Chapter 402. Omphalo-Mesenteric Duct Remnants

An “unusual” diverticulum of the small intestine was first described by Fabricius Hildanus in 1598, but Johannes Meckel wrote the first definitive description of the Meckel diverticulum in 1809. The vitelline (or omphalo-mesenteric) connects the yolk sac to the primitive gut. It normally involutes by the ninth week of gestation, but persistence of all or portions of this duct can result in a Meckel diverticulum or other abnormalities of the omphalomesenteric duct, such as omphalomesenteric fistula, omphalomesenteric cyst, umbilical sinus, or mesodiverticular bands.1

Epidemiology

Meckel diverticulum is the most common congenital abnormality of the small intestine, occurring in 2% of the population. In general, Meckel diverticulum follows the rule of twos: affects 2% of the population; most commonly found 2 feet from the ileocecal valve; 2 types of ectopic tissue are found within the diverticulum (gastric and pancreatic tissue); and 2% develop symptoms. In fact, the life-time risk of complications from Meckel diverticulum has been estimated to be between 4% and 6%.2 Given the low number of symptomatic diverticula, many Meckel diverticula are identified incidentally during operations for other pathology. While most Meckel diverticula are sporadic, there is an association with Hirschsprung disease, Down syndrome, esophageal atresia, duodenal atresia, malrotation, and congenital cardiac abnormalities.3 Other omphalomesenteric duct abnormalities are much less common.

Pathophysiology and Genetics

Normal gut development depends on the interactions among the layers of endoderm (epithelial lining), mesoderm (smooth muscle formation) and ectoderm (enteric nervous system). Histologically, a Meckel diverticulum is a true diverticulum, consisting of all four intestinal layers. The blood supply is a vestige of the primitive vitelline artery and may be prominent in patients with bleeding presentations (see Fig. 402-1). Murine studies noted formation of buds at the region of the vitelline duct in approximately 3% of 13.5-day embryos. The tissue from these buds was able to express albumin; the remainder of the surrounding tissue did not, suggesting an escape from the inhibitory effects of the mesoderm.4 Further studies are necessary to delineate the complex pathway leading to the development of a Meckel diverticulum.

Clinical Features and Differential Diagnosis

The most common presentations of symptomatic a Meckel diverticulum include painless lower gastrointestinal (GI) bleeding, inflammation with or without perforation, or bowel obstruction from volvulus, intussusception, or internal hernia (see Fig. 402-1). Such presentations often mimic other pathology requiring emergent surgery and therefore diagnosis of a Meckel diverticulum is often made only in the operating room.

GI bleeding is the most common presenting symptom associated with a Meckel diverticulum, and it is the most common cause of massive lower GI bleeding in children less than 4 years of age (see Chapter 387). Ectopic gastric mucosa causes ulceration of the adjacent mucosa with resultant bleeding. Patients typically present with relatively painless rectal bleeding. The blood loss can be brisk and associated with significant anemia and hypotension. This can mimic intussusception as well as other sources of lower GI bleeding.

Meckel diverticulitis typically presents with abdominal pain, fever, and leukocytosis. Signs of peritonitis and sepsis are often present if diagnosis is delayed. Presentation is often indistinguishable from acute appendicitis. Bowel obstruction from a Meckel diverticulum or omphalomesenteric duct remnant presents with abdominal distension and pain. Most often obstruction is associated with bilious emesis and absence of stools and flatus. Signs of dehydration due to intravascular depletion are common. Signs of peritonitis and sepsis are worrisome for ischemic or necrotic bowel as a consequence of a strangulated bowel obstruction. Preoperative differentiation from other causes of obstruction—adhesions, hernias, congenital bands, etc—can be difficult and is unnecessary.

Diagnostic Evaluation

The approach to evaluation of the child with varies depending upon the clinical presentation. Meckel diverticulus presents with inflammation, with or without perforation, pain and possibly signs of peritonitis associated with a fever and leukocytosis. In this setting, physical examination may dictate emergent operative exploration without the need for further diagnostic evaluation. Ultrasonography or computed tomography of the abdomen and pelvis typically demonstrate signs of inflammation, free fluid or free air and occasionally an edematous, inflamed blind ending segment of bowel in the right lower quadrant of the abdomen to suggest Meckel’s diverticulitis. Theses findings on ultrasound and computed tomography scan often mimic that of appendicitis. The approach to the child with bowel obstruction is discussed in Chapter 389.

The approach to a child with gastrointestinal (GI) bleeding is described in Chapter 387. If a Meckel diverticulum is suspected, a technetium 99m pertechnetate scintigraphy, also known as a Meckel scan is used to demonstrate the presence of gastric epithelium which concentrates the radio-labeled pertechnetate (see Fig. 402-2). This can be enhanced by the administration of an H2 receptor antagonist and pentagastrin. The sensitivity of Meckel’s scan is 85%, and specificity is 95%. The Meckel’s scan has a high false negative rate even in patients with gastric mucosa demonstrated on pathological examination.5 The probability of a Meckel diverticulum as the source of the GI bleeding in a child who presents with a GI bleed, hemoglobin less than 11g/dL and a negative Meckel’s scan is 0.26.5 For this reason, as well as the low morbidity associated with diagnostic laparoscopy, patients with a significant GI bleed with no source identified following less invasive diagnostic tests should be considered for diagnostic laparoscopy despite a negative Meckel’s scan (see eFig. 402.1).

Treatment

Management of patients with symptomatic complications of a Meckel diverticulum or other omphalomesenteric duct remnants is surgical, and surgical consultation should be sought early in the treatment.6 Removal of the diverticulum, cyst, or fistula and any associated ectopic gastric tissue must be ensured in order to prevent recurrent bowel obstruction, bleeding and/or ulcers, and diverticulitis. A narrow-based diverticulum and those with gastric tissue at the tip of the diverticulum may be resected at the base, whereas wide-based and short diverticula require resection of additional small bowel in order to ensure removal of all gastric mucosa.

A diverticulectomy, wedge resection, or partial small bowel resection may be performed open or laparoscopically. Whether the abdomen is explored via laparotomy or with the laparoscope, evaluating the terminal ileum and working proximally will identify a Meckel diverticulum if present. Laparoscopic methods have been described and include a camera port with 2 to 3 working ports. Alternatively, a single 10-mm trocar placed at the umbilicus and an operative telescope have been used to grasp the terminal ileum and exteriorize the Meckel diverticulum through the umbilical incision for resection.7

Controversy exists as to the management of an asymptomatic Meckel diverticulum found incidentally at the time of a laparotomy. The risk of development of symptoms in the future is inversely related to the patient’s age. Most pediatric surgeons would remove an asymptomatic Meckel diverticulum in an infant or child at the time of laparotomy unless it may increase the risk of postoperative complications. Meckel diverticula that contain palpable ectopic mucosa, appear inflamed, are attached to the umbilicus, or have a narrow base are more likely to cause symptoms if left in place and therefore are often removed. In older children and adults, the risk of developing complications from an unresected Meckel diverticulum appears less likely, and the risk of future complications if the Meckel diverticulum is left in place must be weighed on an individual basis against the risk of complications from resection.

Complications from surgical resection are infrequent with an incidence of less than 1% to 2%. Patients who have undergone resection of a Meckel diverticulum typically have no further problems.

Meckel’s diverticulum is the most common remnant of the omphalomesenteric duct. Other remnants of the duct can cause symptoms (Fig. 402-1). The obliterated duct can remain attached to the abdominal wall and provides a pedicle around which the bowel can twist with resultant volvulus. Umbilical granulomas are small, 1 mm to 1 cm pink friable lesions at the base of the umbilicus that produce drainage that may irritate the surrounding skin. An umbilical polyp is bright red and contains retained gastric or intestinal mucosa from the vitelline duct. As discussed above, Meckel diverticulum and other omphalomesenteric ductal remnants may cause bowel obstruction. They may also remain patent, from the terminal ileum to the umbilicus, such that fecal umbilical drainage is observed.5 An omphalomesenteric sinus and cyst may present with episodes of recurrent abdominal pain, sometimes being relieved with the discharge of contents from the umbilicus. These lesions are diagnosed by physical examination and fistulogram when an umbilical opening is evident. An omphalomesenteric cyst can occasionally be diagnosed by ultrasound. However, similar to Meckel Diverticulum, these remnants often present with inflammation with or without perforation, or bowel obstruction from volvulus, intussusception, or internal hernia and diagnosis is made in the operating room. Treatment is by surgical excision.