This is not specific type of necrosis but is a coagulative necrosis occurring due to the loss of blood supply.
This term is used when there necrosis of distal part of limb particularly lower leg and necrosis involving entire thickness of the bowel wall or abdominal viscera.
Types of the gangrenes
Dry gangrene – dead necrotised tissue remains uninfected.
Wet gangrene-necrotic tissue becomes infected.
Gas gangrene – Wet gangrene infected by one of the gas forming Clostridia
Dry gangrene
Gangrene begins in distal part of limb due to ischemia.
Causes-
Atherosclerosis of anteries supplying limb
Thromboangitis obliterans
Raynauds disease
Trauma
Ergot poisoning
Due to ischemia tissues undergoes infarction and line of separation is formed between the necrotic tissue and healthy tissue. At the margins of necrotic tissue, granulation tissue develops.
Morphology:
Grossly the affected part is dry shrunken and dark in colour resembling the mummified foot.
Black colour is due to release of haemoglobin from the haemolysed RBC’s. This is again acted upon by the hydrogen disulfide produced by bacteria which results in the formation of black iron sulphide
Gradually the gangrenous tissue falls from the healthy tissue at the line of separation.
Because of the risk of infection it should be surgically separated.
Wet gangrene:
Wet gangrene typically occurs in
Diabetic foot –High glucose content in the necrosed tissue favours bacterial growth.
Bed sores –In bed ridden patients at the pressure on the sites like sacrum, buttocks and heel
Also in organs like bowel (due to strangulated hernia, volvulus or intusscesception ) lung, mouth, cervix and vulva
Wet gangrene develops more often from the venous blood blockage and also occurs if there is both venous and arterial blood blockage.
Affected part is stuffed with blood which favours rapid growth of putrefactive bacteria
Infection spreads rapidly into the variable tissue adjacent to necrosis.
Even the toxic products formed by the bacteria are absorbed in the circulation causing systemic manifestations like high fever, toxaemia later leading to death
Morphologic features:
Grossly the affected part is black, rotten, and soft and pulpy.
The affected part is dark due to same reason as in dry gangrene
Microscopically the tissue shows caogulative necrosis with extensive areas of haemorrhage.
In the bowel, mucosa is ulcerated and sloughed. Intense acute inflammatory cell infiltrate and thrombosed vessels can be seen.
Line of demarcation between variable and necrosed tissue is absent.
Gas gangrene
It is wet gangrene infected by one of the gas forming Clostridia (Gram positive anaerobic bacteria)
Gas forming Clostridia enters the tissue through a contaminated wound or as a complication of operation on colon which normally contains Clostridia
Clostridia rapidly spreads through tissues especially in muscles and cause extensive necrosis and massive edema
Gas released by the organisms forms bubbles in the tissues giving characteristic crepitations on palpation
Morphology
Gross – the affected part is edematous, swollen and has crepitations on palpation due to accumulation of gas in tissues
Later the tissue becomes dark black and through breach in the skin, gas escapes with foul smelling distinctive odour
Microscopically
Muscle fibres undergo coagulative necrosis with liquefaction
Many Gram positive bacilli can be identified
At the periphery, a zone of leukocytic infiltration, oedema and congestion are found
Capillary and venous thrombosis can be seen
References
J R Bhardwaj, Prabal Deb. Boyd’s Textbook of pathology. 10th edition
