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Pyloric Stenosis

  • Cynthia M. Johnson, MA
Publication Type:


Pyloric Stenosis

(Infantile Hypertrophic Pyloric Stenosis)


Pyloric stenosis is a narrowing of the pylorus, which is a muscle between the stomach and the intestines. It makes it hard for food to pass and for a baby to get proper nutrients and fluids. Early treatment can improve outcomes.

Pyloric Stenosis.

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The pylorus should open and close to allow stomach contents to pass from the stomach to the small intestine. With pyloric stenosis, the muscles thicken and make it hard for this process to happen. The reason why this happens is not known. Genes and the environment may play a role.

The pylorus is a valve that opens and closes during digestion. This allows partly digested food and other stomach contents to pass from the stomach to the small intestine.

The narrowing is caused by an enlarged muscle surrounding the pylorus. The reason why this happens is not known. It is believed to be the result of several factors, which may include:

  • Genetics
  • Structural defects that occur during fetal development
  • Bacterial infection, such as Helicobacter pylori

Risk Factors

Pyloric stenosis is more common in male babies, especially if they are firstborn. Other things that may raise the risk are:

  • Bottle feeding
  • Being born very early
  • A family history of pyloric stenosis
  • Early antibiotic use
  • Having a mother who smoked or drank alcohol during pregnancy


Pyloric stenosis is rarely present at birth. Symptoms usually start when a baby is 3 to 12 weeks of age. The most common symptom is forceful, projectile vomiting. This is due to the buildup of fluids in the stomach because they cannot pass into the small intestine.

Other problems may be:

  • Constant hunger
  • Weight loss
  • Signs of dehydration, such as passing less urine (pee), dry mouth, and crying without tears
  • Unusual sleepiness
  • Not passing stool (poop) often
  • Bloody vomit


The doctor will ask about symptoms and past health. A physical exam will be done. The doctor will examine the abdomen.

Pictures will be taken of the stomach, small intestine, and other structures. This can be done with:


The goal of treatment will be to correct the blockage. This can be done with a surgery called pyloromyotomy. It will divide the muscle of the pylorus to open it and allow food to pass. IV fluids and electrolytes will also be given to treat dehydration and electrolyte imbalances.


There are no current guidelines to prevent pyloric stenosis.





  • ASGE Standards of Practice Committee, Jue TL, Storm AC, et al. ASGE guideline on the role of endoscopy in the management of benign and malignant gastroduodenal obstruction. Gastrointest Endosc. 2021 Feb;93(2):309-322.
  • El-Gohary Y, Abdelhafeez A, et al. Pyloric stenosis: an enigma more than a century after the first successful treatment. Pediatr Surg Int. 2018 Jan;34(1):21-27.
  • Hypertrophic pyloric stenosis. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/hypertrophic-pyloric-stenosis.
  • SickKids clinical practice guideline on hypertrophic pyloric stenosis care pathway can be found at SickKids 2019 Jun 10. Available at: http://wapps.sickkids.ca/clinical-practice-guidelines/clinical-practice-guidelines/export/CLINS193/Main%20Document.pdf.


  • Elizabeth Margaret Prusak, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.