What characterizes the vomiting typically seen in pyloric stenosis?

Non-bilious vomiting is a key characteristic of pyloric stenosis. In this condition, the pylorus, which is the opening from the stomach into the small intestine, becomes narrowed. As a result, food cannot pass through easily, leading to forceful vomiting that occurs shortly after feeding. This vomiting typically contains undigested food and is not mixed with bile, which is produced by the liver and can give vomit a greenish color. Since the obstruction is located above the duodenum, bile is not present in the vomit.

In contrast, bilious vomiting indicates that the obstruction is further downstream, causing the vomit to contain bile, which is not the case in pyloric stenosis. The absence of bile is a strong indicator of this condition. Additionally, while diarrhea might accompany other gastrointestinal issues, it is not a feature of pyloric stenosis, as this condition primarily leads to repeated vomiting rather than changes in bowel movements. Vomiting preceded by fever could suggest an infection or other illness, but it doesn't specifically relate to the characteristic presentation of pyloric stenosis. Thus, the hallmark of this condition is indeed non-bilious vomiting, which is critical for recognition and diagnosis.