A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 1-year-old previously healthy male presents to the emergency department with 3 hours of intermittent abdominal pain, vomiting, and one episode of dark red stools. On exam, his abdomen is tender to palpation and there are decreased bowel sounds. A CT scan reveals air fluid levels and a cystic mass in the ileum. Gross specimen histology reveals gastric tissue. What is the cause of this patient's problems?
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A
Obstruction of the lumen of the appendix by a fecalithIncorrect. Appendiceal obstruction by a fecalith causes appendicitis (RLQ pain, fever) — not a cystic ileal mass containing ectopic gastric tissue.
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B
Abnormal closure of the vitilline ductCorrect. Failure of the vitelline (omphalomesenteric) duct to obliterate produces a Meckel diverticulum, which can contain ectopic gastric mucosa that ulcerates and bleeds — matching this toddler with painless GI bleeding and ileal cystic mass.
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C
Twisting of the midgut secondary to malrotationIncorrect. Midgut volvulus from malrotation typically presents in neonates with bilious vomiting and acute bowel ischemia — not a chronic cystic ileal mass with gastric tissue.
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D
Ingestion of contaminated waterIncorrect. Contaminated water ingestion causes infectious diarrhea (Giardia, viral, bacterial), not a structural cystic ileal mass with ectopic mucosa.
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E
Intussusception of the terminal ileum into the cecumIncorrect. Intussusception classically presents in this age range with currant-jelly stools and a sausage-shaped mass, but pathology shows telescoped bowel — not a cystic ileal mass with ectopic gastric mucosa, which is pathognomonic for Meckel diverticulum.
↑ Tap an answer to reveal the reasoning
Answer: B. Intermittent abdominal pain, vomiting, and painless dark/maroon ("currant jelly") bleeding in a toddler, with a cystic ileal mass that contains ectopic gastric mucosa on histology, is the textbook presentation of a Meckel diverticulum. Meckel is a true diverticulum (all 3 layers of bowel wall) — a persistent remnant of the omphalomesenteric (vitelline) duct, which normally obliterates by 7 weeks of gestation.
The rule of 2s: 2% of the population, 2 feet from the ileocecal valve, 2 inches long, presents before age 2, contains 2 tissue types (gastric and/or pancreatic ectopia). Bleeding occurs because acid-secreting ectopic gastric mucosa ulcerates the adjacent ileal mucosa. The diagnosis is made by a 99mTc-pertechnetate (Meckel) scan, which is taken up by gastric mucosa. Treatment is surgical resection.
Appendicitis (fecalith obstruction) presents with periumbilical pain migrating to RLQ — and would not contain gastric tissue. Midgut volvulus from malrotation presents in the first month of life with bilious vomiting and bowel ischemia, not a cystic ileal mass with gastric mucosa. Contaminated water ingestion (giardia, etc.) causes diarrhea, not a cystic mass with ectopic gastric tissue.
**Why each option:**
**A.** Appendiceal obstruction by a fecalith causes appendicitis (RLQ pain, fever) — not a cystic ileal mass containing ectopic gastric tissue.
**B.** Correct. Failure of the vitelline (omphalomesenteric) duct to obliterate produces a Meckel diverticulum, which can contain ectopic gastric mucosa that ulcerates and bleeds — matching this toddler with painless GI bleeding and ileal cystic mass.
**C.** Midgut volvulus from malrotation typically presents in neonates with bilious vomiting and acute bowel ischemia — not a chronic cystic ileal mass with gastric tissue.
**D.** Contaminated water ingestion causes infectious diarrhea (Giardia, viral, bacterial), not a structural cystic ileal mass with ectopic mucosa.