Posted by DAM on February 2, 2012 in CIRCULATORY DISTURBANCES | Short Link
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Definition: it is necrosis of tissue with super-added putrifaciton.

Gangrene may be:

  1. Primary.
  2. Secondary.


    The difference lies in the cause of the tissue necrosis.

  • Primary gangrene: is brought about by infection with pathologic bacteria which both kill the tissue by secreting potent exotoxins and then invade and digest the dead tissue e.g. gas gangrene.
  • Secondary gangrene: in which necrosis is due to some other cause usually loss of blood supply from vascular obstruction or tissue laceration and saprophytic bacteria then digest these dead tissues e.g. dry and moist gangrene.

Types of gangrene: There are three types:

I- Dry gangrene:

Usually occurs in the limbs which are exposed to dryness by evaporation of the tissue fluid. Lower limbs are more commonly affected than upper limbs, starting from the big toe which is the farthest point of circulation.



1 – The Cause of necrosis is cut of blood supply in tissues with poor collateral circulation due to:


a- Atheroma or arteriosclerosis is the commonest cause especially in old age and it is called senile gangrene. It leads to inadequate collateral circulation followed by thrombosis in a main artery with cut of blood supply.

b- Embolism.

c- Spasmodic contraction of arteries as occurs in Raynaud’s disease.

  1. Causes of putrefaction: are usually putrefactive micro-organisms which ingest and digest the dead tissues.



  1. Early manifestations of gangrene, the affected limb, cold, pale, with loss of sensation and loss of function.
  2. The process of gangrene starts in the big toe and gradually ascends up the limb until there is an adequate blood supply where it stops.
  3. The affected part becomes dry, shrunken and mummified.
  4. A series of colors appear in the form of red, green, and then black depending on the increasing amount of iron sulphate (due to action of hydrogen disulphide produced by bacteria on the hemoglobin of the red blood cells).
  5. Putrefaction is minimal and spread of gangrene is slow due to lack of fluids. The toxemia is minimal and that is why the general condition of the patient is good.


  1. The living tissue just near the gangrenous part, become irritated forming thin line of granulation tissue which appears red in color and is called “line of demarcation” later on it is transformed into fibrous part and so it will be called “line of separation”. The separated gangrenous part is called “slough” and the remaining part is called “stump” which appears conical in shape because the blood supply of the skin and subcutaneous tissue is less abundant than that of the muscle and bones.



II- Moist or wet gangrene: it is very serious and usually fatal. It usually develops in parts where there is excess tissue fluids as occurs in the following sites:

1- Moist gangrene of the limbs: gangrene of limbs may be of the moist type in the following conditions:

a- Diabetic patients: where the arteries and collaterals are already narrowed due to accompanying arteriosclerosis. In addition, the excess sugar in tissues favors bacterial infection inducing thrombosis in arteries and veins to occur. The limb becomes edematous and thus the gangrene is going to occur in the moist type. Diabetic gangrene occurs in younger people.

b- In old persons: if there is edema of lower limbs, due to any cause, and gangrene is going to occur, it will be of the moist type due to presence of excess edema fluid.

c- Following severe crushing injury of the limb, a thrombus will occur in both arteries and veins. Thrombosis in veins leads to edema of lower limbs and thrombosis in arteries lead to cut of blood supply followed by gangrene which in this condition will be of the moist type due to edema.

Internal organs such as:

a- Intestines: Necrosis of a loop of the intestine occurs due to cut of blood supply as occurs in strangulated hernia, thrombosis or embolism of one of the mesenteric arteries. This is followed by invasion of this dead segment by the putrefactive organisms, present normally in the lumen of the intestine as B. Lactis aerogenes. The color of this part rapidly turns black due to iron sulphide with very offensive odor. The general condition of patient is very bad due to marked toxemia and the manifestations of acute intestinal obstruction.

b- Lungs: Especially if there is severe infection such as bronchopneumonia, lung abscess, in a patient with marked lowering of resistance, senility and diabetes.

c- Appendix: In acute suppurative appendicitis if thrombosis occurs in appendicular artery leading to cut of blood supply.

Moist gangrene of the skin of the back (known as “bed sores”: It is a common complication in prolonged recumbancy due to paralysis or fracture. It occurs over the sacrum and buttocks due to pressure opposite boney prominences leading to cut of blood supply in the arteries of the skin. Important predisposing factors as old age, long standing illness with malnutrition and deficiency of proteins. The dead tissues are cast off, lead to a sore which exposes the underlying bone.


Pathogenesis of wet gangrene:

  1. The affected part is swollen, edematous and there may be ulcerated and shows blebs containing bubbles of gas.
  1. The series of colors usually appears very rapidly.
    1. Putrefaction is maximal with very bad odor and marked acute toxemia which is the usual cause of death.
    2. The line of demarcation will not appear because the process of gangrene is rapid.


Ill- Gas gangrene: It is a rare disease usually affecting the muscle in neglected wound particularly those of wars, may follow surgical operations when there are septic conditions. The commonest cause are spores of Clostridium which are introduced into deep wounds germinate rapidly under anaerobic conditions, proliferate and produce toxins which cause extensive necrosis of muscles and at the same time produce putrefaction in dead muscles which acquires a green or black color. Toxemia is severe and fatal.

Cancrum oris: It is caused by bacteria e.g. Borrelia vincenti and fusiform bacteria (normal flora of the mouth) which cause necrosis of the gum and then spread to the cheek then the dead tissues undergo putrefaction. Deficient intake of vitamin B complex predisposes to the condition. Usually this condition occurs in poorly nourished children.



Difference between dry and moist gangrene


Point of comparison 



Mode of onset 



Site of gangrene 


Limbs and internal organs 

Site of occlusion 


Artery and veins 

Cause of necrosis 

Tissue anoxia 

Tissue anoxia or toxins 

Tissue fluids 



Size of affected part 



Line of demarcation 

Well formed

Poorly formed 





Slow, may end in self-separation 

Rapid and fatal 




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