(Posted:25-Jun-2015)

Gangrene is a necrosis of tissue with superadded putrefaction. There are three types of gangrene: Dry gangrene. Moist gangrene. Gas gangrene. Dry gangrene: Dry gangrene occurs due to lack of arterial blood supply,which may occure in: 1) Changes in arterial wall e.g:atherosclerosis,arteriosclerosis. 2)Spasm of artery e.g:Raynaud's disease,ergot poisoning. 3)Obstruction of lumen of the artery.e.g:thrombosis,embolism. 4)Pressure from outside by tumour,tight plaster. Pathogenesis and pathology:Dry gangrene occurs due to lack of arterial blood supply in the extremities,particularly lower extremity.Usually start to the great toe.The area is cold,dry,shriveled,mummified,black due to iron sulphide and foul smelling.Iron is derived from haemolysed red blood cells and hydrogen sulphide is produced due to putrefaction by invaded saprophytes.The area of gangrene may gradually extend proximally. Moist gangren: Pathogenesis and pathology:Moist gangrene develops due to obstruction of both arterial supply and venous drainage,particularly in moist areas.The gangrenous part is moist,blackish and offensive in smell.There is no line of demarcation. Sites:Intestine,mouth,bed sores,vulva,scrotum,anterior abdominal wall. Gas gangrene: Gas gangrene is caused by anaerobic clostridium perfringes in most cases and rarely by C.novyi and C.septicum.These pathogens are virulent due to their powerfull exotoxins and enzymes.The main sources of clostridia in animal and human excreta. Pathogenesis: 1) Nature of wound predisposes to clostridial infection and germination of spores.Reduced oxygen tension is essential for germination of spores. 2)Necrosis of muscle fibres occures by the exotoxins.Certain clostridia ferments carbohydrates with production of lactic acid,carbon dioxide and hydrogen. 3)Putrefaction is caused by the proteolytic clostridia.They breakdown proteins liberating nitrogenous base,ammonia and nitrogen. 4)Necrosis proceeds by the toxin and ischaemia due to pressure on blood vessels by gas and exudate. 5)Rapid spread of infection occures due to breakdown of tissue barriers by the hyaluronidase and collagenase produced by the bacteria. Morphology: Gross:The area is swollen.Muscle appear brick red and then black and become soft and friable.Discharge is foul smelling and serosanguinous. Microscopic: Marked oedema,gas.Necrosis of muscle fibres.Inflammatory cells are a few.Thrombosis may be in vessels. General effect may be: Toxaemia and septicaemia.