The use of mesh in hernia repair, risk management and the advantages of day surgery

External herniae of the abdominal wall – an introduction to the subject of herniae.

An abdominal wall hernia is a protrusion of the abdominal contents through a defect in the abdominal wall. The term hernia also applies to other sites, including oesophageal hiatus, diaphragmatic and internal abdominal herniae.

The Sac
In most cases the lining of the abdominal wall, the peritoneum, protrudes through a defect and forms a sac, which is described as having a neck, body and fundus. The sac may be permanently prolapsed or only prolapse with increased intra abdominal pressure.

The Contents
The abdominal contents protrude into this sac – either intermittently or permanently. They may consist of omentum or bowel or occasionally other organs.

Extra Peritoneal Fat
At some sites, such as the midline linea alba and femoral canal, extra-peritoneal fat rather than peritoneum protrudes through the defect. There is sometimes a small sac associated.

The Ring
The edge of the defect is called the ring. The changing relationship between the coverings of the hernia, the sac, the contents and the ring are responsible for the symptoms, signs and complications, which can develop with herniae.

The Cause of Herniae
The abdominal wall has well-recognised anatomical sites which are potential weak zones resulting in herniae.

Predisposing Factors are:
A potential weak zone – possibly related to congenital factors

UNDERSTANDING HERNIAS:

1.         The inguinal canal is the most common site by far for the development of a hernia. The 3-layered abdominal wall is modified.  Here as well as at other common sites where herniae are formed, the basic three-layered structure of the abdominal wall is deficient. This with inguinal hernias is associated with the descent of the testis, leaving the posterior wall of the inguinal canal as a potential weak zone.

a)         Indirect herniae occur in infants and children because of a congenital pre-disposition, most commonly in males associated with the descent of the testis and incomplete obliteration of the processes vaginalis.

They are also common in young adults and indeed any age. They descend from the internal ring lateral to the inferior epigastric artery along the cord, or in females the round the ligament.

b)         Direct inguinal hernias do not develop until later in life and almost exclusively in males. The musculature and fascia of the posterior wall undergoes attrition. Commonly the process is bilateral. 

It is not always possible to clinically distinguish between direct and indirect inguinal hernias.

2.         The femoral canal is a potentially weak zone - as the major vessels to the lower limb traverse through the pelvis.

The midline of the abdominal wall – the linea alba, is the most common other site. The single aponeurotic layer is usually thick and strong, but splits can develop causing areas of weakness.

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3.         Epigastric hernias occur at sites of such localised defects.
             Divarication of the recti muscles result in a generalized
             weakness occurring in the midline.

a..                  Umbilical hernia develops at birth through a defect in the umbilicus; a para-umbilical hernia can develop at a later date.  

b.                  Incisional hernias – at the site of a previous operation.

c.                  Recurrent hernias – at the site of a previous hernia repair.

d.                  Rare hernias – often at specific sites – lumbar or spigelian hernias.  

Hernias may result from:  
A.                 Increased intra-abdominal pressure – either acute or chronic. B.                 Any other factor which might further weaken the retaining
             mechanism – muscle, aponeurosis and fascia.  

THE TYPE OF DEFECT
The type of defect through which the hernia protrudes is a major factor in:

A.                 The symptoms or complications which can occur, and

B.                 The method chosen to deal with the sac and the repair of the defect.

A narrow defect with a firm ring is more likely to result in pain and irreducibility, bowel obstruction or strangulation.

A wide bulge in an area of generalized weakness with an ill-defined edge or ring is less likely to be painful and develop complications.

Generally, a hernia which has a well-defined narrow ring is simpler to repair than one where there is a wide bulge with a poorly defined ring. Surgery is preferred for the former type but one can more reasonably delay with the latter.

CONTENTS OF HERNIAS & TERMINOLOGY:
Omentum, small or large bowel or any other viscous or combination may be found in a hernia. Omentum is the most common. It hypertrophies possibly as a result of episodes of sub-acute irreducibility, until it becomes so bulky that it may become irreducible. Adhesions develop between the omentum and the sac. These adhesions are mostly at the fundus and body, but not at the neck. This is typical of indirect inguinal and umbilical herniae.

Reducible Hernia

A reducible hernia is one whose contents return into the abdominal cavity. This is spontaneous when the patient stops straining or lies down. Reduction can also follow manipulation by the patient or physician. Often the patient is best able to reduce the hernia.

The lump may reappear immediately on standing, coughing or straining, or the reappearance may be delayed.

Irreducible Hernia 

An irreducible hernia is one whose contents cannot be returned into the abdominal cavity.

Acute Irreducibility

There is usually acute local pain. There may be central abdominal colicky pain as well. The swelling is tense and tender and lacks a cough impulse. Obstruction and strangulation may soon follow. An elevated temperature, tachycardia and abdominal signs may develop. There may be erythema over the hernia, usually indicating strangulation of contents. This type of hernia needs emergency surgery.