A 2-day-old boy is evaluated in the newborn nursery due to vomiting. He was born at term to a 30-year-old primigravida via spontaneous vaginal delivery. The patient initially tolerated formula after birth. However, the past 2 feeding attempts resulted in bilious emesis. Cardiopulmonary examination is unremarkable. Abdominal examination shows distension with active bowel sounds. There is no hepatosplenomegaly. Digital rectal examination results in a forceful expulsion of gas. Which of the following processes was most likely impaired during embryologic development of this patient's gastrointestinal system?
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This newborn with bilious emesis and abdominal distension has a rectal examination consistent with Hirschsprung disease (HD). During normal embryogenesis, neural crest cells migrate craniocaudally and provide parasympathetic innervation to the bowel. HD is a congenital disorder caused by failure of neural crest cell migration. The affected distal colon segment, usually confined to the rectosigmoid region, lacks innervation by ganglion cells (derived from neural crest cells) and is therefore unable to relax.
The contracted rectosigmoid colon prevents passage of gas and stool, and affected patients commonly do not pass meconium by 48 hours of life. Newborns with HD may also show signs of distal intestinal obstruction, as in this patient with poor feeding, bilious emesis, and abdominal distension. Increased rectal tone is typical, and forceful expulsion of gas and/or stool ("squirt sign") may occur with digital rectal examination due to temporary relief of the impaction.
Supportive radiographic findings of HD on contrast enema include an abrupt transition zone between the narrow aganglionic segment and the dilated proximal colon (ie, megacolon) due to stool retention. The absence of ganglia on rectal suction biopsy confirms the diagnosis.
(Choices B and E) Meckel diverticulum, which is caused by lack of physiologic obliteration of the vitelline duct, usually presents with painless rectal bleeding; less commonly, signs of bowel obstruction can occur (eg, due to intussusception). Congenital vascular malformations (eg, hemangioma) affecting the gastrointestinal tract would also cause recurrent rectal bleeding. Both conditions rarely present in the newborn period, and neither causes an abnormal rectal examination.
(Choices C and D) Failure of physiologic bowel recanalization causes duodenal atresia, which typically presents in newborns with bilious emesis after feeding due to proximal bowel obstruction. Patients with intestinal malrotation may also exhibit signs of bowel obstruction. However, rectal examination would not produce forceful expulsion of gas in either condition.
Educational objective:
Hirschsprung disease is a congenital disorder caused by failure of normal craniocaudal migration of neural crest cells during embryogenesis. The affected colon segment (eg, rectosigmoid) lacks ganglionic innervation and is unable to relax, resulting in obstruction with failure to pass meconium and bilious emesis. Forceful expulsion of gas and stool on rectal examination is typical.