Meckel Diverticulum

See Small Bowel Diverticular Disease for the true/false diverticula overview — Meckel diverticulum is the most common true congenital diverticulum of the small bowel. Content below is from a textbook reference chapter (Sabiston Ch50 - Diverticular Disease & Miscellaneous Problems), not primary literature.

Incidence and cause

The most commonly encountered congenital anomaly of the small intestine, occurring in about 2% of the population. Initially reported in 1598 by Hildanus, then described in detail by Johann Meckel in 1809. Located on the antimesenteric border of the ileum, 45–60 cm proximal to the ileocecal valve; results from incomplete closure of the omphalomesenteric (vitelline) duct. Equal incidence in men and women. May range from a small bump easily missed to a long projection communicating with the umbilicus by a persistent fibrous cord (Fig. 50.43), or — much less commonly — a patent fistula. The usual manifestation is a relatively wide-mouthed diverticulum ~5 cm long, up to 2 cm diameter (Fig. 50.44).

Cells lining the vitelline duct are pluripotent; it is not uncommon to find heterotopic tissue within the Meckel diverticulum — the most common of which is gastric mucosa (present in 50% of Meckel diverticula). Pancreatic mucosa is encountered in about 5% of diverticula; less commonly, these diverticula may harbor colonic mucosa.

Clinical manifestations

Most Meckel diverticula are benign and incidentally discovered during autopsy, laparotomy, or barium studies (Fig. 50.45). The most common clinical presentation of symptomatic Meckel diverticulum is gastrointestinal bleeding, occurring in 25–50% of patients who present with complications; hemorrhage is the most common symptomatic presentation in children ≤2 years old. May be manifested as acute massive hemorrhage, anemia secondary to chronic bleeding, or a self-limited recurrent episodic event. The usual source of bleeding is a chronic acid-induced ulcer in the ileum adjacent to a Meckel diverticulum containing gastric mucosa.

Another common presenting symptom is intestinal obstruction. May result from a volvulus of the small bowel surrounding the diverticulum and its fibrotic band attached to the abdominal wall, intussusception, or (rarely) incarceration of the diverticulum in an inguinal hernia (Littre hernia). Volvulus is usually acute and, if allowed to progress, may cause strangulation. In intussusception, a broad-based diverticulum invaginates and is carried forward by peristalsis — may be ileoileal or ileocolic, presenting as acute obstruction with urge to defecate, early vomiting, and occasionally passage of the classic currant jelly stool. A palpable mass may be present. Although reduction of an intussusception secondary to Meckel diverticulum can sometimes be performed by barium enema, the patient should still undergo resection of the diverticulum to negate subsequent recurrence.

Diverticulitis accounts for 10–20% of symptomatic presentations, more common in adult patients. Meckel diverticulitis, clinically indistinguishable from appendicitis, should be considered in the differential diagnosis of a patient with RLQ pain. Progression of the diverticulitis may lead to perforation and peritonitis. When the appendix is found to be normal during exploration for suspected appendicitis, the distal ileum should be inspected for an inflamed Meckel diverticulum.

Neoplasms can also occur in a Meckel diverticulum, with NET as the most common malignant neoplasm (77%). Other histologic types include adenocarcinoma (11%, generally originating from the gastric mucosa), GIST (10%), and lymphoma (1%).

Diagnostic studies

Diagnosis may be difficult. Plain abdominal radiography, CT, and ultrasonography are rarely helpful. In children, the single most accurate diagnostic test is sodium 99mTc-pertechnetate scintigraphy, preferentially taken up by mucus-secreting cells of gastric mucosa and ectopic gastric tissue in the diverticulum (Fig. 50.46). Diagnostic sensitivity as high as 85%, specificity 95%, accuracy 90% in the pediatric age group. In adults, sensitivity of the scan falls to 63% because of the smaller presence of gastric mucosa compared with the pediatric age group. Sensitivity/specificity can be improved with pharmacologic agents — cimetidine may increase scintigraphy sensitivity by decreasing peptic secretion without affecting radionuclide uptake (which may be caused by pertechnetate release from the diverticular lumen); cimetidine treatment thus results in higher radionuclide concentrations in the diverticular wall.

False-negative results can occur because of absent gastric mucosal cells, inflammatory changes causing edema/necrosis, presence of outlet obstruction of the diverticulum, or anemia. In false-negative cases, barium contrast imaging, mesenteric arteriography, or double-balloon endoscopy can be helpful. In patients with acute hemorrhage, angiography is sometimes useful. Surgical intervention should not be delayed to obtain imaging for a patient with signs/symptoms of hemorrhage and hemodynamic instability.

Treatment

Treatment of a symptomatic Meckel diverticulum requires prompt surgical intervention with diverticulectomy or segmental resection of ileum containing the diverticulum. Segmental small bowel resection is required for patients with hemorrhage, as the bleeding site is usually adjacent to the diverticulum (not within it). Diverticulectomy for nonbleeding Meckel diverticula can be performed with a hand-sewn technique or stapling across the base of the diverticulum in a diagonal or transverse line to minimize the risk for subsequent stenosis. Retrospective studies show equivalent outcomes in laparoscopic resection compared with open resection.

Incidentally found (asymptomatic) diverticulum: the optimal treatment remains debated. It is generally recommended that asymptomatic diverticula found in children during laparotomy be resected. The treatment of Meckel diverticula found incidentally in adults remains controversial. A landmark paper by Soltero and Bill (studying 202 diseased Meckel diverticula found in King County, Washington, over 15 years) formed the basis of surgical management for many years, estimating the likelihood of an asymptomatic Meckel diverticulum becoming symptomatic in adults at ≤2%, and — given that morbidity rates from incidental removal were 12% at the time — recommended not removing incidental Meckel diverticula. A more recent systematic review by Zani et al. challenged this, identifying a clear increase in morbidity with resection and calculating that, to avoid one death related to the diverticulum, over 700 incidental diverticulum resections would be required — supporting the conservative approach. However, other studies have challenged this more conservative approach in adults with an incidental Meckel diverticulum: a recent population-based study (1973–2006) found the mean annual incidence of malignancy in a Meckel diverticulum was approximately 1.44 per 10 million, identifying an adjusted cancer risk in the Meckel diverticulum ~70 times higher than any other ileal site — identifying it as a “hot spot” for malignant disease in the ileum. Given the increased lifetime risk of malignant transformation, some authors also advocate removal of an incidental Meckel diverticulum. A recent review suggested the decision for resection of an incidentally found diverticulum should be based on the risk of future complications — factors associated with a higher risk of complications, warranting consideration of resection, include age younger than 50, male sex, diverticulum length >2 cm, and ectopic tissue or palpable abnormalities.

Taken together, the decision for surgical resection of an incidentally found Meckel diverticulum needs to be made on a personalized basis weighing the risk and benefits of malignancy, age, and complications — future prospective trials are needed to clarify this controversy.

Open items / gaps

• No primary literature yet in the wiki independently appraising the Soltero and Bill, Zani, or population-based malignancy-incidence studies cited above — currently only the textbook’s narrative summary of each. Given the genuinely unresolved controversy over incidental-finding management, this would be a good candidate for a dedicated primary-literature ingest if Stephen wants to dig deeper.