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Pyloric stenosis, also called infantile hypertrophic pyloric stenosis, is caused by an enlarged pylorus, a muscle that opens and closes to allow food to pass through the stomach into the intestine. When this muscle becomes enlarged, digested food is blocked from emptying out of the stomach. The retained food causes the infant to vomit. There is no known reason for this condition.

Pyloric stenosis is one of the most common conditions requiring surgery in infants. It's found more frequently in boys than girls and usually affects children who were born at full term. It rarely occurs in premature infants. Although not thought to be hereditary, pyloric stenosis occurs more commonly in children of parents who had pyloric stenosis themselves as infants.

Signs & symptoms

The main symptom of pyloric stenosis is vomiting undigested breast milk or formula soon after a feeding. Vomiting usually begins at four weeks of age but can happen as early as two weeks after birth. Once vomiting begins, it becomes more frequent and severe, and is often described as "forceful" or "projectile."

Infants with pyloric stenosis may become fussy. Since they can't keep down food, they are hungry between feedings and don't gain weight normally. If vomiting continues, infants may become ill from dehydration.


The doctor may be able to feel the enlarged pyloric muscle, called an "olive," with an examination of the abdomen. If the pylorus cannot be felt, pyloric stenosis can be diagnosed by an ultrasound study or with a test called an upper gastrointestinal (GI) series, which examines the stomach and small intestine. In a GI series, X-rays are taken after the infant drinks a liquid that appears on the X-rays, called contrast.


Pyloric stenosis does not improve by itself and must be corrected with an operation called a pyloromyotomy. Before the operation, your child will be admitted to the hospital and given intravenous fluids. Feedings will be stopped temporarily and restarted after surgery. A blood sample will be taken to check for dehydration and electrolyte abnormalities. Electrolytes are a measure of the amount of sodium, potassium, carbon dioxide and chloride in the blood, and frequent vomiting can make them abnormal. The surgeon will schedule the operation as soon as your child's electrolyte levels are normal and dehydration is corrected. This may take a day of treatment with intravenous fluids.

Pyloromyotomy used to be done through a horizontal incision that left a scar across the abdomen, but is now performed using a small telescope, two miniature instruments and several pencil tip-sized incisions. The operation usually takes about an hour.

Most infants are discharged from the hospital one to two days after the operation.

UCSF Benioff Children's Hospitals medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your child's doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your child's provider.

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