Children's Hospital Colorado

Hypertrophic Pyloric Stenosis

What is hypertrophic pyloric stenosis?

Pyloric stenosis occurs when the outlet of the stomach closes down, preventing normal movement of stomach contents into the small bowel. This condition is a common cause of infants vomiting undigested formula or breast milk.

How does hypertrophic pyloric stenosis cause children to vomit?

As a child eats, food travels from his or her mouth down the esophagus and into the stomach. The stomach acts as a reservoir, which slowly releases food into the small intestine.

However, in a child with pyloric stenosis the muscle that controls the flow of food from the stomach into the first part of the small intestine becomes enlarged, narrowing the outlet of the stomach. This narrowing inhibits food from passing into the small intestine and causes the infant to vomit.

If left untreated, hypertrophic pyloric stenosis can cause:

  • Dehydration
  • Electrolyte imbalance 
  • Lethargy

What causes hypertrophic pyloric stenosis?

This condition is caused by multiple factors including an infant's genetics and environment.

Who gets hypertrophic pyloric stenosis?

Pyloric stenosis is:

  • Fairly common, affecting about 1 out of 500 live births
  • Four times more common in males than females 
  • Tends to run in families

Get to know our pediatric experts.

Christy Kaczmarek, MPH/MSPH

Christy Kaczmarek, MPH/MSPH

Physician Assistant

Thomas Inge, MD

Thomas Inge, MD

Surgery - Pediatric, Surgery

Karisa Reynolds, PA

Karisa Reynolds, PA

Physician Assistant