Hernia (in Latin, the rupture of a portion of a structure) is defined as a protrusion of the normal internal abdominal viscera through a weakness or defect in the fascial and muscular layers which normally confine them. The groin region, lying between the lower abdomen and the thigh, represents one of the weakest natural points of the abdominal wall and is the site of most common abdominal wall hernias

1. Pathophysiology of Inguinal Hernia
Hernia (in Latin, the rupture of a portion of a structure) is
defined as a protrusion of the normal internal abdominal viscera
through a weakness or defect in the fascial and muscular layers which
normally confine them. The groin region, lying between the lower
abdomen and the thigh, represents one of the weakest natural points
of the abdominal wall and is the site of most common abdominal wall
hernias (Lawrence et al., 1997).
Incidence:
Inguinal hernias are the most common of all the abdominal
wall hernias and constitute about 80% of cases., with 800,000
inguinal hernia repairs in the USA in 2003 (Rutkow, 2003).
The majority of inguinal hernia occurs in male subjects, with a
male-to-female ratio of 7:1 (Richards et al., 2006).
In adult male 65% of inguinal hernias are indirect and 55% are
right sided. The inguinal hernia is bilateral in 12% cases. If both sides
are explored in infants presenting with one hernia, the incidence of a
patent processus vaginalis on the other side is 60% (Russel et al.,
2004).
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Pathophysiology of Inguinal Hernia

2. Aetiology of inguinal hernia:
1. Patent processus vaginalis:
The prime cause of an indirect inguinal hernia is a patent
processus vaginalis. The processus vaginalis is the direct result of the
migration of the testis from its abdominal location to the scrotum,
which is completed by about 28 weeks of gestation. Normally, the
processus becomes obliterated in the first few months of life. If all or
part of the processus remains patent, the defect can give rise to an
indirect inguinal hernia, a scrotal hydrocele, or an encysted hydrocele
of the cord or hydrocele of the canal of "Nuck" in a female patient.
The congenital etiology of indirect inguinal hernias has resulted in
controversy over the incidence of bilaterality of groin hernias. In a
38-year follow-up of 1,944 patients, investigators found a
contralateral lesion in 15.8 % (Sparkman, 1962).
The extra-abdominal positioning of the testis may be described
as occurring in three steps: a passage is made through the abdominal
wall, which seriously weakens the wall; the testis passes quickly
through the opening into the scrotum; and the passage is reclosed to
restore the integrity of the wall. The first step in the process rarely
causes trouble because the intra abdominal pressure in the fetus is
low when the processus vaginalis is formed. The second step is a
major source of trouble. The testis may be slow in entering the
scrotum, or it may fail to descend at all. In the first instance the testis
may be followed closely by an intestinal loop, before closure can be
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Pathophysiology of Inguinal Hernia

3. accomplished; in the second instance the loop may enter the canal,
which is left open for the descent of the testis that fails to appear on
schedule (Skandalakis, 1994).
Even if the testis passes through the inguinal canal with
dispatch, the third step closure of the internal inguinal ring and
obliteration of the processus vaginalis may be inadequate to restore
the abdominal wall to the strength required for the stresses of later
life in an erect posture. The order of events during closure is:
Step 1: closure of the processus vaginalis at the internal
inguinal ring.
Step 2: closure of the processus just above the testis.
Step 3: atresia of the processus between the constrictors.
The defects that result from failure during individual steps of
the closure may be as follows:
1. Congenital indirect hernia: failure of closure of the internal
ring and all subsequent steps.
2. Acquired indirect hernia: failure of closure of the internal
ring, with successful completion of the second and third steps.
3. Infantile hydrocele: inguinal ring closed, the second and
third steps are not completed.
4. Cystic hydrocele: only the third step is not completed
(Skandalakis, 1994).
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Pathophysiology of Inguinal Hernia

4. 2. Weakness of the Shutter Mechanisms:
Coughing, straining, and lifting of heavy weights and other
normal daily activities generates extremely high intra-abdominal
pressures, yet the natural weakness of the groin, such as the internal
inguinal ring and transversalis fascia, maintain their integrity in the
overwhelming majority of individuals and even in those with an
internal inguinal ring and a patent processus vaginalis The accepted
explanation for this is the physiologic "shutter mechanism", which is
activated when the abdominal muscles contract and cause the intra-
abdominal pressure to increase when performing these functions. As
the internal oblique and transversus abdominis muscles contract, their
lower fibers forming the myoaponeurotic roof of the inguinal canal,
the "conjoined tendon" that arches over the spermatic cord also
sharply contracts and as the fibers shorten, the arch straightens out
and descends to come to lie close to or on the inguinal ligament and
so covers and protects the fascia transversalis. The shutter also passes
down in front of the internal ring and counteracts the pressure on the
ring from inside the abdomen. Contraction of the transversus
abdominis muscle also pulls up and tenses the crurae of the internal
ring, which are made up of thickened bands of the iliopubic tract and
fascia transversalis, causing the ring to close like a sphincter snugly
around the cord.
At the same time the external oblique muscle contracts, its
aponeurosis, which forms the anterior wall of the inguinal canal
becomes tense and presses on the internal inguinal ring and on the
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Pathophysiology of Inguinal Hernia

5. weak posterior wall of the inguinal canal and so reinforces them by
counter pressure against the intra-abdominal forces that push
outward. The inguinal ligament is also pulled upward by the same
contraction to become convex cranially. The act of contraction' of the
abdominal muscles in coughing or straining, which tends to blow out
the internal ring and the fascia transversalis automatically and at the
exact same moment, brings into play mechanisms that resist
this damage (Abrahamson, 1998).
3. Raised intra-abdominal pressure:
The cause of hernia was mechanical disparity between intra-
abdominal pressure and the resistance of the abdominal musculature.
If the first increased over the second, hernia emerged through a weak
point of the abdominal wall. However, recent work suggests that
these conditions do not cause groin hernias on their own but may be
additional facilitating factors acting on the basic etiology to bring on
a hernia (Abrahamson, 1998).
When the intra-abdominal pressure, is actively raised, as in
coughing, straining, or lifting, the counter mechanisms are
automatically activated and together with the transversalis fascia, are
usually sufficiently efficient to resist the increased pressure, and a
hernia does not appear; however, when the intra-abdominal pressure
rises passively and the abdominal muscles are relaxed, these
mechanisms are not activated, so that the fascia transversalis is left
on its own to withstand the increased intra-abdominal pressure. If a
patent processus vaginalis is present, or if the fascia transversalis is
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Pathophysiology of Inguinal Hernia

6. not sufficiently strong or becomes attenuated by prolonged pressure
and stretching, it gives way, and an indirect or direct hernia appears.
This situation is seen in pregnancy, where a groin hernia may appear
or the first time and may even "disappear" after the delivery. This is
usually an indirect hernia that appears in a patent processus vaginalis
that has been present as a latent hernia only, but direct and femoral
hernias also appear during pregnancy. A similar mechanism produces
groin hernias, and often an umbilical hernia as well in cases of
chronic ascites caused by liver cirrhosis (Belghiti et al., 1992).
4- Loss of the integrity of fascia transversalis:
The fascia transversalis, like other fascial tissue, derives its
strength from collagen fibers that are continually being produced and
reabsorbed. A disturbance of this balance results in attenuation of the
fascia. Congenital defects, such as occur in Marfan, Ehlers-Danlos
and Hunter-Hurler syndromes, can predispose to hernia formation. It
appears that certain lifestyles can lead to defective collagen
production, including the now rare condition in which a patient
ingests large quantities of foods that contain elaminopropionitrile.
This substance prevents covalent cross-linking between and within
forming collagen molecules, so that collagen is produced that is
reduced in tensile strength (Abrahamson, 1994).
5. Cigarette Smoking:
An association between cigarette smoking and groin hernias
has also been demonstrated. Levels of circulating serum elastolytic
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Pathophysiology of Inguinal Hernia

7. activity have been shown to be significantly greater in patients who
smoke (Read, 1992).
It was found that substances in cigarette smoke inactivate
antiproteases in lung tissue and so upset the protease/antiprotease
system, which is responsible for the integrity of the lung tissue
leading to its destruction and emphysema. The free, unbound and
active protease and elastase compounds are also found in the serum
of smokers, apparently discharged by the increased number of
circulating white blood cells in the blood and lungs of smokers.
These circulating unopposed enzymes upset the protease antiprotease
system in the blood and bring about destruction of elastin and
collagen of the rectus sheath and fascia transversalis and so cause
their attenuation and predispose to herniation in cigarette smokers.
The level of circulating serum elastolytic and protease substances is
higher in the blood of patients with hernias than in controls, in those
with direct compared with indirect hernias, and still higher in those
with bilateral direct inguinal hernias (Read, 1998).
Smoking, the most common cause of pulmonary emphysema,
evokes a neutrophil-macrophage response.
Priming of these white cells and their 5 to 10 fold concentration
in the lungs, with release of elastase and collagenase, destroys the
parenchyma. Further, oxidant, produced from combustion of tobacco
damage antiprotease defenses. To explain the systemic effect on
connective tissue, in particular those observed in the groin, it was
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Pathophysiology of Inguinal Hernia

8. investigated that the chronic inflammatory response in the lungs
affects the circulating blood. Uninhibited proteolytic activity, large
numbers of activated neutrophils and macrophages, along with
products of tobacco combustion, caused peripheral collagenolysis
and inhibited repair. The process, metastatic emphysema, is
analogous to the distant damage seen in the lungs and skin of patients
with acute pancreatitis or visceral ischemia (Read, 2002).
6. Trauma: Spontaneous or iatrogenic:
It is remarkable how strong the abdominal wall is. It takes
massive trauma to cause inguinal herniation. Aponeurosis are then
detached from their insertions into the pubis. A similar result can
follow fractures or osteotomies. Symphysiotomies, especially for
prostatic surgery, if not properly repaired, cause distraction of the
rectus tendon insertion and suprapubic or parapubic herniation,
sometimes diagnosed as primary direct inguinal defect. Previous
appendectomy may be followed by right inguinal herniation.
However, the classic McBurney incision rarely produces such sequel.
Apparently, the more cosmetic unilateral Pfannenstiel approach has
been incriminated because of damage to the iliohypogastric nerve
(Read, 2002).
7. General factors:
The ability of the abdominal wall in the groin to withstand the
forces in favor of herniation may be reduced by:
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Pathophysiology of Inguinal Hernia

9. The weakening of the muscles and fascia with advancing age,
lack of physical exercise, adiposity, multiple pregnancies, and loss of
weight and body fitness as may occur after illness, operation, or
prolonged bed rest.
Certain "cosmetic" operative incisions, such as very low and
unduly long transverse abdominal incisions for gynecologic or
urologic procedures or "cosmetic" appendectomy incisions, may be
followed by the appearance of a groin hernia caused by cutting into
the myoaponeurotic arch of the lower fibers of the internal oblique
and transversus abdominis muscles and/or cutting across the motor or
sensory nerves of the groin, causing atrophy of the muscles.
The incidence of groin hernia is the same in sedentary workers
as in heavy manual laborers, indicating that strenuous physical
activity alone does not cause hernias; however, it does bring about a
rise in the intra-abdominal pressure and so may cause an existing
small unnoticed groin hernia to expand and become more obvious. It
may also be the final factor bringing on a hernia in these already
predisposed to herniation by other, more basic causes (Abrahamson,
1998).
The cause of hernia is probably multifactorial. In case of
indirect hernia a preformed sac of processus vaginalis is probably
present but bowel is prevented from entering by efficient muscular
action. In direct hernia, there is no preformed sac, in fact, the
protective mechanisms fail. The weakened transversalis fascia on its
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Pathophysiology of Inguinal Hernia

10. own can not withstand the repeatedly raised intra abdominal pressure
and stretches, ballooning out in front of the advancing bowel, or
simply tears and allows the peritoneum covered bowel to pass
through it. The reason that inguinal hernias are more common in
elderly may be linked to the findings of Rodrigues who in 1990
reported a decrease in oxytalan fibers and increase in amorphous
substances of the elastic fibers as a function of age, which may be
responsible for alteration in the resistance of the transversalis fascia
(Abrahamson, 1997).
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Pathophysiology of Inguinal Hernia