A hernia is a protrusion of a viscus or part of a viscus through an abnormal opening in the walls of its containing cavity.
Composition of a hernia
A hernia consists of three parts – the sac, the coverings of the sac and the contents of the sac.
The sac is a diverticulum of the peritoneum, consisting of mouth, neck, body and fundus. The neck is usually well defined but in some direct inguinal hernias and in many incisional hernias there is no actual neck.
The diameter of the neck is important because strangulation of the bowel is a likely complication when the neck is narrow, as in femoral and paraumbilical hernias.
The body of the sac varies greatly in size and is not necessarily occupied. In cases occurring in infancy and childhood, the sac is gossamer thin. In longstanding cases, the wall of the sac may be comparatively thick.
Coverings are derived from the layers of the abdominal wall through which the sac passes. In longstanding cases, they become atrophied from stretching and so amalgamated that they are indistinguishable from each other.
These can be:
- Omentum = omentocele (synonym: epiplocele);
- I ntestine = enterocele; more commonly small bowel but may be large intestine or appendix;
- A portion of the circumference of the intestine = Richter’shernia;
- S portion of the bladder (or a diverticulum) may constitute part of or be the sole content of a direct inguinal, a sliding inguinal or a femoral hernia;
- Ovary with or without the corresponding fallopian tube;
- A Meckel’s diverticulum = a Littre’s hernia;
- Fluid, as part of ascites or as a residuum thereof.
Classification of hernias
Irrespective of site, a hernia can be classified into five different types.
The hernia either reduces itself when the patient lies down or can be reduced by the patient or the surgeon. The intestine usually gurgles on reduction and the first portion is more difficult to reduce than the last.
Omentum, in contrast, is described as doughy and the last portion is more difficult to reduce than the first. A reducible hernia imparts an expansile impulse on coughing.
In this case, the contents cannot be returned to the abdomen but there is no evidence of other complications. It is usually due to adhesions between the sac and its contents or overcrowding within the sac. Irreducibility without other symptoms is almost diagnostic of an omentocele, especially in femoral and umbilical hernias. Note that any degree of irreducibility predisposes to strangulation.
This is an irreducible hernia containing intestine that is obstructed from without or within, but there is no interference to the blood supply to the bowel. The symptoms (colicky abdominal pain and tenderness over the hernia site) are less severe and the onset more gradual than in strangulated hernias, but more often than not the obstruction culminates in strangulation.
Usually, there is no clear distinction clinically between obstruction and strangulation and the safe course is to assume that strangulation is imminent and treat accordingly.
The term ‘incarceration’ is when the lumen of that portion of the colon occupying a hernial sac is blocked with faeces. In this case, the scybalous contents of the bowel should be capable of being indented with the finger, like putty.
A hernia becomes strangulated when the blood supply of its contents is seriously impaired, rendering the contents ischaemic. Gangrene may occur as early as 5–6 hours after the onset of the first symptoms.
Although inguinal hernia may be 10 times more common than a moral hernia, a femoral hernia is more likely to strangulate because of the narrowness of the neck and its rigid surrounds
Causes of hernias include
■ Intra-abdominal malignancy
Pathophysiology of hernias
The intestine is obstructed and its blood supply impaired. Initially, only the venous return is impeded; the wall of the intestine becomes congested and bright red with the transudation of serous fluid into the sac.
As congestion increases the wall of the intestine becomes purple in colour. The intestinal pressure increases, distending the intestinal loop and impairing venous return further. As venous stasis increases, the arterial supply becomes more and more impaired.
Blood is extravasated under the serosa and is effused into the lumen. The fluid in the sac becomes blood-stained and the shining serosa dull because of fibrinous, sticky exudate. At this stage, the walls of the intestine have lost their tone and become friable. Bacterial transudation occurs secondary to the lowered intestinal viability and the sac fluid becomes infected.
Gangrene appears at the rings of constriction, which become deeply indented and grey in colour. The gangrene then develops in the anti-mesenteric border, the colour varying from black to green depending on the decomposition of blood in the subserosa.
The mesentery involved by the strangulation also becomes gangrenous. If the strangulation is unrelieved, perforation of the wall of the intestine occurs, either at the convexity of the loop or at the seat of constriction. Peritonitis spreads from the sac to the peritoneal cavity.
Clinical features of hernias
Sudden pain, at first situated over the hernia, is followed by generalised abdominal pain, colicky in character and often located mainly at the umbilicus.
Nausea and subsequently vomiting ensue.
The patient may complain of an increase in hernia size.
On examination, he hernia is tense, extremely tender and irreducible, and there is no expansile cough impulse.
Unless the strangulation is relieved by operation, the spasms of pain continue until peristaltic contractions cease with the onset of ischaemia, when paralytic ileus (often the result of peritonitis) and septicaemia develop.
Spontaneous cessation of pain must be viewed with caution, as this may be a sign of perforation.