Bilious emesis is any green or yellow emesis. The presence of bile in an infant’s vomit is essential diagnostic information because bilious emesis is most likely due to a surgically correctable lesion until proven otherwise. Obstructive processes proximal to the pylorus always cause nonbilious emesis, whereas bilious emesis implies a patent pylorus with obstruction distal to the ampulla of Vater. Distinguishing between proximal and distal causes of obstruction will determine what type of diagnostic study to perform.

Rotational defects are thought to be present in nearly all patients with congenital diaphragmatic hernia and abdominal wall defects such as gastroschisis and omphalocele. In children with these conditions, volvulus is rare due to both the abnormal anatomy and adhesions that develop after surgical repair. Patients with heterotaxy syndrome, or abnormal positioning of intrathoracic or intra-abdominal organs, are likely to have malrotation and should therefore undergo a diagnostic workup. Intestinal atresias, in particular duodenal atresia, are also associated with and perhaps in part caused by malrotation and should therefore be assessed during surgical repair of the atresia. There are some syndromic associations that have been described including Trisomy 21 (Down syndrome).

Given that the patient is hemodynamically stable, the first study to obtain is a plain abdominal radiograph. While plain radiographs are rarely diagnostic, they may exclude gross perforation, which would reveal free air under the diaphragm. If there is evidence of perforation, no additional studies are needed and the patient should be taken to the operating room for urgent laparotomy. The presence and location of bowel gas on plain radiographs may also help determine whether the patient has a proximal (duodenum or proximal jejunum) or distal (ileum or colon) obstruction, which will then guide further workup based on the differential diagnosis (Fig. 32.2).