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Difficulty: EasyPediatric Gastrointestinal Disorders

A 48-hour-old full-term male neonate is evaluated in the nursery because he has not yet passed meconium. The nurses report that the infant has had three episodes of bilious vomiting in the past 12 hours. On physical examination, the infant's abdomen is visibly distended and tympanitic. During a digital rectal examination, there is an explosive release of gas and foul-smelling stool, after which the abdomen becomes notably less distended. Which of the following is the most likely underlying pathophysiology of this patient's presentation?

  1. A
    Failure of the midgut to rotate 270 degrees counterclockwise
  2. Failure of neural crest cell migrationAnswer
  3. C
    Hypertrophy of the gastric outlet musculature
  4. D
    Incomplete obliteration of the omphalomesenteric duct
  5. E
    Invagination of a proximal segment of the intestine into a distal segment

Answer

Failure of neural crest cell migration
The correct answer accurately describes the underlying embryological defect in Hirschsprung disease. The condition arises when neural crest cells fail to migrate caudally into the distal colon. Without these cells, the enteric nervous system (Meissner and Auerbach plexuses) fails to develop in that segment. The affected aganglionic bowel cannot relax, creating a functional obstruction that leads to delayed meconium passage, proximal bowel dilation (distension), and bilious vomiting. The classic 'squirt sign' occurs when a finger is inserted into the rectum, temporarily overcoming the spasm and allowing the built-up stool and gas to explosively exit.

Step-by-Step Solution

1
Identify the patient's key clinical signs and symptoms.
The patient is a 48-hour-old neonate with failure to pass meconium, bilious emesis, abdominal distension, and an explosive expulsion of stool upon digital rectal examination (squirt sign).
Recognizing the classic clinical triad of neonatal bowel obstruction alongside the pathognomonic 'squirt sign' narrows the differential diagnosis to a specific etiology.
2
Correlate the clinical findings with the most likely diagnosis.
The combination of these physical findings and the timeline is highly characteristic of Hirschsprung disease.
The squirt sign occurs because the examining finger mechanically relieves the functional obstruction caused by the rigid, aganglionic distal bowel segment.
3
Determine the underlying pathophysiology of the identified diagnosis.
Hirschsprung disease is caused by the failure of neural crest cells to migrate completely into the distal colon during fetal development.
This developmental failure results in an aganglionic segment that lacks both the submucosal (Meissner) and myenteric (Auerbach) plexuses, preventing proper bowel relaxation and resulting in a functional obstruction.

Key Concept

Hirschsprung disease classically presents in neonates with failure to pass meconium, abdominal distension, bilious emesis, and an explosive release of stool on rectal exam ('squirt sign') due to an aganglionic segment of the distal colon caused by the failure of neural crest cell migration.
Estimated Time:1m 0s
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Topics

Pediatric Gastrointestinal Disorders

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