What condition is characterized by bilious vomiting and peritoneal signs in a week-old baby?

The condition characterized by bilious vomiting and peritoneal signs in a week-old baby is intestinal malrotation. This condition occurs when the intestine does not rotate properly during fetal development, leading to an abnormal position of the small intestine and potentially causing obstruction.

In cases of intestinal malrotation, the presence of bilious vomiting indicates that there is a blockage below the level of the duodenum, as bile is typically secreted by the liver and enters the duodenum. The peritoneal signs suggest that there might be irritation or inflammation of the peritoneum, which could occur due to volvulus (twisting of the intestine), leading to ischemia and potential perforation.

Other conditions listed have different presentations. Meconium ileus, often seen in cystic fibrosis, typically manifests with a failure to pass meconium and can lead to abdominal distension but does not usually present with peritoneal signs as prominently in the early stages. Pyloric stenosis, while causing projectile non-bilious vomiting typically occurs later and is associated with a "string sign" but does not emit bilious vomitus due to obstruction being above the duodenum. Duodenal atresia also leads to bilious vomiting but is