Pyloric Stenosis

The region of the stomach that connects to the duodenum of the small intestines is termed the "pylorus". In pyloric stenosis, the muscle of this region become hypertrophic and causes a gastrointestinal obstruction. 

Who Gets This?

The frequency of is 2-3.5 in 1000 live births, and males and Caucasian children, especially first-borns, are more commonly affected. Pyloric stenosis is also more commonly if there is a positive family history of the condition. 

When Does This Occur?

Pyloric stenosis occurs during the first 2-3 months of life, most often in the 2-4 weeks after birth.

Why Does This Occur?

The etiology of pyloric stenosis remains unclear. However, it is likely that both genetic and environmental factors play a role. Additionally, usage of erythromycin antibiotics in infants in linked with an increased risk of this condition. An association has also been found between infants whose breastfeeding mothers are taking erythromycin or who took the antibiotic in the later months of their pregnancy.



What Happens?

An infant with pyloric stenosis will typically have projectile, nonbilious vomiting. Because of this prolonged vomiting, the infant can have trouble gaining weight and can suffer from both dehydration and malnutrition. This vomiting can also lead to electrolyte imbalances, typically hypokalemia and hypochloremic metabolic alkalosis. Despite this vomiting, infants are typically hungry. 


How is this Diagnosed?

Presentation, physical exam, and imaging are all clues that suggest this diagnosis. Upon abdominal exam, the infant will commonly have a mass in the right upper quadrant (just above the level of the umbilicus). The mass is commonly olive-sized, muscular, mobile, and nontender.  On ultrasound examination of the thickness and length of this mass, a hypertrophic pylorus muscle can often be seen.  The classic "string sign" will be evident when contrast material is used. This term describes the elongated narrow pyloric channel that fills with contrast material

Pyloric stenosis as seen on ultrasound in a 6 week old

How is This Corrected?

Before surgery can be performed, the infant's dehydration and electrolyte abnormalities must be corrected, often with an NG tube placement. After this, a pyloromyomectomy is performed, where the circular muscles of the pylorus are transected.


Factors contributing to prolonged hospitalization of patients with infantile hypertrophic pyloric stenosis.
Tang KS, Huang IF, Shih HH, Huang YH, Wu CH, Lu CC, Huang FC, Tiao MM, Liang CD.
Pediatr Neonatol. 2011 Aug;52(4):203-7. Epub 2011 Jul 12.

Infantile hypertrophic pyloric stenosis: epidemiology, genetics, and clinical update.
Ranells JD, Carver JD, Kirby RS.
Adv Pediatr. 2011;58(1):195-206.

Pyloric stenosis: from a retrospective analysis to a prospective clinical trial - the impact on surgical outcomes.
St Peter SD, Ostlie DJ.
Curr Opin Pediatr. 2008 Jun;20(3):311-4. Review.