Pyloric stenosis: infantile hypertrophic and acquired
- Lesion
In some infants the muscle of the stomach outlet grows too thick and blocks it; in adults scarring or cancer can do the same.
What it is
Infantile hypertrophic pyloric stenosis is a thickening of the muscularis propria of the pylorus that obstructs gastric emptying in the first weeks of life. It runs in families, is far more common in boys, and has been linked to early exposure to macrolide antibiotics. In adults, the pylorus narrows for other reasons: scarring from chronic antral gastritis or ulcers near the pylorus, or infiltration by gastric or pancreatic cancer.
Structure
- Gross: a firm, elongated, olive-like pylorus with a narrow canal.
- Micro: hypertrophy and hyperplasia of the smooth muscle of the muscularis propria.
- Mucosal and submucosal oedema and inflammation may tighten the canal further.
Step by step
- The pyloric muscle coat thickens in the first weeks after birth.
- The canal lengthens and narrows; feeds cannot leave the stomach.
- Forceful non-bilious vomiting follows each feed.
- Loss of gastric acid and fluid causes alkalosis, low chloride and low potassium.
- Surgical splitting of the muscle (pyloromyotomy) relieves the obstruction.
Clinical notes
- The baby is hungry and wants to feed again soon after vomiting.
- In an adult with gastric outlet obstruction, biopsy is needed to exclude cancer.
Test yourself
Think of the answer, then tap the question to see it.
Which layer is thickened in infantile hypertrophic pyloric stenosis?
The smooth muscle of the pyloric muscularis propria.
What acid-base disturbance does persistent vomiting in pyloric stenosis cause?
Hypochloraemic, hypokalaemic metabolic alkalosis.
What are the usual causes of acquired pyloric stenosis in adults?
Scarring from antral gastritis or peptic ulcers near the pylorus, and infiltrating distal gastric or pancreatic cancer.
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Pyloric Stenosis (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.