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Pyloric stenosis in infants
An infant a few weeks old with forceful non-bilious "projectile" vomiting after every feed, constant hunger and a hypochloraemic hypokalaemic alkalosis has pyloric stenosis; fluids and electrolytes are corrected first, and only then is a pyloromyotomy done — it is not emergency surgery.
Why it matters in the exam
The classic case is a first-born male infant aged 3–6 weeks who vomits forcefully after every feed, stays hungry and loses weight; sometimes an "olive" is felt in the epigastrium and peristaltic waves are seen. Exposure to erythromycin in the first weeks raises the risk. The exam checks that the vomiting is non-bilious — bilious (green) vomiting in an infant is a completely different emergency: malrotation with volvulus, which needs an upper gastrointestinal contrast study at once.
The second part is laboratory findings and treatment: a metabolic alkalosis with chloride and potassium depletion, and sometimes "paradoxical aciduria" as the kidney retains sodium at the expense of hydrogen. Diagnosis is by ultrasound — a pyloric muscle at least 3 mm thick and at least 15 mm long. Treatment starts with correcting dehydration and electrolytes (chloride-containing fluids, with potassium once urine is passed), because operating on an alkalotic infant endangers breathing after anaesthesia; only then is a Ramstedt pyloromyotomy done, usually laparoscopically.
Key points
- First-born male, 3–6 weeks, projectile non-bilious vomiting, hunger.
- Alkalosis with chloride and potassium depletion.
- Ultrasound: thickness 3 mm or more, length 15 mm or more.
- Fluids and electrolytes first, then Ramstedt pyloromyotomy.
- Bilious vomiting — malrotation with volvulus until proven otherwise.
Summary table
| Topic | Finding | Exam note |
|---|---|---|
| Who | First-born male, aged 3–6 weeks; early erythromycin exposure | Typical age — weeks, not months |
| Clinical picture | Projectile non-bilious vomiting after every feed, hunger, weight loss, "olive" | Bilious vomiting — think of malrotation |
| Laboratory | Metabolic alkalosis with chloride and potassium depletion; paradoxical aciduria | Correct before surgery |
| Imaging | Ultrasound: muscle thickness 3 mm or more, length 15 mm or more | The test of choice |
| Treatment | Chloride-containing fluids, potassium once urine is passed, then Ramstedt pyloromyotomy | Not emergency surgery |
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Sources
- Holcomb and Ashcraft's Pediatric Surgery, 7th edition (2020) — Hypertrophic Pyloric Stenosis
- Sabiston Textbook of Surgery, 21st edition (2022) — Pediatric Surgery
- ACR Appropriateness Criteria: Vomiting in Infants, 2019 — Imaging for non-bilious and bilious vomiting
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.