MCQ Anatomy Answer 50

The correct answer is B.

Explanation:

The baby boy has Hirschsprung's disease (more common in males), a diagnosis that should spring to mind in an infant who fails to pass meconium soon after birth and presents with chronic constipation. Diagnosis is made most easily and most reliably by anal manometry and/or rectal biopsy. On manometry, internal anal sphincter pressure increases upon rectal balloon distention in patients with Hirschsprung's disease (normally, pressure decreases with distention). Rectal biopsy reveals an absence of ganglion cells (which are derived from neural crest cells) in a portion of the colonic wall. Barium enema would show a transition zone between the aganglionic area of bowel (narrow) and the region of normal bowel proximal to it (dilated).

Defective recanalization of the colon (choice A) results in rectal atresia. In this condition, there is no communication between the rectum and anal canal. Therefore, neither meconium nor stool can be passed.

Herniation of abdominal contents into the umbilical cord (choice C) describes a congenital omphalocele. This occurs due to the failure of all or part of the intestines to return into the abdominal cavity during the tenth week of gestation.

Persistence of the proximal end of the yolk stalk (choice D) results in Meckel's diverticulum, an ileal outpouching that is more prevalent in males. It usually contains ectopic gastric mucosa, which can cause ulceration and bleeding. Inflammation of the diverticulum may produce symptoms and signs similar to appendicitis.

The presence of a rectourinary fistula (choice E) would result in the passage of meconium, stool, and gas into the urine, a diagnostic finding.

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