Gastric outlet obstruction

Alternative names
Congenital hypertrophic pyloric stenosis; Hypertrophic pyloric stenosis; Pyloric stenosis

Pyloric stenosis is a narrowing of the outlet from the stomach to the small intestine (called the pylorus). The condition primarily occurs in infants.

Causes, incidence, and risk factors

This condition is caused by a thickening of the muscles of the pylorus. This prevents the stomach from emptying into the small intestine.

The cause of the thickening is unknown, although genetic factors may play a role. It occurs more commonly in boys than in girls and is rare in patients older than 6 months.

Approximately 2 to 3 of every 1,000 infants has pyloric stenosis.


Symptoms generally appear several weeks after birth:

  • Vomiting       o Usually mild at first, becoming progressively more forceful within one half hour of feeding       o Projectile vomiting  
  • Infant appears constantly hungry  
  • Diarrhea (loose green stools)  
  • Wave-like motion of the abdomen shortly after feeding and just before vomiting occurs  
  • Dehydration (becoming more profound with the severity of the vomiting)  
  • Failure to gain weight or weight loss

Additional symptoms that may be associated with this condition:

  • Abdominal fullness prematurely after meals  
  • Belching  
  • Apparent abdominal pain

Signs and tests
Physical examination may show signs of dehydration. The infant may have a distended abdomen. Palpation of the abdomen may reveal the abnormal pylorus, which feels like an olive-shaped mass.

  • A chemistry panel often reveals electrolyte imbalances.  
  • An ultrasound of abdomen may be the first imaging test performed.  
  • A barium X-ray reveals a distended stomach and narrowed pylorus.


Treatment for pyloric stenosis involves surgery to split the overdeveloped muscles of the pylorus is the treatment for this disorder. Rehydration with intravenous fluids usually takes place prior to surgery.

Small, frequent feedings are usually well tolerated several hours after the surgery.

Expectations (prognosis)

Surgical repair usually provides complete relief of symptoms.


  • Postoperative vomiting (This is very common and generally improves with time.)  
  • Failure to gain weight in the newborn period  
  • Risks associated with any surgery

Calling your health care provider
Call your health care provider if symptoms suggestive of pyloric stenosis develop in your infant.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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