What is the most likely diagnosis for an abdominal x-ray showing a triple bubble sign in a 12-hour-old infant?

The triple bubble sign observed on an abdominal x-ray in a 12-hour-old infant is most indicative of intestinal atresia. This radiological finding typically consists of three distinct air-filled structures that represent the dilated segments of the proximal stomach and two proximal segments of the small intestine, separated by atresia.

In the case of intestinal atresia, a congenital obstruction occurs in the intestine, leading to the accumulation of air and fluid above the blockage. This results in the characteristic appearance of the triple bubble on imaging, demonstrating the segments affected by the obstruction.

On the other hand, Hirschsprung disease is characterized by the absence of ganglion cells in a portion of the colon, leading to functional obstruction and typically results in a different radiological appearance and clinical presentation. Meconium ileus usually presents with a different pattern, often associated with cystic fibrosis, and typically shows a predisposing pattern of gas in the distal bowel rather than the triple bubble sign. Volvulus involves twisting of the intestine and may present with different radiographic findings, such as an 'apple core' sign, but does not specifically result in the triple bubble appearance. Thus, the presence of a triple bubble sign makes intestinal atresia the most likely diagnosis