Meckel Diverticulum - Complete Review

Definition and Classification

Embryology and Pathogenesis

Gross Pathology

• Arises from the antimesenteric border of the ileum (vs. enteric duplication cysts, which form on the mesenteric border)
• Length: typically 1-10 cm; "giant" diverticula are those >5 cm
  • Type I giant: long but same caliber as ileum
  • Type II giant (ovoid): larger diameter
• May be connected to the umbilicus or mesentery by a fibrous band

The "Rule of 2s"

Histology / Ectopic Tissue

• Normal mucosa resembles small intestine
• Heterotopic (ectopic) tissue present in ~50% of all diverticula (some series report 27-50%)
• Gastric mucosa = most common ectopic tissue (80-85% of all ectopic tissue in MD); found in 24-70% of symptomatic MD in one meta-analysis
• Pancreatic tissue = second most common; colonic, Brunner glands, biliary, hepatic, jejunal tissue also rarely described
• Presence of ectopic tissue correlates with increased risk of symptomatic/complicated disease
• The ectopic gastric mucosa secretes acid → peptic ulceration of adjacent ileal mucosa ("marginal ulcer" at the gastric-ileal mucosal junction) → bleeding

Epidemiology

• Prevalence: 1.2-4% of the general population (large autopsy series: 2-3%)
• Males are 2-3x more commonly symptomatic than females
• Lifetime risk of complications: ~4-6%
• Risk of complications decreases dramatically with age
• Most adults with MD remain asymptomatic; incidental diagnosis is common

Clinical Presentations and Complications

1. Painless Rectal Bleeding (most common in children)

• Most common complication in pediatric patients, especially infancy to age 5
• Blood is typically maroon/brick-red (even with massive bleeding)
• Rarely BRBPR (like left colon); may present as melena with slower bleeding
• Mechanism: acid from ectopic gastric mucosa → marginal ulcer at gastric-ileal interface
• Despite massive bleeding, death is uncommon in children - hypovolemia causes splanchnic vasoconstriction, reducing blood flow
• H. pylori has been observed in diverticular gastric mucosa but its role in bleeding is considered unlikely

2. Intestinal Obstruction (most common in adults)

• Mechanisms:
  • Intussusception with MD as the lead point (in children >4 years, intussusception is almost always secondary to MD)
  • Volvulus around a persistent fibrous vitelline cord remnant
  • Herniation through a fibrous band
  • Entrapment in an inguinal, femoral, or umbilical hernia = Littre hernia
  • Diverticular lithiasis - an enterolith from the diverticulum migrates into the distal ileum, causing obstruction or provoking inflammation
• Presents with bilious vomiting and abdominal distension
• Volvulus around a vitelline cord can occur in neonates

3. Meckel Diverticulitis

• Acute inflammation of the diverticulum
• Mimics acute appendicitis clinically - diagnosis often made at exploratory laparotomy
• Perforation in ~1/3 of cases (may result from peptic ulceration)
• Chronic form = Meckel ileitis, can mimic Crohn disease of the ileum
• More common in older adults; accounts for up to 20% of complications

4. Neoplasms (rare, mainly adults)

• Carcinoid tumors - most common neoplasm; typically small, resembling jejunoileal carcinoids (not appendiceal) in immunohistochemical characteristics and metastatic potential; patients usually in their 6th decade, often asymptomatic
• Adenocarcinoma - very rare
• Sarcoma - very rare
• Neoplasms do not occur in childhood

Summary by Age Group

Diagnosis

1. Meckel (Technetium-99m Pertechnetate) Scan - Meckel Scan

• Investigation of choice for suspected bleeding MD
• Sensitivity: 80-90%, Specificity: ~95% in children
• 99mTc-pertechnetate is taken up and secreted by gastric mucosa (normal and ectopic); surface mucus cells of stomach and heterotopic gastric tissue in MD concentrate this anion
• Enhancement techniques to improve sensitivity:
  • Cimetidine (H2 blocker): reduces anion secretion from gastric mucosa, increasing intracellular retention and improving visualization
  • Pentagastrin: increases anion uptake (mechanism unclear)
  • Glucagon: reduces peristalsis, decreasing washout artifact
• Limitation: requires ectopic gastric mucosa for a true positive; false-positive and false-negative rates are high in adults
• False positives: Crohn's disease, other inflammatory bowel disorders, intussusception, bowel duplication, urinary tract pathology

2. CT Scan / CT Enterography

• MD appears as a tubular blind-ending structure arising from the antimesenteric border of the terminal ileum
• May be mistaken for a normal bowel loop
• CT enterography improves detection sensitivity significantly
• Useful for diagnosing obstruction or peritonitis, though the diverticulum itself is often difficult to identify

3. Plain Abdominal Radiograph

• Rarely diagnostic
• May show: dilated bowel loops with gas-fluid levels (in obstruction), a saccular soft-tissue shadow in the mid-abdomen (see image below), enterolith (may be indistinguishable from appendicolith)

4. Barium Studies

• Small bowel follow-through: usually not useful - MD may not fill with barium and empties rapidly
• Enteroclysis: better than follow-through; contrast under pressure fills the diverticulum
• Characteristic barium appearance: saccular blind-ending pouch on antimesenteric border with a triradiate fold pattern converging with the ileum
• Useful for chronic persistent symptoms when cross-sectional and nuclear medicine imaging are negative

5. Angiography

• Useful when bleeding is present and Meckel scan is negative
• Localizes source of hemorrhage
• Can demonstrate the vitelline artery (arising from a distal branch of the SMA) and its characteristic blush of tortuous small vessels
• Note: the vitelline artery frequently involutes; the diverticulum is then supplied by branches directly from the SMA

6. Radiolabeled RBC Scan (99mTc-labeled red blood cells)

• Used when Meckel scan is negative and diagnosis is still suspected
• Localizes active bleeding site

7. Capsule Endoscopy

• Small bowel video capsule endoscopy can successfully detect MD
• A 2025 systematic review (PMID: 40202427) catalogued cases discovered by capsule endoscopy

8. Double Balloon Enteroscopy

• Retrograde approach useful for obscure GI bleeding due to MD, particularly when the lesion is close to the ileocecal valve
• Challenging when the lesion is far from the ileocecal valve

9. MR Enterography

• Can be considered to localize the lesion when other modalities are inconclusive, especially for lesions far from the ileocecal valve

10. Ultrasound

• Rarely diagnostic; intussusception caused by MD may be identified on US
• Not a first-line test

Management

Symptomatic / Complicated MD

• Surgical treatment is mandatory for bleeding, obstruction, or perforation
• Diverticulectomy is the standard operation
• Concurrent ileal resection is added if adjacent small bowel is ulcerated, inflamed, obstructed, or if the diverticulum base is wide or involved
• Laparoscopic removal is a well-reported and accepted approach
• Postoperative morbidity occurs in up to 6% of cases

Incidentally Discovered / Asymptomatic MD

• Management is controversial
• Many experts do not recommend prophylactic removal in adults given the low lifetime complication risk (~4-6%)
• Factors favoring resection of asymptomatic MD:
  • Diverticulum >2 cm in length
  • Associated omphalomesenteric band (risk of volvulus/obstruction)
  • Palpable mass within the diverticulum (suggests tumor or ectopic mucosa)
  • Younger male patients
• Some surgeons routinely search for and resect MD during appendectomy or laparotomy for acute abdomen

Littre Hernia

Differential Diagnosis (Pediatric GI Bleeding)

• Red dyes in food/drinks (false hematochezia)
• Bismuth subsalicylate, iron, spinach (false melena)
• Upper GI source with rapid transit (in young children can cause hematochezia)
• Intussusception (other causes)
• Intestinal polyps
• Inflammatory bowel disease (especially if chronic)
• Appendicitis (for pain presentations)

Key Summary Table

• Robbins, Cotran & Kumar Pathologic Basis of Disease
• Sleisenger and Fordtran's Gastrointestinal and Liver Disease
• Yamada's Textbook of Gastroenterology, 7th ed.
• Grainger & Allison's Diagnostic Radiology
• Rosen's Emergency Medicine

Meckel Diverticulum — 10 Marks Answer

Definition

Rule of 2s

Anatomy

• Arises from the antimesenteric border of the ileum
• Contains ectopic tissue in ~50% of cases
• Ectopic gastric mucosa = 80-85% of all ectopic tissue
• Pancreatic tissue = second most common
• Ectopic gastric mucosa secretes acid → peptic ulceration of adjacent ileal mucosa ("marginal ulcer") → bleeding

Complications (Clinical Features)

1. Painless Rectal Bleeding

• Most common complication in children (especially <5 years)
• Blood is typically maroon/brick-red; melena may occur with slower bleeding
• Due to acid secretion by ectopic gastric mucosa → marginal ulceration
• Despite massive bleeding, death is uncommon in children (splanchnic vasoconstriction limits blood loss)

2. Intestinal Obstruction

• Most common complication in adults
• Mechanisms:
  • Intussusception (MD acts as lead point - in children >4 years, nearly all intussusceptions are secondary to MD)
  • Volvulus around a persistent fibrous vitelline cord
  • Littre hernia - MD trapped in an inguinal/femoral/umbilical hernia sac
  • Diverticular lithiasis (enterolith causing obstruction)
• Presents with bilious vomiting and abdominal distension

3. Meckel Diverticulitis

• Acute inflammation mimicking acute appendicitis - diagnosis usually made at laparotomy
• Perforation occurs in ~1/3 of cases
• Chronic form (Meckel ileitis) can mimic Crohn disease
• More common in older adults (~20% of complications)

4. Neoplasms (rare)

• Carcinoid tumor (most common), adenocarcinoma, sarcoma
• Mainly in adults; do not occur in childhood

Investigations

Meckel (Technetium-99m Pertechnetate) Scan — Investigation of Choice

• 99mTc pertechnetate is taken up by ectopic gastric mucosa
• Sensitivity 80-90%, Specificity ~95% in children
• Sensitivity enhanced by:
  • Cimetidine (H2 blocker) - reduces anion secretion, improves retention
  • Pentagastrin - enhances uptake
• Limitation: requires ectopic gastric mucosa; less reliable in adults

Other Investigations

Management

Symptomatic / Complicated MD

• Surgical treatment is the only definitive therapy
• Diverticulectomy - standard operation
• Diverticulectomy + ileal resection - if adjacent bowel is ulcerated, inflamed, or the base is wide
• Laparoscopic approach is well established

Asymptomatic / Incidentally Found MD

• Management is controversial; prophylactic resection is generally not recommended in adults
• Resection favored if:
  • Length >2 cm
  • Associated fibrous omphalomesenteric band (volvulus risk)
  • Palpable mass within the diverticulum
  • Young male patient

Summary