A 24-year-old woman gives birth to a term infant after an uncomplicated pregnancy. Apgar scores are 9 and 10 at 1 and 5 minutes after birth. The infant's length and weight are at the 55th percentile. There is no significant passage of meconium. Three days after birth, the infant vomits all oral feedings. On physical examination, the infant is afebrile, but the abdomen is distended and tender, and bowel sounds are reduced. An abdominal ultrasound scan shows marked colonic dilation above a narrow segment in the distal sigmoid region. A biopsy specimen from the narrowed region shows an absence of ganglion cells in the muscle wall and submucosa. Which of the following is most likely to produce these findings?

In Hirschsprung disease, seen in 1 in 5000 live births, the aganglionic segment (either a short or long segment) of the bowel wall produces a functional obstruction with proximal distention. Most familial cases and some sporadic cases have RET gene mutations affecting neural crest cell migration. Atresia is congenitally narrowed segments of the bowel (usually the small intestine) that occur with other anomalies. Patients with trisomy 21 may have intestinal (usually duodenal) atresia. The complete absence of the colonic lumen at a point of atresia is a rare congenital anomaly and is not associated with the loss of ganglion cells. Intussusception also is a cause of bowel obstruction in infants, but it is not caused by an aganglionic segment of bowel. Necrotizing enterocolitis is a complication of prematurity. A volvulus is a form of mechanical obstruction that occurs from the twisting of the small bowel on the mesentery or twisting of a segment of the colon (sigmoid or cecal regions).