One of the following will always present with Bilious vomiting -
The CBD opens into the 2nd part of duodenum. So obstructions which are proximal to it like pyloric stenosis & esophageal atresia would not have bile in their associated vomits.
Bilious vomiting would only occur if the obstruction is distal to CBD opening.
Atresia of the 3rd part of duodenum would always produce bilious vomiting.
Malrotation of the gut is a broad entity and may manifest clinically in several different ways. The vomiting may be bilious or nonbilious.
Pyloric stenosis
Esophageal atresia
Atresia of the 3rd part of the duodenum
Malrotation of the gut