Pyloric stenosis describes a condition in newborn babies. Specifically, pyloric stenosis occurs when the muscle (pyloric muscle or pylorus) that allows food to move from the stomach into the small intestines enlarges. Enlargement of this muscle prevents food from moving easily from the stomach into the small intestine.
A baby with pyloric stenosis experiences gradually increased vomiting, which may eventually become projectile and lead to dehydration. Since the food the baby eats does not enter the small intestines there may not be enough nourishment for the developing infant.
Although the condition affects both boys and girls, boys are 4 times more likely to have this problem. The condition often begins around the second or third week of life but may start any time up to the age of 6 months. Frequent spitting up after feedings is the first clue to the condition. Later, spitting up develops into projectile vomiting: vomiting that is sudden and vigorous, and projects several feet away from the body.