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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 wall. The term hernia also applies to other sites, including oesophageal hiatus (hiatus hernia), 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.

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 contens 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. A potential weak zone - possibly related to congenital factors
B. Increased intra-abdominal pressure - either acute or chronic
C. Any other factor which might further weaken the retaining mechanism - muscle, aponeurosis and fascia

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

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 processus vaginalis.

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

The femoral canal is a potentially weak zone.

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.

Such localised defects result in the formation of epigastric hernias.

A generalised weakness results in the development of divarication of the rectus muscle.

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

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 generalised 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.

Omentum
Omentum, small or large bowel or any other viscus 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 is 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 herniae 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 spontaneously or by manipulation by the patient or doctor.

Incarcerated hernia - imprisoned - implies that the hernia is trapped and can not get out or be reduced.
Can be applied to all different hernia sites.

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.

Chronic Irreducibility
These are not usually acutely/ severely painful or tender. Abdominal pain is not a feature. Emergency surgery is not necessary, although a chronically irreducible hernia may still become strangulated.

Herniae are a very common problem and while they can cause abdominal pain, the possibility of a co-existent lesion in the bowel, such as a carcinoma of a colon, particularly in the elderly, must always be borne in mind.

Practical Management of an Acutely Painful or Strangulated Hernia
In early cases, gentle manipulation or taxis to reduce the hernia may be attempted.

When analgesics are given the hernia sometimes reduces spontaneously because the ring and surrounding muscles are relaxed. Similarly in the theatre the hernia reduces on induction of the anaesthetic.

This suggests that the process is not so advanced and at operation the contents will be found to be viable.

At operation the contents should be controlled so that they do not slip back and can be inspected to determine whether resection is necessary. Should the contents slip back before inspection, a laparotomy may be necessary. In addition the infected or gangrenous contents can contaminate the abdominal cavity.

It is sometimes difficult to be sure which layer is the sac during dissection. The blood-stained fluid within the sac can look like bowel. The fluid layer reduces the risk of damage to the bowel as the sac is opened. Once the sac is opened the contents can be inspected and grasped gently while the ring is divided. The ring can be tight and there is a danger of damage to the bowel. This must be avoided. Then the contents are delivered further into the wound, and in the case of bowel, both the proximal and the distal limb as well as the site of constriction must be inspected to ensure they are viable.

Obstructed, Incarcerated and Strangulated
These clinical terms are used to describe events associated with an acutely tender irreducible hernia. These terms suggest the blood supply is occluded and the delay will result in ischaemia, necrosis and gangrene.

While obstruction and incarceration suggest the sequence is less advanced than strangulation, clinical differentiation is difficult and may demand surgical exploration.

Any acutely painful irreducible hernia should be considered strangulated and considered for urgent surgery.
At least urgent referral to a surgeon is required.

The sequence of events are best related to the findings at operation.

Pathology
Initially the omentum or loop or bowel with its mesentery are trapped at the tight ring (imprisoned or incarcerated). Lymphatic obstruction results in an oedematous appearance and serous fluid is found in the sac.

With venous obstruction, bruising and ecchymoses develop and extend. The fluid in the sac becomes increasingly blood-stained.

With persistent complete arterial blockage, the omentum or the loop of bowel, superimposed on previous widespread ecchymoses, becomes plum-coloured and then black because of anoxia. The fluid becomes heavily blood-stained and foul smelling, with bacterial invasion.

The site at which the contents are constricted is often more severely affected - "constriction rings: are formed. When the obstruction is released at a later stage no blood oozes from the surface of the bowel or at the site of the constriction rings and the normal colour does not return. Arterial pulsation and peristalsis in the bowel do not reappear.

In Summary
The terms obstructed or incarcerated are not very precise terms. It implies an irreduceable hernia which possibly has bowel contents. This type of hernia may go on to strangulation. It implies that the process may proceed to strangulation, but these changes have not yet occurred. Rapid progress to overt strangulation with necrosis followed by perforation and peritonitis may occur.

Should an acutely irreducible hernia reduce spontaneously and immediate surgery not be arranged, a close clinical watch must be instituted for irreversible damage may nevertheless occurred.

The symptoms and signs of the development of strangulation can be masked particularly in :
A. Infants
B. The elderly or frail
C. Those who have not been given a narcotic agent for the relief of pain and
D. The obese

A close clinical watch is instituted if uncertain. Surgical action is preferred rather than excessive delay.