Pyloric Stenosis

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Condition: Hypertrophic Pyloric Stenosis (HPS)

Overview (“What is it?”)

  • Hypertrophic pyloric stenosis (HPS) is a narrowing of the pylorus muscle. The pylorus is a sphincter muscle along the end of the stomach that controls the passage of food into the small intestine.  (See Figure 1.)

Figure 1: Normal Anatomy vs. Pyloric Stenosis

Figure 1

  • When the sphincter becomes hypertrophied (thicker than normal), the opening of the pylorus becomes too narrow for food or liquids to pass through.  This leads to excessive nonbilious (not green), projectile (“shooting out”) vomiting.
  • Hypertrophic pyloric stenosis is a relatively common condition that occurs more commonly in first-born male infants. It is believed to occur in approximately 1 in 300 to 900 live births.  
  • There is no known cause of HPS.
  • It appears to occur more frequently in males and may happen more often in the same family. However, most infants have no family history of HPS.

Signs and Symptoms (“What symptoms will my child have?”)

  • HPS is usually diagnosed between two to eight weeks of life. The most common symptom that is observed is worsening vomiting.
  • Projectile, (or forceful shooting) vomiting is the hallmark of HPS. The vomited fluid consists of formula. The vomiting may be intermittent at first, but will start to occur more often and can become projectile in nature. 
  • Your infant may continue to be hungry even after vomiting.
  • If vomiting continues over days, the baby can be dehydrated. The baby may not urinate as often and may not have tears when crying.
  • Blood levels of electrolytes (minerals such as sodium, bicarbonate and potassium) in the blood can be abnormal because of losses during vomiting. 

Diagnosis  (“What tests are done to find out what my child has?”)

  • HPS may be diagnosed by physical exam where the pylorus can be felt by pressing on the abdomen.
  • Most times an ultrasound will be performed to diagnose HPS. Ultrasound uses sound waves to create images of the pylorus which is seen to be longer and thicker than normal and does not allow liquid in the stomach to go through.
  • Less commonly, a radiological test called an upper gastrointestinal contrast study may be performed. The baby takes a liquid that lights up on X-ray. X-ray pictures of the stomach is taken. In HPS, only a very small amount of contrast gets out of the stomach. (See Figure 2)
Figure 2: Upper gastrointestinal study from a 6-week-old infant shows narrowing of the pyloric channel and the string sign in the pylorus

Treatment (“What will be done to make my child better?”)

  • The treatment for HPS is a surgical procedure called a “pyloromyotomy". The goal of the surgery is to make a cut in the thickened pylorus muscle and open the passage between the stomach and the small intestine. The surgery may be done laparoscopically or open.
    • Laparoscopic pyloromyotomy:  Several small cuts (incisions) are made. Through one of the cuts, a video camera is placed. The surgery itself is done using small instruments placed through the other incisions. Sometimes the surgery cannot be performed laparoscopically.
    • Open pyloromyotomy (Figure 3):  A cut is made usually in the right upper part of the belly or around the belly button. The pyloromyotomy involves making a cut through the thickened pyloric muscle while leaving the inside layer intact. This will allow food to pass through the pylorus and into the small intestine.
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.
    • Risks of undergoing surgery include, but are not limited to: the risks of anesthesia, bleeding, infection and unintended damage to other structures in the body. The inside lining of the stomach may also be cut during the pyloromyotomy. This will be repaired and it may take a longer to start feeding the baby in order to allow the area to seal. An additional risk of the surgery is that an inadequate incision is made in the pylorus muscle. This is rare and a second surgery may be required to correct this.
    • Benefits:  The stomach will be able to empty food into the small intestine, and the baby will be able to eat without vomiting.
  • Preoperative preparation:  Before surgery can be performed, the infant must be given additional fluids to improve the dehydration and correct abnormalities of the electrolyte (mineral) levels in the blood stream. Correcting these problems will make the baby better tolerate surgery and anesthesia better.  
  • Postoperative care:  The baby will be allowed a few hours to recover from anesthesia and allowed to drink at the discretion of the surgeon. For pain, the baby is given acetaminophen (Tylenol®).

Home Care (“What do I need to do once my child goes home?”)

  • Vomiting may still occur initially after surgery, but will usually resolve. 
  • Feeding is typically started around 4-6 hours after the surgery. Your surgeon will discuss the feeding plan after surgery.
  • If all goes well, your infant will be discharged within one day of surgery.
  • Surgical incisions should be kept clean and dry for three days after surgery. Afterwards, the wounds may be washed with soap and water but not soaked for about seven days after surgery. Most of the time, the stitches used in children are absorbable and do not require removal.
  • Follow-up:  You will follow up with the pediatric surgeon afterwards to make sure your infant is eating well, gaining weight and healing incisions.
  • When to call your doctor:  Redness or drainage of the wound, fevers, vomiting often, swelling of the belly.

Long-Term Outcomes (“Are there future conditions to worry about?”)

Long-term outcomes are excellent with a very low rate of complications. 


  1. Chung, Dai. "Pediatric Surgery." Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice. 19th ed. Saunders, 2012. 1821-1871. Print.
  2. Hackham, David J., Tracy C. Grikscheit, Kasper S. Wang, Kurt D. Newman, and Henri R. Ford. “Pediatric Surgery.” Schwartz's Principles of Surgery. 9th ed. McGraw-Hill. 2012. 1409-1447. Print.
  3. Sato, Thomas T., Oldham, Keith T. “Pediatric Abdomen.” Greenfield’s Surgery: Scientific Principles & Practice. 5th ed. Lippincott Williams & Wilkins. 2010. Print.

Updated: 11/2016
Author: Romeo C. Ignacio, Jr., MD: A. Kastl, MD
Editors: Patricia Lange, MD; Marjorie J. Arca, MD