Internal Hernia

An internal hernia is protrusion of bowel through a congenital or acquired intraperitoneal or mesenteric aperture while remaining within the abdominal cavity.

Major types include paraduodenal, transmesenteric, transomental, pericaecal, sigmoid mesocolon, foramen of Winslow and postoperative internal hernias.

Acquired mesenteric defects are particularly important after Roux en Y gastric bypass, bowel reconstruction and transplantation.

Internal hernias frequently create a closed loop obstruction, making strangulation and bowel infarction the major concern.

Presentation ranges from intermittent spontaneously resolving abdominal pain to complete bowel obstruction with strangulation.

Patients may report recurrent episodes of central or upper abdominal pain, often associated with nausea and vomiting.

Acute closed loop obstruction produces severe pain, vomiting and progressive abdominal tenderness.

Persistent pain, tachycardia, focal guarding, gastrointestinal bleeding, metabolic deterioration or peritonism suggests bowel ischaemia.

A history of previous gastric bypass or complex bowel reconstruction should markedly increase suspicion even when the examination is initially mild.

CT abdomen and pelvis with IV contrast: investigation of choice; look for clustered displaced bowel loops with convergence or twisting of mesenteric vessels at an abnormal internal aperture and determine whether a closed loop is present.

A negative CT does not completely exclude an intermittent postoperative internal hernia. Recurrent severe symptoms after Roux en Y reconstruction require a low threshold for surgical assessment.

An internal hernia causing acute obstruction requires early operative management because deterioration from obstruction to strangulation can be rapid.

Keep fasting, establish IV access, correct fluid and electrolyte deficits and use nasogastric decompression when significant vomiting or distension is present.

Do not undertake a prolonged conservative trial when CT demonstrates an internal hernia with a closed loop or when clinical suspicion for strangulation is high.

Laparoscopy is appropriate in stable patients with manageable bowel distension. Laparotomy is preferable when there is haemodynamic instability, massive distension, established peritonitis or anticipated extensive bowel resection.

At operation:

• Reduce the herniated bowel carefully
• Assess the entire involved segment for viability
• Identify the anatomical defect
• Close the defect securely
• Resect irreversibly ischaemic bowel

All relevant mesenteric defects should be inspected in patients with previous reconstructive surgery because more than one potential internal aperture may exist.

If bowel viability is uncertain after reduction, allow time for reperfusion and reassess. Extensive questionable bowel should not be unnecessarily resected. A planned second look operation may be appropriate when viability remains uncertain.

If ischaemic or perforated bowel is present, begin enteric Gram negative and anaerobic coverage, for example:

Ceftriaxone 2 g IV every 24 hours plus metronidazole 500 mg IV every 12 hours.

Severe sepsis or extensive contamination can be treated with:

Piperacillin tazobactam 4.5 g IV every 8 hours by extended infusion, adjusted for renal function.