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Pyloric Stenosis

Pyloric stenosis is the most common disorder causing vomiting in infancy which requires surgery.

View a video of a laproscopic pyloromyotomy.



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. This enlarged muscle blocks the passage of food from the stomach through the pylorus into the downstream intestine. After the operation, the pyloric muscle becomes completely normal. Approximately seven percent of infants with pyloric stenosis are born with other medical problems.


The most typical symptom is the forceful vomiting of formula or milk. Symptoms usually begin when children are between three and five weeks old. Some babies may even have small amounts of vomiting before two weeks of age. Eventually the children vomit almost all feeds. Even after vomiting the children stay hungry. Although not letting the baby eat or drink for a short time may let the infant then hold down some clear liquids, the vomiting returns when milk or formula feedings are resumed. Infants who have symptoms for more than a few days often lose weight and becoming dehydrated. Repeated vomiting that persists for several days may irritate the stomach and lead to mild stomach bleeding.


Figure 1: Ultrasound images showing the oval-shaped, enlarged pyloric muscle in a 5-week-old infant. The pyloric muscle length (X-X) is 18 mm and the pyloric muscle thickness (+-+) is 5.2 mm. Lengths greater than 14mm and thicknesses greater than 3 to 4 mm are considered to have pyloric stenosis. (courtesy of Dorothy Bulas, MD.)



After feeding, waves of stomach contractions can sometimes be seen on the abdomen in infants with pyloric stenosis. Your child's doctor may be able to feel the thickened pyloric muscle (called an "olive") when examining the abdomen.

Pyloric stenosis may be confused with other causes of vomiting in infants. Overfeeding is the most common. Often there is a history of formula changes because of intolerance to the current formula. Improved feeding technique, frequent burping, and time are all that is needed for most of these problems to resolve. Vomiting can also be caused by pyloric muscle spasm, gastroesophageal reflux, and rarely, other problems which may require surgery (malrotation of the intestines and other types of intestinal blockage). Vomiting may also be associated with severe medical conditions including infections.

An abdominal ultrasound is used on infants when the pyloric “olive” cannot be felt. The ultrasound can determine if the pyloric muscle is too large (Figure 1). A barium upper gastrointestinal (UGI) series is an x-ray test used if the ultrasound is unclear. The UGI series will show a blocked stomach with a long and narrowed pyloric opening—the “string sign” (Figure 2).

If an UGI series is needed, a tube might need to be placed down into your child’s stomach to remove the barium to decrease the risk of vomiting when they are put asleep for surgery.

Figure 2: Upper gastrointestinal study from a 6-week-old infant shows narrowing of the pyloric channel and the “string sign” in the pylorus.


Repeated vomiting can cause an abnormality in blood tests. Abnormal blood chemistries will need to be fixed with extra fluid by vein prior to surgery. Jaundice, or a yellow skin tone, occurs in approximately 2% of infants with pyloric stenosis and improves by itself after surgery.


Before surgery, care is aimed at replacing the fluids lost from vomiting by giving fluids by vein. Most infants with pyloric stenosis can then be operated on within a day after admission to the hospital. Most of the time the infants are not fed before surgery because of concerns about accidental vomiting during surgery.

Figure 3: Operative technique for pyloromyotomy with optional V-shaped extension of the incision. Note the spreader used to separate just the muscle while leaving the inside lining intact.

A pyloromyotomy, performed while your baby is asleep under general anesthesia, is universally accepted as the preferred operation. The procedure can be done through a variety of incisions. The most frequently used are 1) the right upper abdomen, 2) around the belly button, or 3) using laparoscopy with three very small incisions. Regardless of the approach used, the thickened pyloric muscle around the outside of the pylorus is cut to relieve the blockage while the inside lining of the pylorus is left intact. (Figures 3 and 4).

After the operation, fluids by vein are continued until the infant can take all of their normal feedings by mouth. If the baby is fully awake from anesthesia, feedings can usually be started 4 hours after surgery. The amount and concentration of feedings may be gradually increased until full feeds are reached. Shortly after surgery it is common to see small amounts of vomiting until the baby’s stomach has completely recovered from the procedure. Most infants should go home from the hospital within one or two days after surgery. The results of pyloromyotomy have been excellent and there is no increased risk of stomach or intestinal problems later in life.

Figure 4: Intraoperative picture of the pylorus before and after the muscle has been divided. Note that the inside lining of the pylorus is left intact after the muscle is divided.


Potential complications include bleeding, wound problems like infection and hernias, incomplete cutting of the pyloric muscle leading to a return of symptoms and, extremely rarely, developing a leak in the intestine. The chance of dying from an operation for pyloric stenosis is less than four in one thousand. These very rare deaths are usually related to other severe medical conditions.

Article and graphics adapted from O'Neill: Principles of Pediatric Surgery. © 2003, Elsevier.