Background
Meckel diverticulum, also known as Meckel's diverticulum, is the most common congenital abnormality of the small intestine; it is caused by an incomplete obliteration of the vitelline duct (ie, failure of the omphalomesenteric duct to close).[ref74} Although originally described by Fabricius Hildanus in 1598, it is named after Johann Friedrich Meckel, who established its embryonic origin in 1809. [1, 2]
Despite the availability of modern imaging techniques, making the diagnosis is challenging. Although Meckel diverticulum is usually asymptomatic, two types of complications can require clinical attention. One type involves ectopic mucosal tissue and most often leads to gastrointestinal bleeding in younger children. In the second type, an obstruction, inflammation or, rarely, perforation of the bowel is present.
Pathophysiology
As noted earlier, Meckel diverticulum is caused by the failure of the omphalomesenteric duct to completely obliterate (at 5-7 weeks' gestation), followed by one of various complications.
The yolk sac is the first element to be formed within the gestational sac. It is involved in maternal-fetal transfer of nutrients in early gestation during the critical period of organogenesis. Early in embryonic life, the fetal midgut receives its nutrition from the yolk sac via the omphalomesenteric/vitelline duct. The duct then undergoes progressive narrowing and usually disappears by 7 weeks' gestation. When the duct fails to fully obliterate, different types of vitelline duct anomalies appear. Examples of such anomalies include (1) a persistent vitelline duct (appearing as a draining fistula at the umbilicus); (2) a fibrous band that connects the ileum to the inner surface of the umbilicus; (3) a patent vitelline sinus beneath the umbilicus; (4) an obliterated bowel portion; (5) a vitelline duct cyst; and, most commonly (97%) Meckel diverticulum, which is a blind-ending, true diverticulum that contains all of the layers normally found in the ileum. [3] The tip of the diverticulum is free in 75% of cases and is attached to the anterior abdominal wall or another structure in the remainder of cases.
Enterocystomas, umbilical sinuses, and omphaloileal fistulas are among the other congenital anomalies associated with Meckel diverticulum.
The diverticulum is usually supplied by the omphalomesenteric artery (a remnant of the vitelline artery), which arises from the ileal branch of the superior mesenteric artery. The artery typically terminates in the diverticulum; however, it has also been reported to continue up to the abdominal wall in some cases. Rarely, these blood vessels persist in the form of fibrous remnants that run between the Meckel diverticulum and the abdominal wall or small bowel mesentery.
A rare reported case of Meckel diverticulum was associated with other umbilical anomalies: A 4-year-old boy presented with abdominal pain, vomiting, and constipation. [4] Upon surgical exploration, a band arising from a Meckel diverticulum was found, causing obstruction of the terminal ileum. A urachal cyst at the umbilicus was attached to the Meckel diverticulum at one end and to the urinary bladder on the other end through a patent urachus.
Although Meckel diverticulum almost always occurs on the antimesenteric border of the ileum, case reports have described a mesenteric location. As per the "rule of twos," it is usually 2 feet (40-60 cm) proximal to the ileocecal valve, 2 cm wide (and 2 inches [5 cm] long), found in 2% of the population, [5] often presents before age 2 years (or within the first 2 decades of lief), is twice as likely to be symptomatic in boys than girls, and contains ectopic mucosa about half the time (two types: gastric and pancreatic). [2] Meckel diverticulum is typically lined by ileal mucosa, but other tissue types are also found with varying frequency.
The heterotopic mucosa is most commonly gastric in origin. This is important because peptic ulceration of this or adjacent mucosa can lead to painless bleeding, perforation, or both. In one study, heterotropic gastric mucosa was found in 62% of cases, pancreatic tissue was found in 6%, both pancreatic tissue and gastric mucosa were found in 5%, jejunal mucosa was found in 2%, Brunner tissue was found in 2% and both gastric and duodenal mucosa were found in 2%. [3] Rarely, colonic, rectal, endometrial, and hepatobiliary tissues have been noted.
Epidemiology
United States data
The prevalence of Meckel diverticulum is usually noted to be approximately 2% of the population, [2, 5] but published series report a range from 0.2% to 4%. [6] Complications are only seen in about 5% of those with the anomaly. In a retrospective survey of 43 children's hospitals in the United States, 815 children had a Meckel diverticulectomy during a 2-year span. [7] Slightly more than half (60%) were symptomatic, and the remainder were incidental findings in children who had laparotomy for a different reason.
International data
Europe and Asia have reported prevalence figures similar to those found in the United States.
Race-related demographics
A study reviewed the Pediatric Hospital Information System (PHIS) database—which included patients admitted to 44 US children’s hospitals—over a 9-year period (2004-2012) to identify demographics of patients with International Classification of Diseases, Ninth Edition, (ICD-9) diagnoses of Meckel diverticulum and a procedure code for Meckel diverticulectomy. It analyzed data for age, payer, ethnicity, and symptoms and found the ethnic distribution of symptomatic Meckel diverticulum was 63.4% White, 4.7% Black, 16.4% Hispanic, 3.9% Asian, and 11.6% other. [8]
Sex-related demographics
Although no sex-based difference has been reported in studies that evaluated this condition as an incidental finding during operations or autopsies, males are as much as 3-4 times more prone to complications than females. In a large series of cases from 2007 to 2008, Meckel diverticulectomy was 2.3 times more common in boys, and boys accounted for 74% of the primary cases. [7]
Age-related demographics
The classic presentation of Meckel diverticulum in children is considered to be painless rectal bleeding in a toddler younger than 2 years. One large case series found that 53% of affected children had surgery before their fourth birthday. However, the largest group (slightly more than 30%) were younger than 1 year. [7] Although most other pediatric cases occur in patients aged 2-8 years, many continue to present with hematochezia.
Younger children have been reported to usually present with hematochezia, whereas adults present with obstruction. However, the series of 815 pediatric (< 8 y) cases described above found that a primary diverticulectomy was performed more commonly (30%) for obstruction than bleeding (27%), and that a substantial proportion (19%) of these patients had intussusception. [7] About one quarter did not have a clear cut diagnosis.
A 2019 study revealed that in 83 children with defined anatomic lead points resulting in intussusception, the most common etiologies in children younger than 2 years were Meckel diverticulum, duplication cyst, and benign polyps. [9] Meckel diverticulum and intestinal duplication accounted for 81% (38/47) of these cases. The most common causes of secondary intussusception in children older than 2 years were intestinal polyps, including Peutz-Jeghers syndrome and Meckel diverticulum, accounting for 72% (26/36) of the cases. [9]
An earlier literature review of Meckel diverticulum in the neonatal period found that the most common manifestations in this age were bowel obstruction (58.3%) and pneumoperitoneum (33.3%). [10] In addition, in both term and preterm neonates, males were even more frequently affected than females, with a male-to-female ratio of 6.5:1. [10] Other neonatal presentations include perforation, intussusception, segmental ileal dilation, ileal volvulus, and massive hematochezia. [7]
In adults with Meckel diverticulum, obstruction and inflammation are more common presentations than lower gastrointestinal bleeding. Several population-based studies have reported a lower incidence of complications with increasing age, although other studies have not. Therefore, the issue of incidental diverticulectomy in older patients remains controversial.
Prognosis
Morbidity and mortality
The diagnosis of Meckel diverticulum can be quite elusive; therefore, a high index of suspicion is warranted to correctly and expeditiously diagnose this condition. Complicated Meckel diverticulum can lead to significant morbidity and mortality, most often because of a delay in diagnosis. For example, a higher frequency of intestinal infarction has been encountered in patients who present with complete intestinal obstruction. Causes of mortality include strangulation, perforation, and exsanguination because of delay in resuscitation.
Complications of Meckel diverticulum typically fall into the categories of bleeding, obstruction, or inflammation (diverticulitis), which could be related to foreign bodies and or tumors. Once a complication arises and surgery is required, the operative mortality and morbidity rates have both been estimated at 12%. [11] The cumulative long-term risk of postoperative complications in this cohort was found to be 7%. If the Meckel diverticulum is removed as an incidental finding, the risk of mortality and morbidity and long-term complications are much lower (1%, 2%, and 2%, respectively). [11]
Pandove et al described a case of internal herniation and intestinal obstruction due to Meckel diverticulum. [12] This rare presentation resulted from internal herniation of bowel loops into a sac formed by mesentery of Meckel diverticulum and its adhesion band.
As many as 5% of complicated Meckel diverticulum contain malignant tissue.
Neuroendocrine tumors arising from Meckel diverticulum are very rare. A 2015 case report described Cushing syndrome due to ectopic adrenocorticotropic hormone (ACTH) secretion from a Meckel diverticulum. [13] Use of somatostatin analogue scintigraphy allowed localization of the ectopic ACTH tumor source. Pathological analysis of the resected submucosal tumor of Meckel diverticulum confirmed a neuroendocrine tumor with immunohistochemistry that was positive for ACTH. Surgical resection led to complete resolution of symptoms. [13]
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Pediatric Meckel Diverticulum. Anteroposterior view of an abdominal radiograph showing multiple dilated loops of a small bowel with air-fluid levels.
