Pyloric stenosis is a narrowing of the opening of the stomach, known as the pylorus, through which food and other stomach contents enter the small intestine. This narrowing occurs in newborns and must be corrected immediately with surgery so the baby can digest milk and thrive.

What is going on in the body?

The pylorus is a circular muscle. When an infant has pyloric stenosis, the pyloric muscle is enlarged, narrowing the entrance to the small intestine. This enlargement produces a partial obstruction or blockage at the pylorus. Over a period of time, the pylorus becomes inflamed and swollen producing even further obstruction. Although infants are born with pyloric stenosis, symptoms usually are not noticed until 2 or 3 weeks after birth.

What are the causes and risks of the condition?

Pyloric stenosis is a congenital defect, or condition present at birth. The exact cause of this condition is unknown. Pyloric stenosis affects more males than females (about 1 in 750 females and 1 in 150 males). It is the most common condition requiring surgery in the first 2 months of life. There is a 5% chance that a sibling of someone with pyloric stenosis will also have it and about a 25% chance that children of a mother with a history of pyloric stenosis will also have it.