Meckel's diverticulum

Meckel's diverticulum
Caption	Diagram showing a Meckel's diverticulum (center left) connected to the ileum.
Field	General surgery, Pediatric surgery, Gastroenterology

Meckel's diverticulum. It is the most common congenital malformation of the gastrointestinal tract, resulting from incomplete obliteration of the vitelline duct (also known as the omphalomesenteric duct) during fetal development. This true diverticulum, containing all layers of the intestinal wall, is typically located on the antimesenteric border of the distal ileum. While often asymptomatic, it can lead to significant complications, particularly in children, due to the presence of heterotopic tissue such as gastric mucosa or pancreatic tissue.

Overview

A Meckel's diverticulum is a vestigial remnant of the embryonic vitelline duct, which normally connects the developing midgut to the yolk sac. The condition follows "Rule of 2s": it is found in about 2% of the population, is usually located within 2 feet (60 cm) of the ileocecal valve, is often about 2 inches (5 cm) in length, and commonly becomes symptomatic before age 2, though it can present at any age. Its clinical significance was first described by the German anatomist Johann Friedrich Meckel the Younger in 1809. The potential for complications arises primarily from ectopic tissue, with gastric mucosa being present in a significant proportion of symptomatic cases, which can secrete hydrochloric acid and lead to ulceration.

Signs and symptoms

The majority of individuals with a Meckel's diverticulum remain asymptomatic throughout life. When symptoms occur, they often mimic other common abdominal emergencies. Painless rectal bleeding, typically maroon or brick-red, is a classic presentation in young children, resulting from acid-secreting gastric mucosa causing ulceration in the adjacent ileal mucosa. Other presentations include intestinal obstruction due to intussusception, volvulus, or internal herniation around a fibrous band connecting the diverticulum to the umbilicus (a remnant of the vitelline duct). Inflammation of the diverticulum, known as Meckel's diverticulitis, presents similarly to appendicitis, with right lower quadrant pain, fever, and nausea. Rarely, it can be a lead point for intussusception or perforate, leading to peritonitis.

Pathophysiology

The embryological origin lies in the vitelline duct, which typically involutes between the 5th and 7th weeks of gestation. Failure of complete obliteration results in various anomalies, with a Meckel's diverticulum being the most common. The presence of heterotopic tissue is a key pathophysiological driver; gastric mucosa is found in approximately 50% of symptomatic specimens and 5-16% of asymptomatic ones. This tissue contains parietal cells that secrete acid and pepsin, leading to mucosal ulceration and bleeding in the adjacent alkali-sensitive ileal mucosa. Pancreatic acinar tissue is another less common ectopic type. Complications like obstruction often involve fibrous bands or the diverticulum itself acting as a point of fixation, leading to volvulus or intussusception.

Diagnosis

Diagnosis can be challenging due to its nonspecific presentation. A technetium-99m pertechnetate scan, often called a "Meckel scan," is the imaging study of choice for identifying ectopic gastric mucosa. The radiotracer is taken up by mucin-secreting cells of the gastric mucosa and can detect a diverticulum with high sensitivity, especially in children. Premedication with H2 receptor antagonists like cimetidine or ranitidine, or proton pump inhibitors like omeprazole, can enhance sensitivity by reducing tracer secretion. Other modalities include computed tomography (CT) or magnetic resonance imaging, which may identify an inflamed or complicated diverticulum, and capsule endoscopy or balloon-assisted enteroscopy for direct visualization. Angiography may be used in cases of active bleeding.

Treatment

The management of an asymptomatic, incidentally discovered Meckel's diverticulum is controversial, with many surgeons advocating for non-operative observation. Surgical resection is definitively indicated in all symptomatic cases. The standard procedure is a segmental ileal resection (diverticulectomy with a wedge of adjacent bowel) followed by primary anastomosis, which ensures removal of any ectopic tissue in the diverticulum or adjacent ileum. This can often be performed laparoscopically. In cases of inflammation or where the base is narrow, simple diverticulectomy may be sufficient. The procedure is typically curative, and outcomes from surgical intervention are generally excellent.

Epidemiology

Meckel's diverticulum has a reported prevalence of approximately 2% in the general population based on autopsy and surgical studies, with a male-to-female ratio of about 2:1 in symptomatic cases. Although present from birth, over half of symptomatic cases present in children under the age of 2 years. The risk of complications decreases with age, with only about 4% of individuals with the anomaly ever developing symptoms. There is no known racial or geographic predilection, and it generally occurs sporadically, though rare familial cases have been reported. It is a common incidental finding during surgeries for other reasons, such as appendectomy or laparoscopy.

Category:Congenital disorders of digestive system Category:Gastroenterology Category:Pediatric surgery