putrefaction of a tissue while being
attached to the living body.
Etiology:
1-Direct injury of tissue (1ry gangrene)
a-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).
b-Physical causes as burns or frostbite.
c-Chemical causes like acids, alkalis, caustic substances, or even natural
body fluids in aberrant location (subcutaneous urine in case of ruptured
urethra).
d-Infectious cause like bacterial infection with production of toxins.
2-Indirect causes (2ry gangrene)
a-Nervous causes like atrophy after neurectomies.
b-Vascular causes like arteriosclerosis, arterial spasm (by drugs as ergot), or
embolism; or venous thrombosis or phlibitis. Mechanical prolonged closure of
blood supply by tourniquet, tight bandage, pressure of displaced bone
fragment, or strangulation.
c-Bacterial toxins.
Classification:
1- Primary and secondary gangrene
a-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.
b-Secondary gangrene
It is the result of tissue death due to disturbance in blood supply, followed by
invasion by putrefactive bacteria.
2-Dry and moist gangrene
a-Dry gangrene (death mummification)
This type of gangrene occurs in tissues that have adequate venous drainage.
The usual cause is chronic arterial obstruction as arterial sclerosis or
calcification of the terminal end of the arteries (sit-fast). Affected tissue
becomes hard, dry, shrunken, and dark brown to black, but no putrefaction
can be observed.
b-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.