Review Question - QID 108653

The most likely diagnosis in this patient is Meckel’s diverticulitis, a condition caused by localized inflammation of a Meckel’s diverticulum. These diverticula are caused by persistence of the vitelline duct, an embryologic structure that connects the midgut lumen to the yolk sac in the first trimester.

Meckel's diverticulum is an outpouching of the intestinal lining and is the most common congenital anomaly of the gastrointestinal tract. It is often located approximately 2 feet proximal to the ileocecal valve in the small intestine. These diverticula arise when the vitelline duct (omphalomesenteric duct) fails to obliterate during the seventh week of embryologic development. Clinically, only 2% of all Meckel's diverticula are symptomatic. In these patients, the diverticula contain ectopic acid-secreting gastric mucosa. The acid from these cells leads to localized inflammation and diverticulitis, which manifests clinically as abdominal pain and bloody stool. Pertechnetate scintography is used to identify the existence of a Meckel's diverticula by identifying areas where ectopic gastric parietal cells selectively take up pertechnetate. A common way to remember important aspects about Meckel's diverticula is the “rule of 2’s”: 2% of the population has Meckel's diverticula, 2% of those are symptomatic, they are often found approximately 2 feet proximal to the ileocecal junction, and they often present in the first 2 years of life.

Incorrect Answers:
Answer 1: The metanephric mesenchyme differentiates into renal structures from the glomerulus to the collecting tubule. It is not associated with the gastrointestinal tract and will not cause bloody stool.

Answer 2: The ductus arteriosus shunts blood flow from the right heart to the systemic circulation in the developing embryo, bypassing the immature fetal lung. A persistent ductus arteriosus can present in children with a continuous machine-like heart murmur, bounding pulses, and lower-extremity cyanosis. It is not associated with the gastrointestinal tract and will not cause bloody stool.

Answer 4: The paramesonephric duct (Mullerian duct) eventually develops into the female internal reproductive organs (uterus, fallopian tubes, and inner vagina). This structure is not associated with bloody stool in young children.

Answer 5: The allantois is a precursor to the urachus, an embryological structure that connects the apex of the bladder to the yolk sac. The adult remnant of the urachus is the median umbilical ligament. A patent urachus may present with urine discharge from the umbilicus.

Bullet Summary:
Meckel's diverticulum arises from the vitelline duct, an embryological structure that connects the midgut lumen to the yolk sac. Meckel's diverticulitis commonly presents with right lower quadrant abdominal pain and bloody stool in a young child.