A 4-year-old girl is brought to the office after her parents noticed dark red blood on her toilet tissue after a bowel movement. She has had no abdominal pain, dysuria, or discomfort with defecation. The girl has no known medical conditions and takes no medications. Temperature is 36.7 C (98.1 F), blood pressure is 100/40 mm Hg, and pulse is 112/min. Examination shows a soft and nontender abdomen, and bowel sounds are present. Hemoglobin is 8 g/dL, and platelet count is 215,000/mm³. Coagulation studies are normal. Sequential imaging using ^99mTc-pertechnetate scintigraphy demonstrates focal radiotracer accumulation in the right lower quadrant. Which of the following embryologic processes most likely resulted in this patient's condition?

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Quizplus · Accepted Answer

11ec160b_3744_58e7_9249_47045844389e_MD0001_00 This patient with painless rectal bleeding has imaging findings consistent with a Meckel diverticulum, a congenital intestinal abnormality that results from failed obliteration of the vitelline (omphalomesenteric) duct. The vitelline duct is an embryologic remnant that connects the yolk sac to the primitive midgut, and duct closure normally occurs in early gestation. Incomplete closure results in an ileal outpouching with a fibrous connection to the umbilicus. Meckel diverticulum often contains heterotopic gastric mucosa. Secretion of hydrochloric acid by gastric parietal cells causes ulceration and bleeding of local small bowel, resulting in typical findings of painless lower gastrointestinal (GI) bleeding and anemia, as seen in this patient. Less commonly, Meckel diverticulum can present with acute abdominal pain; for example, it can serve as a lead point for intussusception, causing colicky pain and currant jelly stools. Although presentation of Meckel diverticulum is most common at age <2, it can occur at any age. Diagnosis is made with ^99mTc-pertechnetate scan (ie, Meckel scan). The radioisotope ^99mTc-pertechnetate has an affinity for parietal cells of gastric mucosa, and increased uptake of the tracer in the periumbilical/right lower quadrant area is characteristic. (Choice A) The hindgut, supplied by the inferior mesenteric artery, gives rise to the distal colon, rectum, and upper part of the anal canal. Arrest of hindgut descent in utero leads to an imperforate anus, which presents in neonates with failure to pass stool, not painless rectal bleeding. (Choices B and C) Failure of craniocaudal neural crest cell migration results in an aganglionic sigmoid colon/rectum that is narrow and inactive (ie, Hirschsprung disease), and disrupted vascular flow to the ileum results in ileal atresia. Both conditions typically manifest with signs of obstruction (eg, abdominal distension, bilious emesis, failure to pass meconium) in a neonate, not painless GI bleeding in a 4-year-old. (Choice E) Abnormal midgut rotation around the superior mesenteric artery describes intestinal malrotation. Patients may have hematochezia because the narrow mesenteric base seen in malrotation permits the small bowel to twist with subsequent ischemia (ie, volvulus). However, abdominal pain, vomiting, and signs of peritonitis are also typically present. Moreover, ^99mTc-pertechnetate scintigraphy would not show abnormal uptake. Educational objective: Meckel diverticulum results from incomplete obliteration of the vitelline duct and usually presents with painless lower gastrointestinal bleeding. ^99mTc-pertechnetate localizes to heterotopic gastric mucosa that is often contained within a Meckel diverticulum, and uptake in the periumbilical area or right lower quadrant is diagnostic.

A 4-Year-Old Girl Is Brought to the Office After Her