Of patients who present with acute intestinal obstruction, fewer than 5% have an internal hernia. When internal hernias are complicated by intestinal volvulus, there is an 80% incidence of strangulation or gangrene.
Internal hernias occur within the abdominal cavity owing to congenital or acquired causes. Congenital causes include abnormal intestinal rotation (paraduodenal hernias) and openings in the ileocecal mesentery (transmesenteric hernias). Other, less frequent types are pericecal hernias, hernias through the sigmoid mesocolon, and hernias through defects in the transverse mesocolon, gastrocolic ligament, gastrohepatic ligament, or greater omentum. Acquired causes include hernias through mesenteric defects created by bowel resections or ostomy formation. The small bowel may also herniate beneath an adhesion from previous surgery.
Clinical presentation. These hernias usually are diagnosed because an intestinal segment becomes incarcerated within the internal defect, resulting in small-bowel obstruction. Patients with congenital causes usually have not had prior abdominal surgery. The reported mortality in acute intestinal obstruction secondary to internal hernias is 10% to 16%. Symptoms usually are of intestinal obstruction without evidence of an external hernia. When there is intestinal obstruction or intestinal strangulation, the diagnosis is based on clinical rather than on laboratory findings.
Radiographic studies. Plain abdominal films may show small-bowel obstruction. An abdominal CT scan can sometimes establish the diagnosis of an internal hernia preoperatively. Contrast studies may also sometimes be useful.
D. Differential diagnosis
Differential diagnosis includes other causes of intestinal obstruction, such as adhesions, external hernia, malignancy, gallstone ileus, and intussusception.