Pyloric stenosis is the narrowing of part of the stomach (the pylorus) that leads into the small intestines. The true cause of pyloric stenosis is unknown. It is believed to begin as the overworked muscle around the outside of the pyloric opening at the bottom of the stomach grows too thick. Males are more commonly affected than females, and there is a genetic predisposition for the disease. Most babies with pyloric stenosis begin to vomit during the second to third week of life. Babies begin with "spitting up" that turns into forceful projectile vomiting. When an infant has pyloric stenosis, the muscles in the pylorus have become enlarged to the point where food is prevented from emptying out of the stomach. It is uncertain whether there is a real congenital narrowing or whether there is a functional hypertrophy of the muscle which develops in the first few weeks of life. Pyloric stenosis is an uncommon condition that affects the pylorus, the opening at the lower end of the stomach that connects the stomach and small intestine. Pyloric stenosis can run in families.
Pyloric stenosis is the second most common problem requiring surgery in newborns. The condition is usually diagnosed by the time a child is 6 months old. Also called infantile hypertrophic pyloric stenosis or gastric outlet obstruction , pyloric stenosis is fairly common - it affects about three out of 1,000 babies in the United States. After the operation, the pyloric muscle becomes completely normal. Approximately seven percent of infants with pyloric stenosis are born with other medical problems. A narrowed or blocked outlet from the stomach (pyloric stenosis) can lead to a serious illness unless it is treated. The pylorus is the connection between the stomach and the first part of the small intestine (duodenum). At first, pyloric stenosis may mimic gastroesophageal reflux, milk allergy, or normal baby spitting, but the vomiting becomes progressively more forceful. It is more common in some medical syndromes, such as Turner syndrome and Cornelia de Lange syndrome.