A Meckel diverticulum is an embryologic abnormality that is part of a spectrum of anomalies known as yolk stalk or omphalomesenteric duct remnants (see the images below). Fabricus Hildanus first described a Meckel diverticulum in 1598. In 1809, Johann Meckel, an anatomist, described this anomaly in detail. He identified the origin of the diverticulum as the omphalomesenteric duct and emphasized that this anatomic abnormality was a potential cause of disease. In 1904, Salzer became the first to identify ectopic mucosa within the diverticulum.
Depending on the type of anomaly, patients may be completely asymptomatic or may present with bleeding, inflammation, obstruction, or umbilical drainage. (See Presentation.) Treatment is surgical. (See Treatment.)
The omphalomesenteric (vitelline) duct typically arises from a point about 60 cm proximal to the ileocecal valve in adults. The Meckel diverticulum is an antimesenteric structure but receives its blood supply from the mesentery of the ileum. Thus, a typical feeding vessel (vitelline artery, also described as the omphalomesenteric mesentery) may be identified. It crosses from the mesentery of the ileum, across the intestine itself, and along the length of the diverticulum. This feeding vessel must be individually clipped and divided during a laparoscopic Meckel diverticulectomy.
Meckel diverticula may contain ectopic mucosa. The two most common types of ectopic mucosa are gastric and pancreatic. As many as 50% of all diverticula contain gastric mucosa, whereas 5% contain pancreatic mucosa. Ectopic gastric mucosa results in secretion of acid onto adjacent ileal mucosa, causing ulceration and bleeding.
The pathophysiology varies depending on the etiology of symptoms (see Presentation). A 16-year review of symptomatic Meckel diverticula in children revealed that 55.5% of patients had gastrointestinal (GI) bleeding, 14.2% had intestinal obstruction, 15.8% presented with peritonitis, and 14.2% had umbilical drainage. 
The existence of a Meckel diverticulum or one of its variants is due to simple embryology. The yolk sac of the developing embryo is connected to the primitive gut by the yolk stalk or vitelline (ie, omphalomesenteric) duct. This structure typically regresses between weeks 5 and 7 of fetal life. If this process of regression fails, various anomalies can occur. This spectrum of defects includes a Meckel diverticulum, a fibrous cord attaching the distal ileum to the abdominal wall, an umbilical-intestinal fistula, a mucosa-lined cyst, or an umbilical sinus. Various possible complications are associated with different omphalomesenteric remnants (see the image below).
Meckel diverticula are found in approximately 2% of the population. The prevalence of symptomatic Meckel diverticula is estimated to be 4-35% of the at-risk population, depending on the age group studied. More than 60% of patients who develop symptoms from this anomaly are aged 2 years or younger.
Patients typically do not have further bleeding episodes once the Meckel diverticulum and ectopic gastric mucosa have been excised. Patients who require exploratory laparotomy for bowel obstruction are at risk for adhesive bowel obstruction in the future.