Meckel's diverticulum
Executive Summary
Meckel's diverticulum is the most common congenital anomaly of the gastrointestinal tract, arising from the incomplete obliteration of the vitelline (omphalomesenteric) duct during embryonic development. While present in approximately 2% of the population, it remains clinically silent in the majority of cases. Only 4% to 6% of individuals with the anomaly will develop symptoms over their lifetime. The classic description is summarized by the "Rule of Twos": occurring in 2% of the population, with a 2:1 male-to-female ratio, located approximately two feet from the ileocecal valve, and measuring about two inches in length. Complications, when they occur, typically manifest before the age of two.
The primary clinical presentations are gastrointestinal bleeding and acute abdominal symptoms. Bleeding, the most common complication in children, is typically painless and results from acid secretion by ectopic gastric mucosa within the diverticulum, leading to ulceration of the adjacent small bowel. Abdominal symptoms, more common in adults, include bowel obstruction (due to volvulus or intussusception), diverticulitis, and perforation.
Diagnosis is guided by clinical presentation. A Meckel's scan (technetium-99m pertechnetate scintigraphy) is the primary diagnostic tool for identifying ectopic gastric mucosa in patients with gastrointestinal bleeding. For patients presenting with abdominal pain or obstruction, a contrast-enhanced abdominopelvic CT scan is the preferred imaging modality.
Treatment for symptomatic patients is surgical resection. The management of asymptomatic, incidentally discovered Meckel's diverticula is more selective and is based on a risk assessment. Resection is generally recommended for children and for adults under 50 who possess risk factors for future complications, such as male sex, a diverticulum longer than 2 cm, or the presence of palpable abnormal tissue. For adults aged 50 and over without palpable abnormalities, observation is typically favored due to the increased risks of surgery in this population.
1.0 Overview and Embryology
Meckel's diverticulum is a true diverticulum of the small intestine, meaning its wall contains all layers of the normal bowel. It represents a persistent remnant of the omphalomesenteric duct, which connects the embryonic midgut to the yolk sac.
Embryonic Origin: The omphalomesenteric duct typically involutes between the fifth and sixth weeks of gestation as the bowel settles into its final position within the abdominal cavity.
Formation: Incomplete obliteration of this duct leads to the formation of Meckel's diverticulum. It arises from the antimesenteric surface of the middle-to-distal ileum.
Anatomic Variations: The persistence of the duct can result in several anomalies, including omphalomesenteric fistulas (connecting the umbilicus and diverticulum), fibrous bands, and the diverticulum itself.
Vascular Supply: The diverticulum is supplied by the vitelline artery, a branch of the superior mesenteric artery.
Ectopic Tissue: A significant feature is the frequent presence of ectopic tissue within the diverticulum's walls, the embryological origin of which is not fully understood.
2.0 Epidemiology and the "Rule of Twos"
Meckel's diverticulum is the most frequently encountered congenital malformation of the gastrointestinal tract. While there is no clear familial predisposition, its prevalence is noted to be higher in children with other major congenital anomalies.
Prevalence: Studies show a wide range of prevalence, with estimates in the general population from 0.3% to 2.9%. A systematic review of over 31,000 autopsies found a prevalence of 1.2%.
The "Rule of Twos": This classic mnemonic provides a useful summary of the key features:
Occurs in approximately 2 percent of the population.
Exhibits a 2:1 male-to-female ratio.
Is located within 2 feet of the ileocecal valve.
Measures approximately 2 inches in length.
Approximately 2 to 4 percent of patients develop a complication over their lifetime.
Complications often manifest before the age of 2.
Ectopic Tissue Prevalence: Case series indicate that between 12% and 44% of patients with Meckel's diverticula have ectopic tissue within them. The most common types are gastric and pancreatic mucosa. Gastric heterotopia is more common in symptomatic patients (43%) than in asymptomatic patients (12%).
3.0 Clinical Manifestations
Although most individuals with Meckel's diverticulum remain asymptomatic, a small percentage (4-6%) develop complications. Between 25% and 50% of all symptomatic patients are less than 10 years of age.
3.1 Gastrointestinal Bleeding
Bleeding is the most common presentation, particularly in children.
Mechanism: It is caused by ectopic gastric mucosa within the diverticulum secreting acid. This acid leads to ulceration of the adjacent, non-acid-resistant small bowel mucosa, not the diverticulum itself.
Presentation: Patients typically present with painless bleeding. Children often have dark red or maroon stools, while adults may present with melena, reflecting slower colonic transit time. The bleeding can be brisk and may lead to profound anemia.
3.2 Abdominal Symptoms
Gastrointestinal and abdominal symptoms arise from complications such as obstruction, inflammation, or perforation.
Bowel Obstruction: This is a common presentation, particularly in adults. Mechanisms include:
Intussusception: The diverticulum acts as a lead point.
Volvulus: Twisting of the bowel around a fibrous band connecting the diverticulum to the umbilicus.
Herniation: Incarceration of the diverticulum (Littre's hernia).
Inflammation and Perforation (Diverticulitis): Acute inflammation is thought to be caused by obstruction of the diverticular opening. Perforation can lead to peritonitis. Physical findings like abdominal tenderness can vary and are often not specific, sometimes mimicking appendicitis.
4.0 Risk Factors for Symptomatic Disease
While the lifetime risk of developing symptoms is low (estimated between 4.2% and 6.4%), certain clinical features are associated with an increased likelihood of complications. These factors are critical in deciding the management of an incidentally found diverticulum.
Age < 50 years: Odds Ratio [OR] 3.5 (95% CI 2.6-4.8)
Male sex: OR 1.8 (95% CI 1.3-2.4)
Diverticulum length > 2 cm: OR 2.2 (95% CI 1.1-4.4)
Presence of histologically abnormal tissue: OR 13.9 (95% CI 9.9-19.6)
The cumulative effect of these factors is significant. The proportion of patients with symptomatic Meckel's diverticulum increases from 17% when only one criterion is met to 42% with two, and 70% with three or four criteria.
5.0 Diagnosis and Evaluation
A definitive diagnosis is generally made through imaging studies or during surgical exploration, as clinical manifestations are nonspecific.
5.1 When to Suspect Meckel's Diverticulum
Children: Particularly those under 10 years old with painless lower gastrointestinal bleeding.
Adults: Especially those under 40 with gastrointestinal bleeding where standard upper and lower endoscopy have not identified a source.
All Ages: Patients with recurrent or atypical intussusception, or those with symptoms of acute appendicitis after their appendix has already been removed.
5.2 Diagnostic Modalities
6.0 Treatment and Management Strategy
The management approach depends entirely on whether the patient is symptomatic or if the diverticulum was found incidentally.
6.1 Symptomatic Patients
Patients presenting with complications such as bleeding, obstruction, or diverticulitis require surgical resection of the Meckel's diverticulum.
Surgical Techniques:
Simple Diverticulectomy: Removal of the diverticulum, often with a linear gastrointestinal stapler.
Segmental Resection: Removal of the segment of the small bowel containing the diverticulum, followed by primary anastomosis. This is often preferred in cases of bleeding (to remove the adjacent ulcerated bowel), inflammation, a broad-based diverticulum, or palpable abnormalities.
6.2 Asymptomatic (Incidental) Patients
The management of an incidentally found Meckel's diverticulum is controversial and is based on balancing the lifetime risk of complications against the risks of surgery. The following approach is suggested:
7.0 Complications and Prognosis
7.1 Tumors
While rare, tumors can develop within a Meckel's diverticulum. The majority are benign (lipomas, leiomyomas). However, malignant tumors such as adenocarcinoma, carcinoid, and sarcoma have been reported. The adjusted risk of cancer in a Meckel's diverticulum is estimated to be at least 70 times higher than in any other site of the ileum.
7.2 Perioperative Morbidity and Mortality
The risks associated with surgical resection are generally low but are significantly higher for emergency surgery on a symptomatic diverticulum compared to an elective resection.
Mortality: Death related specifically to Meckel's resection is rare, with an estimated incidence of 0.001%.
Complication Rates:
Symptomatic Resection: The perioperative morbidity was 12% in a systematic review.
Elective (Asymptomatic) Resection: The complication rate is approximately 2%.
Common Complications: The most common complications are surgical site infection, postoperative ileus, and anastomotic leak.
