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mon, October 17, 2016
DR.ABDIAZIZ ABDI MOHAMED
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Contents
Definition
 Mechanism
 Causes
 Gross appearance and types of
gangrene

 Wet
 Dry
 Gas
Microscopic appearance
Effect of gangrene on body systems
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Definition
 Gangrene refers to an area of
necrosis which is invaded by
saprophytic and/or putrefactive
bacteria.
 It is the invasion and putrefaction of
necrotic tissue by saprophytic
bacteria.
 Necrosis occurs first and is then
followed by infection..
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Mechanism
 Initially,
the tissues undergo
coagulative necrosis;
subsequently, the coagulated
tissues are invaded by
saprophytic and/or
putrefactive bacteria which
attract neutrophils to the
area.
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Mechanism (cont)
 The
liquefactive action of the
bacteria and the lysosomal
enzymes released by the
invading neutrophils modify the
coagulated tissue.
 It is, in reality, a combination of
coagulative and liquefactive
necrosis.
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Mechanism (cont)
 If
the coagulative pattern is
dominant, the process is
called dry gangrene.
 However,
if the liquefactive
pattern is more pronounced, it
is named as wet gangrene.
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Causes of gangrene
 Caused
by the same factors that
cause necrosis, but in gangrene is
invaded by saprophytic bacteria.
 Area of occurrence:
 It is occurs in tissue that more
exposed to saprophytic bacterial
contamination e.g. skin, extremities,
intestine, lung and mammary
glands.
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Causes of gangrene (cont)
 Gangrene
occurs in skin, tail,
ear and extremities in case of
closure of blood supply due to
the following:
 1- ergot toxins (fungal toxins lead
to contraction of small muscle in
the arteries).
 2- compressed bandages.
 3- sever cold (freezing).
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Causes of gangrene (cont)
○ In intestine gangrene occur due in
cases of torsion, and volvulus.
 In lung in aspiration pneumonia.
 In mammary gland, in some
acute bacterial inflammations
(staph.aureus, E.coli, etc.)
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Gross appearance and types
of gangrene
 Gangrene
can be classified
grossly to the following types:
 1- Moist gangrene
 2- Dry gangrene
 3- Gas gangrene
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1- Moist gangrene
 Causes
:
 Twisted intestine
(gangrenous enteritis)
 Lung due to aspiration
(gangrenous pneumonia)
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Moist gangrene (cont)
 Gross:
 Swollen, edematous, soft,
dark in color friable and easy to
rupture with air bubbles and
putrefactive smell and
indistinctive demarcation line
(due to progressive gangrene).
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Moist gangrene
Loop of discolored
necrotic small
intestine in a dog.
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Lung from a dog. Stomach
contents were aspirated
during surgery.
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2- Dry gangrene
 Causes:
 Seen in extremities due to
vascular compromise or
ischemia (tail, ears, toes);
ergot.
 In sever cold (freezing).
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Dry gangrene (cont)
 Gross:
 Tissue is shrunken, wrinkled,
often firm.
 Can be pale or darker than
normal.
 Marginal hyperemia- red line
of inflammatory demarcation.
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Dry gangrene
Ear tips from a bovine.
One can barely see a red
line of demarcation on the
viable border of the ear.
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Ear of a pig.
The red line of demarcation
is much more obvious here.
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3- Gas gangrene
 Gas
gangrene is the term
commonly used when necrotic
tissue is invaded by bacteria
that produce large amounts of
gas from constituents of the
dead tissue.
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Gas gangrene (cont)
Causes:
 Several species of genus
Clostridium are capable of
producing gas gangrene.
 e.g. Clostridium septicum and
Clostridium chauvoei are able to
kill animal tissue and then continue
to multiply in it, producing large
amounts of gas.
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Microscopic appearance
of gangrene

In general gangrene, characterized by
severe coagulative necrosis and
presence of large numbers of
saprophytic bacteria which appears as
blue bacilli (H&E satin).

In moist gangrene, edematous fluids
appears as amorphous, homogenous
material pink in color (H&E stain)
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Microscopic appearance of
gangrene (cont)
 Un
stained spaces with
irregular margins (indicate air
bubbles).
 Demarcation
line (large
numbers of inflammatory cells
(neutrophils) in addition to
bloods vessels.
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Effect of gangrene on the
body
 In
general gangrene is danger
condition which can lead to death
(absorption of toxic products of the
organisms).
 Moist
gangrene spread rapidly
(presence of blood supply, and high
body temperature which enhance
the multiplication of bacteria).
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THE
END
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