Divertikulum Meckel

01Pathophysiology

Meckel's diverticulum is the most common congenital anomaly of the gastrointestinal tract. It arises from incomplete obliteration of the vitelline duct (also called the omphalomesenteric duct), which normally connects the embryonic midgut to the yolk sac and should fully regress by the seventh week of gestation. When obliteration fails, a blind-ended pouch persists on the antimesenteric border of the ileum, typically located approximately 2 feet (60 cm) proximal to the ileocecal valve.

Because it is a true diverticulum, the wall contains all three histological layers: mucosa, submucosa, and muscularis propria. This distinguishes it from false (or pseudo) diverticula, which lack the muscular layer. The diverticulum is supplied by a persistent vitelline artery, a branch of the superior mesenteric artery.

The clinical significance centers on the presence of ectopic tissue within the diverticulum. Roughly half of all symptomatic Meckel diverticula contain heterotopic mucosa, with gastric mucosa being the most common type, followed by pancreatic tissue. Ectopic gastric mucosa secretes hydrochloric acid, which causes peptic ulceration of the adjacent normal ileal mucosa. This ulceration leads to erosion into submucosal blood vessels, producing painless lower GI bleeding. The bleeding is typically brisk enough to cause brick-red or dark maroon stools, and it is the single most common cause of significant painless lower GI hemorrhage in children under 2 years old.

The classic teaching framework is the "Rule of 2s": 2% of the population is affected, the diverticulum is found within 2 feet of the ileocecal valve, it is approximately 2 inches (5 cm) long, the two most common types of ectopic tissue are gastric and pancreatic, it most often becomes symptomatic before age 2, and symptomatic males outnumber females roughly 2 to 1.

02Classification and Clinical Manifestation

03Diagnostic Workup

The best initial test for a child presenting with painless lower GI bleeding suspicious for Meckel's diverticulum is the Technetium-99m pertechnetate scan. Pertechnetate is preferentially taken up by mucin-secreting cells of gastric mucosa, whether that mucosa sits in the stomach or resides ectopically within a Meckel diverticulum. The scan carries a sensitivity of approximately 85% in pediatric patients but drops considerably in adults, partly because adults are less likely to harbor gastric-type ectopic tissue.

Sensitivity can be augmented pharmacologically. An H2-receptor antagonist (classically cimetidine) is often administered before the scan. The drug blocks acid secretion from the ectopic gastric cells but does not interfere with the cells' ability to take up the radiotracer; this allows the tracer to accumulate rather than being washed away, improving detection. Pentagastrin stimulates tracer uptake directly, while glucagon slows intestinal motility and reduces isotope washout.

If the Meckel scan is negative yet the clinical suspicion remains high, a tagged red blood cell (RBC) scan can detect active bleeding at rates as low as 0.1 mL/min, although it localizes the bleed without confirming the underlying diagnosis. Mesenteric angiography is reserved for patients with brisk hemorrhage and can detect bleeding rates of 0.5 mL/min or greater.

The most accurate (confirmatory) test is surgical exploration with histopathological analysis of the excised tissue. In practice, a child with a convincingly positive Meckel scan and a compatible clinical picture proceeds directly to surgery, making the operation both diagnostic and therapeutic.

For presentations involving obstruction or diverticulitis rather than bleeding, CT imaging becomes the more useful initial study. A blind-ending tubular structure arising from the distal ileum, with or without surrounding fat stranding or signs of bowel obstruction, supports the diagnosis.

04Management and Treatment

Acute stabilization follows standard resuscitation principles. For a child presenting with significant GI hemorrhage, the first step is always hemodynamic stabilization with isotonic crystalloid (normal saline or lactated Ringer's) at 20 mL/kg IV boluses, repeated up to three times. If the child remains hemodynamically unstable or the hemoglobin drops below 7 g/dL, packed red blood cell transfusion (10 to 15 mL/kg) is indicated. Type and crossmatch should be sent early. Coagulopathy, if present, is corrected with fresh frozen plasma or platelets as needed.

Once the patient is stabilized, the definitive treatment is surgical resection. Two approaches exist. A diverticulectomy (simple excision of the diverticulum at its base with primary closure of the ileum) is appropriate when the diverticulum has a narrow base and there is no ulceration of the surrounding ileal mucosa. A segmental ileal resection with primary end-to-end anastomosis is preferred when the base is wide, when there is ulceration or ischemia involving the adjacent bowel wall, or when a tumor is suspected. Both procedures can be performed via laparoscopy or open laparotomy.

For diverticulitis or perforation, broad-spectrum intravenous antibiotics covering gram-negative and anaerobic organisms should be initiated preoperatively (piperacillin-tazobactam or a combination of ceftriaxone plus metronidazole are standard choices) and continued postoperatively for a course guided by the degree of peritoneal contamination, typically 3 to 5 days for uncomplicated cases.

The question of incidentally discovered Meckel diverticulum is a classic exam point. Current consensus leans toward prophylactic resection in younger patients (under 50 years) or when the diverticulum appears abnormal on palpation. In older adults undergoing unrelated surgery, if the diverticulum looks grossly normal, observation without resection is generally acceptable because the lifetime risk of complications decreases with age.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common trap on this topic is confusing Meckel's diverticulum with appendicitis. A vignette describing a child with right lower quadrant pain and a normal appendix at surgery should immediately raise the question: did the surgeon look for a Meckel diverticulum? Test writers use this scenario to check whether you know that the next step after finding a normal appendix in a patient with convincing peritoneal signs is to inspect the terminal ileum for a Meckel diverticulum. Failing to consider this diagnosis in that context is the single most tested pitfall.

A second common error is choosing the wrong diagnostic study. When a young child presents with painless lower GI bleeding, the answer is a Technetium-99m pertechnetate scan, not a colonoscopy and not a barium study. Colonoscopy is the answer for polyps; the Meckel scan is the answer for ectopic gastric mucosa in the ileum.

A third point frequently tested is the distinction between true and false diverticula. Meckel's is a true diverticulum (all bowel wall layers), while colonic diverticula seen in diverticulosis are false diverticula (mucosal and submucosal herniation only). This histological distinction may appear as a direct question or as a distractor.

Finally, remember the Rule of 2s as a rapid-recall framework, but recognize that exam questions will not hand you a patient who neatly fits every "2." The core competency being tested is the ability to recognize painless, significant lower GI bleeding in a child, connect it to ectopic gastric tissue in a congenital ileal outpouching, order the correct nuclear medicine scan, and proceed to surgery.