Incarceration obstruction and strangulation

Incarceration is the state of an external hernia, which cannot be reduced into the abdomen. Incarceration is important because it implies an increased risk of obstruction and strangulation. Incarceration is caused by (a) a tight hernial sac neck; (b) adhesions between the hernial contents and the sac lining - these adhesions are sometimes a manifestation of previous ischaemia and inflammation; (c) development of pathology in the incarcerated viscus, e.g. a carcinoma or diverticulitis in incarcerated colon; (d) impaction of faeces in an incarcerated colon.

Incarceration is an important finding. It should urge the surgeon to undertake operation sooner rather than later. If reduction of a hernia is performed it should be gentle; forcible reduction of an incarcerated hernia may precipitate reductio-en-masse (see below). If bowel with a compromised blood supply is reduced, stricturing and adhesions between gut loops will follow. This will lead to intestinal obstruction some weeks or months later. The best policy is to operate on incarcerated hernias and check the viability of the gut at operation.

Incarceration in an inguinal hernia is the commonest cause of acute intestinal obstruction in infants and children in the UK. In adults, postoperative adhesions account for 40% of cases of obstruction, external hernias for 30% and malignancy for 25% of cases. In tropical Africa, strangulated external hernia is the commonest cause of intestinal obstruction in all age groups.

Patients presenting with symptoms of intestinal obstruction should have all the potential hernial sites very carefully examined. The sites of obstruction are inguinal, femoral, umbilical, incisional, Spigelian, and obturator and perineal hernial orifices in that order. A partial enterocoele (Richter's hernia) is a particularly treacherous variety of hernia, especially in infancy. Partial enterocoele is a potentially lethal and easily overlooked complication of 'port site' hernia following laparoscopy.

Strangulation is the major life-threatening complication of abdominal hernias. In strangulation the blood supply to the hernial contents is compromised. At first there is angulation and distortion of the neck of the sac; this leads to lymphatic and venous engorgement. The herniated contents become oedematous. Capillary vascular permeability develops. The arterial supply is occluded by the developing oedema and now the scene is set for ischaemic changes in the bowel wall.

The gut mucosal defenses are breached and intestinal bacteria multiply and penetrate through to infect the hernial sac contents. Necrobiosis and gangrene complete a sad and lethal cycle unless surgery or preternatural fistula formation save the patient. Hypovolaemia and septic shock predicate vigorous resuscitation if surgery is to be successful.

Forty per cent of patients with femoral hernia are admitted as emergency cases with strangulation or incarceration, whereas only 3% of patients with direct inguinal hernias present with strangulation. A groin hernia is at its greatest risk of strangulation within 3 months of its onset. The general public, especially the elderly, should be aware of the potential dangers of a lump in the groin. The most easily missed of these lumps in the groin is a femoral hernia in an obese patient in whom the consequences of a missed diagnosis carry a high morbidity and mortality.

Obturator hernias are very prone to strangulation; however, their elective repair is rarely feasible and a high index of suspicion particularly in elderly, emaciated female patients with symptoms of intestinal obstruction is required. Clinical

suspicion combined with preoperative ultrasonography or computed tomographic (CT) scan can correctly diagnose obturator hernia preoperatively and result in successful surgery:

• Incarceration should be treated urgently.

• External hernias are one of the commonest causes of intestinal obstruction.

• Strangulation should be treated emergently after adequate resuscitation.

• Femoral and obturator hernias frequently present with strangulation and should be considered in a patient with an unidentified cause for intestinal obstruction.

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