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Digestive System

Pyloric Stenosis

Lea este articulo en EspanolWhile you were anticipating your new baby, you probably mentally prepared yourself for the messier aspects of child rearing: poopy diapers, food stains, and of course, spit up. But what’s normal and what’s not when it comes to spitting up or vomiting in infants?

About Pyloric Stenosis

Pyloric stenosis, a condition that may affect the gastrointestinal tract during infancy, isn’t normal — it can cause your baby to vomit forcefully and often and may cause other problems such as dehydration and salt and fluid imbalances. Immediate treatment for pyloric stenosis is extremely important.

Pyloric stenosis is a narrowing of the pylorus, the lower part of the stomach through which food and other stomach contents pass to enter the small intestine. When an infant has pyloric stenosis, the muscles in the pylorus have become enlarged and cause narrowing within the pyloric channel to the point where food is prevented from emptying out of the stomach.

Also called infantile hypertrophic pyloric stenosis, pyloric stenosis is a form of gastric outlet obstruction, which means a blockage from the stomach to the intestines. Pyloric stenosis is fairly common — it affects about 3 out of 1,000 babies in the United States. It’s about four times more likely to occur in firstborn male infants and also has been shown to run in families — if a parent had pyloric stenosis, then an infant has up to a 20% risk of developing it. Pyloric stenosis occurs more commonly in Caucasian infants than in babies of other ethnic backgrounds.

Most infants who develop symptoms of pyloric stenosis are usually between 3 to 5 weeks. It is one of the more common causes of intestinal obstruction during infancy that requires surgery.


It is believed that babies who develop pyloric stenosis are not born with it, but that the progressive thickening of the pylorus occurs after birth. A baby will start to show symptoms when the pylorus is so thickened that the stomach can no longer empty properly.

It is not known exactly what causes the thickening of the muscles of the pylorus. It may be a combination of several factors; for example, the use of erythromycin in the first 2 weeks of life has been associated with pyloric stenosis, and there is also a connection in babies whose mothers took this antibiotic at the end of pregnancy or during breastfeeding.

Signs and Symptoms

Symptoms of pyloric stenosis generally begin around 3 weeks of age. They include:

  • Vomiting. The first symptom of pyloric stenosis is usually vomiting. At first it may seem that the baby is simply spitting up frequently, but then it tends to progress to projectile vomiting, in which the breast milk or formula is ejected forcefully from the mouth, in an arc, sometimes over a distance of several feet. Projectile vomiting usually takes place soon after the end of a feeding, although in some cases it may be delayed for hours.

    In some cases, the vomited milk may smell curdled because it has mixed with stomach acid. The vomit will not contain bile, a greenish fluid from the liver that mixes with digested food after it leaves the stomach.

    Despite vomiting, a baby with pyloric stenosis is usually hungry again soon after vomiting and will want to eat. The symptoms of pyloric stenosis can be deceptive because even though a baby may seem uncomfortable, he may not appear to be in great pain or at first look very ill.

  • Changes in stools. Babies with pyloric stenosis usually have fewer, smaller stools because little or no food is reaching the intestines. Constipation or stools that have mucus in them may also be symptoms.
  • Failure to gain weight and lethargy. Most babies with pyloric stenosis will fail to gain weight or will lose weight. As the condition worsens, they are at risk for developing fluid and salt abnormalities and becoming dehydrated.

    Dehydrated infants are less active than usual, and they may develop a sunken “soft spot” on their heads, sunken eyes, and their skin may appear wrinkled. Because less urine is made it may be more than 4 to 6 hours between wet diapers.

    After feeds, increased stomach contractions may make noticeable ripples, or waves of peristalsis, which move from left to right over the baby’s belly as the stomach tries to empty itself against the thickened pylorus.

It’s important to contact your doctor if your baby experiences any of these symptoms.

Other conditions can have similar symptoms. For instance, gastroesophageal reflux (GER) usually begins before 8 weeks of age, with excess spitting up, or reflux — which may resemble vomiting — taking place after feedings. However, the majority of infants with GERD do not experience projectile vomiting, and although they may have poor weight gain, they tend to have normal stools.

A baby with allergy to milk protein may also spit up or vomit, as well as have diarrhea. However, these babies do not have projectile vomiting or vomit up bile.

In infants, symptoms of gastroenteritis — inflammation in the digestive tract that can be caused by viral or bacterial infection — may also somewhat resemble pyloric stenosis. Vomiting and dehydration are seen with both conditions; however, infants with gastroenteritis usually also have diarrhea with loose, watery, or sometimes bloody stools. Diarrhea usually isn’t seen with pyloric stenosis.

Diagnosis and Treatment

Your doctor will ask detailed questions about the baby’s feeding and vomiting patterns, including the appearance of the vomit. The most important part of diagnosing pyloric stenosis is a reliable and consistent history and description of the vomiting.

The baby will be examined, and any weight loss or failure to maintain growth since birth will be noted. During the exam, the doctor will check for a lump in the abdomen — which is usually firm and movable and feels like an olive. Doctors sometimes feel this lump and if they do, it’s a strong indication that a baby has pyloric stenosis.

If the baby’s feeding history and physical examination suggest pyloric stenosis, an ultrasound of the baby’s abdomen will usually be performed. The enlarged, thickened pylorus can be seen on ultrasound images. The doctor may ask that you not feed your baby for several hours before an ultrasound to look for pyloric stenosis.

Sometimes instead of an ultrasound, a barium swallow is performed. Babies swallow a small amount of a chalky liquid (barium), and then special X-rays are taken to view the pyloric region of the stomach to see if there is any narrowing or blockage.

Infants suspected of having pyloric stenosis usually undergo blood tests because the continuous vomiting of stomach acid, as well as the resulting dehydration from fluid losses, can cause salt and other imbalances in the blood that need to be corrected.

When an infant is diagnosed with pyloric stenosis, either by ultrasound or barium swallow, the baby will be admitted to the hospital and prepared for surgery. Any dehydration or electrolyte problems in the blood will be corrected with intravenous (IV) fluids, usually within 24 hours.

A surgical procedure called pyloromyotomy, which involves cutting through the thickened muscles of the pylorus, is performed to relieve the blockage that results from pyloric stenosis. The pylorus is examined through a very small incision, and the muscles that are overgrown and thickened are spread and relaxed.

The surgery can also be performed through laparoscopy. This is a technique that uses a tiny scope placed in an incision in the belly button allowing the doctor to see the area of the pylorus. With the help of other small instruments placed in nearby incisions, the surgery is completed.

Most babies are able to return to normal feedings fairly quickly, usually 3 to 4 hours after the surgery. Because of swelling at the surgery site, the baby may still vomit small amounts for a day or so after surgery. As long as there are no complications, most babies who have undergone pyloromyotomy can return to a normal feeding schedule and be sent home within 24 to 48 hours of the surgery.

If you are breastfeeding, you may be concerned about being able to continue feeding while your baby is hospitalized. The hospital should be able to provide you with a breast pump and assist you in its use so that you can continue to express milk until your baby can once again feed regularly.

After a successful pyloromyotomy, your infant will not need to follow any special feeding schedules. Your doctor will probably want to examine your child at a follow-up appointment to make sure the surgical site is healing properly and that your baby is feeding well and maintaining or gaining weight.

Pyloric stenosis should not recur after a complete pyloromyotomy. If your baby continues to display symptoms weeks after the surgery, it may suggest another medical problem, such as inflammation of the stomach (gastritis) or GERD — or it could indicate that the initial pyloromyotomy was incomplete.

When to Call the Doctor

Pyloric stenosis is an urgent condition that requires immediate evaluation. Call your doctor if your baby has vomiting and any of the following symptoms:

  • persistent or projectile vomiting after feeding
  • poor weight gain or weight loss
  • decreased activity or lethargy
  • few or no stools over a period of 1 or 2 days
  • signs of dehydration such as decreased urination (more than 4 to 6 hours between wet diapers)
  • sunken “soft spot” on the head; sunken eyes

Reviewed by: J. Fernando del Rosario, MD
Date reviewed: March 2014