Which feature is key for differentiating pyloric stenosis from malrotation in a neonate?

Projectile vomiting is a key feature that helps differentiate pyloric stenosis from malrotation in neonates. Pyloric stenosis is characterized by a hypertrophy of the pylorus, which leads to a narrowing of the pyloric channel and causes severe, non-bilious projectile vomiting after feeding. This type of vomiting occurs because the food cannot pass from the stomach into the duodenum, leading to a forceful expulsion.

In contrast, malrotation typically presents with bilious vomiting and can lead to more acute abdominal symptoms due to intestinal obstruction or volvulus, where the intestines twist around themselves. While malrotation may also cause vomiting, the presence of bile distinguishes it from pyloric stenosis. The projectile nature of the vomiting in pyloric stenosis is a hallmark feature that clinicians look for during evaluation.

Age of the infant, presence of fever, and blood in the stool may provide some context in the clinical picture but are not as definitive in distinguishing between these two conditions as projectile vomiting is.