Internal Abdominal Herniations

An internal abdominal herniation is the protrusion of an abdominal organ through a normal or abnormal mesenteric or peritoneal aperture. An internal abdominal herniation differs from both an external abdominal herniation, in which the protrusion occurs through an opening of the abdominal wall, and a diaphragmatic herniation, which involves a weakness of the diaphragm. Internal abdominal herniations can be either acquired through a trauma or surgical procedure (iatrogenic internal abdominal herniations) or constitutional and related to congenital peritoneal defects.

Because internal abdominal herniations are rare, their diagnosis remains a challenge for both the clinician and the radiologist. Symptoms of internal abdominal herniations are nonspecific, consisting of mild abdominal discomfort alternating with episodes of intense periumbilical pain and nausea. CT is believed to facilitate the diagnosis of internal abdominal herniations. Specific signs of internal abdominal herniations on CT have been previously reported. The use of CT could limit the rate of misdiagnosed internal abdominal herniations because subtle transmesenteric internal abdominal herniations can be difficult to diagnose on laparoscopy.

This pictorial essay focuses on constitutional internal abdominal herniations (excluding iatrogenic and surgical internal herniations). We review the main mechanisms of internal abdominal herniations and the main radiologic findings on barium as well as CT studies.

Classification

The classifications of internal abdominal herniations devised by Ghahremani [5] is now well accepted. According to this classification system, internal abdominal herniations can be separated in six main groups: paraduodenal hernias (50–55% of internal abdominal herniations), hernias through the foramen of Winslow (6–10%), transmesenteric hernias (8–10%), pericecal hernias (10–15%), intersigmoid hernias (4–8%), and paravesical hernias (< 4%).

Fig. 1. —Illustration shows typical locations of different types of internal abdominal herniations: 1 = paraduodenal, 2 = foramen of Winslow, 3 = transmesenteric, 4 = pericecal, 5 = intersigmoid, 6 = paravesical (pelvic).

Paraduodenal Hernias

Two types of paraduodenal hernias must be distinguished: left-sided paraduodenal hernias, which account for 75% of all paraduodenal hernias, and right-sided paraduodenal hernias, which account for the remaining 25%.

Left-Sided Paraduodenal HerniasIn left-sided paraduodenal hernias, small-bowel loops herniate into an unusual fossa to the left of the duodenum referred to as the paraduodenal fossa, or Landzert's fossa, that results from a congenital defect in the descending mesocolon. This abnormal peritoneal pocket is bordered anteriorly by a peritoneal fold overlying the inferior mesenteric vein and ascending left colic artery. Proximal small-bowel loops, duodenal segments, or even, in rare cases, distal ileal segments enter posteriorly through the mesocolic defect, become entrapped in the Landzert's fossa, and then extend further in the descending mesocolon. Fig 2: Illustrations detail development of left-sided paraduodenal hernia. Small-bowel loops herniate into descending mesocolon through paraduodenal fossa posterior to inferior mesenteric vein and ascending left colic artery.

Fig 3: Illustrations detail development of left-sided paraduodenal hernia. Small-bowel loops progressively herniate through abnormal peritoneal pocket.

Fig 4:Illustrations detail development of left-sided paraduodenal hernia. Both inferior mesenteric vein and left ascending colic artery always remain anterior to neck of herniated sac in left-sided paraduodenal hernia.