Incisional Hernia

An incisional hernia is a hernia that occurs through a previously made incision in the abdominal wall.

They occur by definition after an operation, and are a remarkably common complication of abdominal surgery, with recent data reporting a prevalence after 1 year at 5.2% and 2 years at 10.3%.

In this article, we shall look at the risk factors, clinical features and management of an incisional hernia.


Pathophysiology

A hernia is defined as ‘the protrusion of a viscus, or part of a viscus through the wall of the cavity in which it is contained’.

The layers of the anterior abdominal wall are normally strong, and act to maintain the integrity of the abdominal cavity. However, once these layers are interrupted by a surgical incision, their continuity is disrupted, and they are weakened.

In the presence of increased intra-abdominal pressure and/or certain risk factors, the contents of the abdomen are able to herniate through the weakness, forming an incisional hernia.

As with any hernia, complications can occur – such as incarceration (hernia is irreducible), strangulation (blood supply to the hernia is compromised), or bowel obstruction.

Fig 1 - The muscles of the anterior abdominal wall.

Fig 1 – The muscles of the anterior abdominal wall.


Risk Factors

The risk factors for incisional hernia following abdominal surgery include (ranked by relative risk):

  • Emergency surgery
    • Emergency surgery carries double the risk of elective surgery.
  • Wound type
  • BMI >25
    • Obese patients are more likely to develop an incisional hernia
  • Midline incision
    • There is a 74% risk increase compared to non-midline
  • Wound infection
    • This increases incisional hernia risk by 68%.
  • Pre-operative chemotherapy
  • Intra-operative blood transfusion
  • Advancing age
  • Pregnancy

Other less common risk factors include chronic cough, diabetes mellitus, steroid therapy, smoking, and connective tissue disease.


Clinical Features

The characteristic clinical feature of an incisional hernia is a non-pulsatile, reducible, soft and non-tender swelling at or near the site of a previous surgical wound.

If the hernia is incarcerated, it can become painful, tender, and erythematous. In cases of bowel obstruction, the patient may also present with symptoms of abdominal distention, vomiting, and/or absolute constipation.

On examination, a mass is palpable at or near the site of the surgical incision, which may be reducible (depending on its severity). Assess the patient for any signs of bowel ischaemia (strangulation) – such as rebound tenderness or involuntary guarding.

Fig 2 - Large incisional hernia following surgery to remove a kidney stone.  A) Patient at time of presentation. B) Hernia in the supine position.

Fig 2 – Large incisional hernia following surgery to remove a kidney stone. A) Patient at time of presentation. B) Hernia in the supine position.


Differential Diagnosis

A history of previous surgery with herniation at or near the site of incision is characteristic of an incisional hernia – and leaves a very narrow differential diagnosis:

  • Other types of hernia – these can be differentiated from an incisional hernia by their location and an absence of surgical history.
  • Other causes of abdominal lumps – e.g lipoma.

Investigations

In most cases of incisional hernia, the diagnosis is made on a clinical basis – with no laboratory or imaging studies required.

Any features of complications from the hernia should be investigated accordingly (for example an abdominal X-ray to investigate for signs of bowel obstruction).

Ultrasound or MRI can be used to investigate a hernia if the diagnosis is unclear, as they can demonstrate a fascial gap with protruding abdominal contents. The sonographer often requests the patient to cough or Valsalver while scanning to demonstrate this.


Management

The management of an incisional hernia should be considered on a case-by-case basis. Initially it is possible to manage small asymptomatic hernias with watchful waiting, but they often enlarge.

Surgery is indicated in patients who are clinically fit enough for surgery and for whom the operation is likely to have beneficial results. The size of the hernia, the clinical features, the patient’s age and co-morbidities, and the patient’s preferences should all be taken into account.

Surgical Repair of an Incisional Hernia

Incisional hernias can be repaired using a variety of techniques, including suture repair, laparoscopic mesh repair, and open mesh repair.

In general, the smallest hernias (<3cm) can be managed by primary tissue approximation with non-absorbable sutures, whilst larger defects often require meshing.

Note: The debate between laparoscopic and open approach mesh repair continues. A recent study found laparoscopic mesh repair to significantly increase the risk of post-operative complications and require a longer operative time compared to open repair. However, it was associated with reduced intra-operative blood loss and reduced requirement for wound drains.

Prognosis

Incisional hernias are associated with a considerable risk of life-threatening complications; 6-15% of them incarcerate and 2% progress to strangulation.

Despite recent advances in techniques, recurrence rates remain high. They can be as high as 54% in suture repair and 36% in mesh repair, with an overall average at around 15%.

Chronic pain is a recognised but poorly understood complication of incisional hernia repair. It is thought to involve a combination of mesh inflammation, nerve damage and entrapment, and tension in the mesh. It affects 10-20% of cases.

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