pathophysiology of inguinal hernia

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).

39


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

40


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).

41


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

42


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

43


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

44


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

45


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:

46


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

47


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).

48


pathophysiology of inguinal hernia

Health & Medicine