INTERNAL ABDOMINAL HERNIATION
An internal abdominal herniation is the extension of an abdominal organ through a mesenteric or peritoneal aperture. These rare lesions can be congenital or acquired as a result of trauma or intra-abdominal surgery. There is an association of this lesion with intestinal malrotation. Internal abdominal herniations rarely present during childhood, even when the underlying cause is developmental. The clinical manifestations of internal abdominal herniation are nearly always nonspecific. Patients may report abdominal pain or discomfort that tends to be episodic. The pain is most often localized to the periumbilical region. Nausea may occur. Manifestations of an acute bowel obstruction develop if there is bowel incarceration. CT is the most useful diagnostic imaging study for the evaluation of internal abdominal herniations; contrast studies of the bowel and standard radiographs serve roles as well.1,2
Six types of intra-abdominal herniations are generally recognized: paraduodenal hernias, hernias through the foramen of Winslow, transmesenteric hernias, pericecal hernias, intersigmoid hernias, and paravesical hernias. Paraduodenal hernias are the most common type in adults; these are further subdivided into left- and right-sided types. Paraduodenal hernias result from a congenital deficiency in mesenteric peritoneal fixation.3–6
At least three-quarters of paraduodenal hernias occur on the left, with the peritoneal defect located to the left of the distal portion of the duodenum. Small intestine can herniate through this mesenteric defect into the left portion of the transverse mesocolon. Barium examinations show a cluster of slightly dilated loops of small bowel located just lateral to the distal portion of the duodenum and separated from normal small bowel elsewhere in the abdomen. On CT, the herniated small bowel loops are located between the stomach and the tail of the pancreas, posterior to the tail of pancreas, or between the transverse portion of the colon and the left adrenal gland.
Right-sided paraduodenal hernias are also congenital lesions. The pathogenesis involves failure of normal embryonic midgut rotation, resulting in positioning of the proximal aspect of the small bowel to the right of the superior mesenteric artery. With a hernia, this portion of the small bowel projects through a defect in the proximal jejunal mesentery dorsal to the mesenteric artery and directed toward the right-sided mesocolon. Barium studies and CT show the collection of herniated loops of small bowel to be located just lateral and inferior to the second portion of the duodenum. The herniated bowel is usually somewhat dilated.
The foramen of Winslow is a normal peritoneal opening that is located between the portal vein and inferior vena cava, and opens into the lesser sac. Herniations through an enlarged foramen of Winslow may consist of small bowel, colon, or gallbladder. On barium studies, herniated bowel within the lesser sac causes lateral and anterior displacement of the stomach. CT shows extension of bowel and/or mesenteric fat into the portocaval space between the inferior vena cava and portal vein.