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Hernia

Definition:

A hernia is a ‘protrusion of a viscus or other structure beyond the normal coverings of the cavity in which it is contained or between two adjacent cavities, such as the abdomen and the thorax, or into a subcompartment of a cavity’
The first category is commonly called external and the second and third are internal
The most frequent hernias are external ones of the abdominal wall in the:

Inguinal
Femoral
Umbilical, regions

Classification

Hernias are best classified as congenital or acquired

Congenital:

There is a pre-formed sac which occurs as a consequence of the ordered or disordered process of intra-uterine development
The patent processus vaginalis is a good example

Acquired – are 2 types:

Primary hernias – occur at natural weak points
Secondary hernias – develop at sites of surgical or other injury to the wall which normally constrains the contents of a body cavity (usually the abdomen)

Aetiology:

The 2 main factors predisposing to hernia are increased intracavity pressure and a weakened abdominal wall. Using the abdomen as an example:

Increased intra-abdominal pressure:

Heavy lifting
Persistent cough (e.g. COAD)
Straining to pass urine (e.g. BPH)
Straining to pass faeces (>15% of men with large bowel cancer present with an inguinal hernia)
Abdominal distension (faeces, fat, flatus, fluid, foetus)

Weakened abdominal wall:

Abnormal collagen metabolism
Advancing age
Malnutrition
Damage to, or paralysis of, motor nerves

Anatomical features:

A hernia consists of:

A sac
Its coverings
Its contents

The sac comprises a:

Mouth
Neck
Body
Fundus

The coverings of a hernia refer to the overlying layers which are attenuated as the hernia emerges. Working from the outermost layer inwards, these are as follows:

Skin
Subcutaneous fat
Aponeurosis
Muscle
Endo-cavity fascia
Endothelial lining (peritoneum in the abdomen)

The contents of hernias vary, but most intracavity viscera have been reported. In the abdomen, the commonest contents are the small bowel and the greater omentum. Other possibilities include:

The large bowel and appendix
Meckel’s diverticulum
The bladder
The ovary (with or without the fallopian tube)
Ascetic fluid

Natural history and complications:

The natural history of hernia development is progressive enlargement, not spontaneous regression. With the passage of time, the likelihood of a life-threatening complication increases.

Hernias may be:

Reducible
Irreducible
Obstructed
Strangulated
Inflamed

Reducible hernia:

The contents can be returned from whence they came, but the sac persists
The contents do not necessarily reappear spontaneously, but do so when assisted by gravity or raised intra-abdominal pressure

Irreducible hernia:

The contents cannot be returned to the body cavity in this type of hernia. The causes of irreducibility are:

Narrow neck with rigid margins, often in association with a capacious sac (e.g. femoral, umbilical)
Adhesion formation between the contents and the sac (usually long-standing hernias)

Irreducible hernias have a greater risk of obstruction and strangulation than do reducible ones

Obstructed hernia:

Contains intestine in which the lumen has been occluded
Obstruction is usually at the neck of the sac but may be caused by adhesions within it
If the obstruction is at both ends of the loop, fluid accumulates within it and distension occurs (closed-loop obstruction)
Initially, the blood supply to the obstructed loop of bowel is intact, but with time this becomes impeded and strangulation supervenes
The term ‘incarcerated’ is sometimes used to describe a hernia that is irreducible but not strangulated. Thus, an irreducible, obstructed hernia can also be called an incarcerated one

Strangulated hernia:

10% of groin hernias present for the first time with strangulation
The blood supply to the contents of the hernia is cut off
The pathological sequence is:

Venous/lymphatic occlusion and oedema causing further swelling
Venous haemorrhage develops and a vicious circle is set up, with swelling eventually impeding arterial inflow
The tissues undergo ischaemic necrosis

If the contents of the sac of an abdominal hernia are NOT bowel (e.g. omentum) then the necrosis is sterile, but strangulation of bowel is by far the most common and leads to infected necrosis (gangrene):

The mucosa sloughs
Bowel wall becomes permeable to bacteria
The bacteria translocate through the wall and into the sac and from there into the bloodstream and peritoneal cavity (causing peritonitis)
Septic shock ensues with circulatory failure and death

Inflamed hernia:

The contents of the sac are inflamed by any process that causes this in the tissue or organ that is not normally herniated, e.g.:

Acute appendicitis
Meckel’s diverticulum
Acute salpingitis

It may be impossible to distinguish an inflamed hernia from one that is strangulated

Surgical techniques:

Herniotomy:

Is the removal of the sac and closure of its neck
It is the first step in nearly every hernia repair

Herniorrhaphy – involves some sort of reconstruction to:

Restore the anatomy if this is disturbed
Increase the strength of the abdominal wall
Construct a barrier to recurrence

Prognosis:

Mortality:

For elective repair, the overall mortality is <0.5%
Increases with age to 0.5-1% for those over 60 years of age
For emergency operations, the mortality is 10x greater
Mortality for strangulated hernia is ~20%. Death is dependent on:

Age
Contents of the sac – gangrenous intestine (present in 10% of strangulated hernias) is associated with a 40% mortality rate

Morbidity:

The overall complication rate is ~7%
Specific complications include:

Persistent wound pain – often ascribed to a neuroma which forms after damage to or division of the ilio-inguinal or other nerve
Cutaneous anaesthesia – division of a nerve
Recurrent hernia

The rate of recurrence is between 1-10% for primary hernias and 5-30% for recurrent hernias. Recurrence is associated with:

Age
Presence or absence of predisposing factors
Site
Size – the larger the hernia, the more likely it is to have distorted the surrounding anatomy
Emergency or elective operation – more likely to recur with an emergency procedure
Operation on a recurrent hernia – more difficult and more likely to fail
Experience of the surgeon


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	Hernia Definition: A hernia is a ‘protrusion of a viscus or other structure beyond the normal coverings of the cavity in which it is contained or between two adjacent cavities, such as the abdomen and the thorax, or into a subcompartment of a cavity’ The first category is commonly called external and the second and third are internal The most frequent hernias are external ones of the abdominal wall in the: Inguinal Femoral Umbilical, regions Classification Hernias are best classified as congenital or acquired Congenital: There is a pre-formed sac which occurs as a consequence of the ordered or disordered process of intra-uterine development The patent processus vaginalis is a good example Acquired – are 2 types: Primary hernias – occur at natural weak points Secondary hernias – develop at sites of surgical or other injury to the wall which normally constrains the contents of a body cavity (usually the abdomen) Aetiology: The 2 main factors predisposing to hernia are increased intracavity pressure and a weakened abdominal wall. Using the abdomen as an example: Increased intra-abdominal pressure: Heavy lifting Persistent cough (e.g. COAD) Straining to pass urine (e.g. BPH) Straining to pass faeces (>15% of men with large bowel cancer present with an inguinal hernia) Abdominal distension (faeces, fat, flatus, fluid, foetus) Weakened abdominal wall: Abnormal collagen metabolism Advancing age Malnutrition Damage to, or paralysis of, motor nerves Anatomical features: A hernia consists of: A sac Its coverings Its contents The sac comprises a: Mouth Neck Body Fundus The coverings of a hernia refer to the overlying layers which are attenuated as the hernia emerges. Working from the outermost layer inwards, these are as follows: Skin Subcutaneous fat Aponeurosis Muscle Endo-cavity fascia Endothelial lining (peritoneum in the abdomen) The contents of hernias vary, but most intracavity viscera have been reported. In the abdomen, the commonest contents are the small bowel and the greater omentum. Other possibilities include: The large bowel and appendix Meckel’s diverticulum The bladder The ovary (with or without the fallopian tube) Ascetic fluid Natural history and complications: The natural history of hernia development is progressive enlargement, not spontaneous regression. With the passage of time, the likelihood of a life-threatening complication increases. Hernias may be: Reducible Irreducible Obstructed Strangulated Inflamed Reducible hernia: The contents can be returned from whence they came, but the sac persists The contents do not necessarily reappear spontaneously, but do so when assisted by gravity or raised intra-abdominal pressure Irreducible hernia: The contents cannot be returned to the body cavity in this type of hernia. The causes of irreducibility are: Narrow neck with rigid margins, often in association with a capacious sac (e.g. femoral, umbilical) Adhesion formation between the contents and the sac (usually long-standing hernias) Irreducible hernias have a greater risk of obstruction and strangulation than do reducible ones Obstructed hernia: Contains intestine in which the lumen has been occluded Obstruction is usually at the neck of the sac but may be caused by adhesions within it If the obstruction is at both ends of the loop, fluid accumulates within it and distension occurs (closed-loop obstruction) Initially, the blood supply to the obstructed loop of bowel is intact, but with time this becomes impeded and strangulation supervenes The term ‘incarcerated’ is sometimes used to describe a hernia that is irreducible but not strangulated. Thus, an irreducible, obstructed hernia can also be called an incarcerated one Strangulated hernia: 10% of groin hernias present for the first time with strangulation The blood supply to the contents of the hernia is cut off The pathological sequence is: Venous/lymphatic occlusion and oedema causing further swelling Venous haemorrhage develops and a vicious circle is set up, with swelling eventually impeding arterial inflow The tissues undergo ischaemic necrosis If the contents of the sac of an abdominal hernia are NOT bowel (e.g. omentum) then the necrosis is sterile, but strangulation of bowel is by far the most common and leads to infected necrosis (gangrene): The mucosa sloughs Bowel wall becomes permeable to bacteria The bacteria translocate through the wall and into the sac and from there into the bloodstream and peritoneal cavity (causing peritonitis) Septic shock ensues with circulatory failure and death Inflamed hernia: The contents of the sac are inflamed by any process that causes this in the tissue or organ that is not normally herniated, e.g.: Acute appendicitis Meckel’s diverticulum Acute salpingitis It may be impossible to distinguish an inflamed hernia from one that is strangulated Surgical techniques: Herniotomy: Is the removal of the sac and closure of its neck It is the first step in nearly every hernia repair Herniorrhaphy – involves some sort of reconstruction to: Restore the anatomy if this is disturbed Increase the strength of the abdominal wall Construct a barrier to recurrence Prognosis: Mortality: For elective repair, the overall mortality is <0.5% Increases with age to 0.5-1% for those over 60 years of age For emergency operations, the mortality is 10x greater Mortality for strangulated hernia is ~20%. Death is dependent on: Age Contents of the sac – gangrenous intestine (present in 10% of strangulated hernias) is associated with a 40% mortality rate Morbidity: The overall complication rate is ~7% Specific complications include: Persistent wound pain – often ascribed to a neuroma which forms after damage to or division of the ilio-inguinal or other nerve Cutaneous anaesthesia – division of a nerve Recurrent hernia The rate of recurrence is between 1-10% for primary hernias and 5-30% for recurrent hernias. Recurrence is associated with: Age Presence or absence of predisposing factors Site Size – the larger the hernia, the more likely it is to have distorted the surrounding anatomy Emergency or elective operation – more likely to recur with an emergency procedure Operation on a recurrent hernia – more difficult and more likely to fail Experience of the surgeon
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