Internal hernia

An internal hernia is the protrusion of visceral contents through a congenital or acquired defect in the peritoneum or mesentery within the abdominal cavity. Internal hernias have an incidence of < 1% and are significantly less common than external hernias. Patients with a history of Roux-en-Y gastric bypass or liver transplant are especially at risk of internal hernia formation. Small bowel loops are the most common content of an internal hernia. For this reason, the typical clinical presentation is that of a mechanical small bowel obstruction (i.e., colicky abdominal pain, vomiting, constipation, abdominal distention). Contrast-enhanced CT scan is the imaging modality of choice in most cases, but surgical intervention is often required for definitive diagnosis and treatment. Incarceration or strangulation of internal hernias carries a high mortality rate; rapid diagnosis and surgical repair is therefore imperative.

• Internal hernias have an overall incidence of < 1%.

References:^[1]

Epidemiological data refers to the US, unless otherwise specified.

Internal hernias are a protrusion of visceral contents through a defect in the peritoneum or the mesentery :

• Congenital or acquired defect (e.g., postsurgical, especially following Roux-en-Y gastric bypass or liver transplant)
• Normal anatomic structure (e.g., foramen of Winslow)

References:^[2]

Internal hernias may be classified as congenital or acquired, or by location as follows:

• Paraduodenal hernia (most common): herniation of the small bowel through a congenital opening in the mesentery
• Pericecal hernia (second most common): herniation into the pericecal fossa
• Transmesenteric hernia and transmesocolic hernia: herniation through defects in the small or large bowel mesentery
• Transomental hernia: herniation through an opening in gastrocolic omentum
• Foramen of Winslow hernia: herniation of viscera through the foramen of Winslow (also called lesser sac hernias)
• Internal supravesical hernia: herniation through the peritoneum into the pelvis around the urinary bladder
• Intersigmoid hernia: small bowel herniates into a peritoneal pocket formed by two adjacent sigmoid segments and their mesentery
• Retroanastomotic hernia: small bowel herniation through a defect created by a surgical anastomosis

• Features of intermittent or acute bowel obstruction :
  • Abdominal pain (intermittent or acute; colicky)
  • Nausea and vomiting; especially postprandial
  • Constipation or obstipation
  • Abdominal distension
  • Decreased bowel sounds
• Evidence of bowel incarceration with subsequent strangulation :
  • Fever
  • Tachycardia, hypotension
  • Peritonitis (rebound tenderness, guarding)

References:^[1]

• Abdominal x-ray: nonspecific signs of bowel obstruction (e.g., distended loops of bowel, absent air in distal colon, air fluid levels proximal to obstruction)
• CT scan (best initial and gold standard imaging modality)
• Laparoscopy or laparotomy (confirmatory and therapeutic)

The diagnosis of an internal hernia is confirmed by laparoscopy in the majority of cases.

• Mechanical bowel obstruction
• Mesenteric ischemia
• Bowel perforation with secondary peritonitis
• See differential diagnosis of acute abdomen.

The differential diagnoses listed here are not exhaustive.

• Conservative management
  • Indications
    • No evidence of hemodynamic instability
    • No evidence of sepsis or peritonitis
  • Measures: See “Conservative management” in “Mechanical bowel obstruction.”
• Surgery: either open or laparoscopic
  • Indications
    • Evidence of hemodynamic instability
    • Evidence of sepsis or peritonitis
    • No signs of improvement on conservative management
  • Procedure: reduction of the hernia and closure of the peritoneal or mesenteric defect

If an internal hernia leads to incarceration, the mortality rate is ∼ 80%.

References:^[2]