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Special Feature
July 1, 2006

Image of the Month—Diagnosis

Arch Surg. 2006;141(7):711-712. doi:10.1001/archsurg.141.7.712
Answer: Paraduodenal Hernia

In the case of this patient, we traced the small bowel back to a transition point where herniation through a defect in the transverse colonic mesentery was found. This defect was identified to be in the left paraduodenal space. Therefore, this defect was opened laterally, taking care to protect the vessels at the hernia sac margin. The herniated bowel (approximately half of the small bowel) was reduced and inspected carefully for viability. The hernia defect was repaired with a running vicryl stitch, and once again avoiding the vessels at the mouth of the defect. The patient recovered well and was having normal bowel movements by postoperative day 5. At the 3-week postoperative follow-up examination, all symptoms had resolved and the patient had no complaints.

Internal hernias are uncommon and difficult to diagnose clinically. They are defined as the herniation of a viscus through an intraperitoneal orifice or aperture within the confines of the peritoneal cavity. The orifice may represent normal anatomy (foramen of Winslow), abnormal anatomy (paraduodenal, ileocecal), pathologic anatomy (orifice formed in a mesentery or omentum), or an anomalous orifice.1

Incidence of internal hernia has been variably reported to be 1% to 2%.1,2It may be discovered incidentally at autopsies or at exploratory laparotomy. Clinical manifestations are variable, ranging from chronic dyspepsia to acute or chronic obstruction and, if strangulation occurs, bowel infarction.2Internal hernias are an uncommon cause of small-bowel obstruction with a reported incidence of 0.2% to 0.9%.1

About 50% of internal hernias reported in the literature have been paraduodenal.1,2They are also known as mesocolic or mesentericoparietal hernias and are a result of congenital variations in the peritoneal fixation and vascular folds.3This hernia escapes through a small posterior wall opening to gain access to the space behind the mesentery or behind the descending mesocolon. This may contain widely variable lengths of the small bowel.4

It was formerly thought that these lesions were acquired and that the sacs were produced by intestines forcing their way into some small recess or indentation below the ligament of Treitz. Such a theory is scarcely plausible because there is insufficient differential pressure within the confines of the abdominal wall to allow such a dissection to take place. The more recent studies rather conclusively support the view that these pouches are always congenital in origin and that they result from an incomplete posterior fixation of the mesentery and mesocolon.4As the midgut rotates in fetal life, the mesentery becomes fused to the posterior abdominal structures from the ligament of Treitz inferolaterally toward the right iliac fossa. This process of attachment may be complete except for a small zone just below the duodeno-jejunal junction where the former emerges from its retroperitoneal position. The pocket thus formed may extend to the right behind the mesentery, behind the ascending colon, or up behind the transverse mesocolon. Conversely, the pocket may extend to the left behind the descending mesocolon and descending colon. When bowel enters these 2 spaces, the resulting lesions are called right or left paraduodenal hernias.

Five paraduodenal hernias have been described and thought to occur in the tenth gestational week. Despite their congenital nature, paraduodenal hernias usually become symptomatic in adults at an average age of 38.5 years.2Seventy-five percent of paraduodenal hernias occur on the left and 25% on the right.1,2

The left-sided paraduodenal hernia occurs when the small bowel herniates through the fossa of Landzert.2It has a mass lying largely to the left of the vertebral column and an orifice facing the right, which often displaces the stomach superiorly and the transverse colon inferiorly.1,4Right paraduodenal hernias are similarly ovoid but are located on the right and displace the ascending colon anterolaterally. Barium studies and computed tomographic scans of these hernias may also show the point of transition where the bowel loops enter and exit the orifice. Angiographic images reveal an altered course of the jejunal vessels as they course along the herniated portions of bowel.1

The inferior mesenteric artery and vein course along the anterior and inferior border of the left paraduodenal hernia. The superior mesenteric artery and vein lie in or near the anterior border of the constricting ring of the right paraduodenal hernia. The positions of these vessels are important for 2 reasons. First, stretching of the hernial ring by entrapped viscera may compress the blood vessels and bring about extensive infarction of the intestine or colon. Second, care must be taken in dividing the constricting ring during surgical reduction of the hernia.4

Treatment is based on reduction of the hernia, ensuring viability of bowel with possible resections, and closure of the defect (again, carefully protecting the surrounding vasculature).

It is impossible to establish the correct diagnosis with physical examination alone. The abdominal cavity should be explored once a diagnosis of acute complete small-bowel obstruction is made. Hence, it is important for the surgeon to be familiar with the various internal hernias so as to recognize them intraoperatively and institute the appropriate therapeutic measures without delay.

Correspondence:R. Ramesh Singh, MD, University of Virginia Hospital, PO Box 800136, Charlottesville, VA 22908 (rs2dj@virginia.edu).

Accepted for Publication:June 6, 2005.

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