Age of Presentation of Hypertrophic Pyloric Stenosis
Hypertrophic pyloric stenosis (HPS) typically presents between 3 to 6 weeks of age in term infants, with peak incidence at 3-4 weeks of life. 1, 2
Typical Age Range for Term Infants
- Term infants with HPS classically present between 4 and 6 weeks of age, though symptoms can begin as early as 3 weeks 3, 2
- The condition is uncommon before 3 weeks of age, as pyloric muscle hypertrophy progresses after birth and requires time to reach complete gastric outlet obstruction 4
- HPS affects infants before the first three months of life, with the vast majority of cases occurring within this window 1
Adjusted Age for Premature Infants
Premature infants present at an older chronological age, and clinicians should calculate postconceptional age rather than chronological age when evaluating these patients. 3
- Greater degree of prematurity is significantly associated with older chronological age at presentation (P < .0001) 3
- When evaluating premature infants with nonbilious emesis, consider HPS if the calculated postconceptional age is between 44 and 50 weeks 3
- Premature infants represent approximately 7.3% of HPS cases and have increased postoperative morbidity compared to term infants 3
Early Presentation (Under 21 Days)
Approximately 19% of HPS cases present in newborns younger than 21 days of age, representing an important subset that requires modified diagnostic criteria 5
- Symptoms usually start after 3 weeks of age, making presentation before this time less common but clinically significant 4
- Younger infants (≤21 days) have significantly smaller pyloric measurements on ultrasound compared to older infants (muscle thickness 3.7 ± 0.65 mm vs 4.6 ± 0.82 mm, P < .05) 5
- Standard diagnostic ultrasound criteria (muscle thickness >4 mm, channel length >15 mm) may miss HPS in infants under 3 weeks, and a cutoff of 3.5 mm muscle thickness should be considered in this age group 5
Rare Delayed Presentations
- Delayed presentation of HPS beyond early infancy is extremely rare, with isolated case reports of presentation as late as 4.5 years of age 2
- Gastric outlet obstruction in childhood beyond the typical infant period occurs in only 1:100,000 cases 2
Clinical Pitfall to Avoid
Earlier diagnosis through increased use of ultrasound has changed the clinical presentation pattern, with infants now presenting with shorter duration of illness, less weight loss, less dehydration, and fewer metabolic abnormalities than historically reported 4. This means clinicians should maintain a high index of suspicion even when classic signs of severe dehydration and metabolic alkalosis are absent, particularly in the 3-6 week age window for term infants or 44-50 weeks postconceptional age for premature infants.