Gangrene 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
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