A 2-day-old girl in the newborn nursery is being evaluated for abdominal distension. The patient was born at 39 weeks gestation to a 38-year-old woman by spontaneous vaginal delivery. The mother received epidural analgesia with fentanyl for labor contractions, and the delivery was uncomplicated. Since birth, the girl has shown little interest in breast or bottle feeding. She spit up the last feed but has not vomited. The patient has not yet passed meconium. On physical examination, the anterior fontanelle is open and flat. The palate is intact, and the neck is supple. Cardiopulmonary examination is unremarkable. The abdomen is firm and distended. Examination of the back shows a shallow, 2-mm diameter sacral dimple, and the overlying skin is intact without rashes or hair. Digital rectal examination reveals increased tone followed by release of stool. Extremities appear normal with equal strength and reflexes bilaterally. Abdominal x-ray is shown in the image below:
Show Explanatory Sources
Which of the following is the most likely mechanism for this patient's findings?
Delayed passage of meconium | ||
Hirschsprung disease | Meconium ileus | |
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*Expulsion of gas/stool on rectal examination. | ||
Hirschsprung disease (congenital aganglionic megacolon) should be suspected in neonates with delayed passage of meconium because virtually all full-term infants pass stool within 48 hours of birth. The disorder results from failed neural crest cell migration during fetal development of the enteric nervous system. The affected intestinal segment, most commonly the rectosigmoid colon, lacks innervation and the ability to relax and therefore remains chronically contracted. Although usually an isolated defect, HD is also strongly associated with Down syndrome.
Newborns present with poor feeding, abdominal distension, failure to pass meconium, and bilious emesis. Rectal examination shows increased tone and can produce an explosive expulsion of gas and stool ("squirt sign") from temporary relief from the obstruction.
This patient has x-ray findings of complete bowel obstruction (eg, dilated bowel loops, absent rectal air) without perforation (eg, free air under the diaphragm). Contrast enema in HD shows a transition zone between the narrowed aganglionic segment and the normally innervated, dilated colon (megacolon). Absent ganglion cells on rectal suction biopsy is diagnostic, and treatment is surgical resection of the aganglionic segment.
(Choice B) Intestinal malrotation, or incomplete bowel rotation during embryogenesis, can present with signs of bowel obstruction but is not associated with increased rectal tone or positive "squirt sign."
(Choice C) Some maternal analgesic drugs (eg, opiates) can result in ileus and delayed passage of meconium in the neonate. However, increased rectal tone and marked abdominal distension make this etiology less likely.
(Choice D) Meconium ileus, which may be the earliest manifestation of cystic fibrosis, should also be considered in a neonate with delayed meconium passage. Abnormal chloride transport results in thick, inspissated meconium that impacts in the ileum, causing a narrow, underused colon (microcolon). In contrast to Hirschsprung disease, rectal examination reveals normal tone and would not relieve stool impaction.
(Choice E) Spina bifida occulta, caused by abnormal neural tube closure, can cause neurogenic bowel dysfunction, but other neurologic abnormalities (eg, weakness) would be expected in such cases. In addition, unlike dermatologic findings in spina bifida (eg, hair tuft), this patient's shallow sacral dimple is normal.
Educational objective:
Hirschsprung disease is due to failure of neural crest cell migration and presents with failure to pass meconium within 48 hours after birth. Characteristic findings include complete bowel obstruction (eg, abdominal distension, absent rectal air) and increased tone with release of stool on rectal examination.