Surgery chapters
Infantile hypertrophic pyloric stenosis
Hypertrophy of the pyloric muscle in young infants causing projectile non-bilious vomiting and hypochloraemic hypokalaemic metabolic alkalosis, corrected with fluids before a Ramstedt pyloromyotomy.
- Pyloric stenosis presents at 2–8 weeks (often a first-born boy) with projectile, non-bilious vomiting, a hungry baby, visible gastric peristalsis and a palpable olive; ultrasound confirms it.
- Loss of gastric acid gives hypochloraemic, hypokalaemic metabolic alkalosis with paradoxical aciduria.
- It is not a surgical emergency: rehydrate and correct the chloride, potassium and bicarbonate first, then do a Ramstedt pyloromyotomy.
On this page
Overview
Infantile hypertrophic pyloric stenosis (IHPS) is thickening (hypertrophy and hyperplasia) of the circular muscle of the pylorus that develops after birth. The narrowed, lengthened pyloric canal blocks the gastric outlet.
It is the commonest surgical cause of vomiting in early infancy. The exam focus is the age, the vomit, the metabolic picture and the order of treatment: fluids first, surgery second.
Epidemiology and risk factors
| Feature | Detail |
|---|---|
| Age | Usually 2–8 weeks (classically 3–6 weeks); rarely after about 13 weeks |
| Sex | Boys about 4 times more than girls; first-born boys classically |
| Inheritance | Multifactorial; children of an affected mother have a higher risk than children of an affected father (the less often affected sex carries more genetic load) |
| Other links | Positive family history; blood groups B and O (Basis of Paediatrics); erythromycin (macrolides) in the first weeks of life |
| Associations | Occasionally with other anomalies (e.g. tracheo-oesophageal fistula) |
Pathophysiology and the metabolic picture
The baby vomits stomach contents only (the block is above the ampulla of Vater), so the vomit contains no bile and loses H+ and Cl− (hydrochloric acid).
Step by step:
- Loss of HCl → hypochloraemia and a rise in plasma bicarbonate → metabolic alkalosis.
- Dehydration → aldosterone rises → the kidney keeps sodium and loses K+ (and H+) → hypokalaemia.
- With low chloride, the kidney must reabsorb sodium with bicarbonate, and must swap sodium for H+ or K+. When potassium runs low, it loses H+ → acidic urine despite an alkalosis: paradoxical aciduria (a late sign).
- Severe cases may show low sodium and raised urea from dehydration.
The classic picture is hypochloraemic, hypokalaemic metabolic alkalosis. Serum potassium may look near normal at first, even though total body potassium is low.
Congenital adrenal hyperplasia (salt-losing) also causes vomiting at a similar age, but gives hyperkalaemia, hyponatraemia and acidosis. Opposite potassium, opposite pH.
Some babies have mild unconjugated jaundice (reduced glucuronyl transferase), which settles after surgery.
Clinical features
- Projectile, non-bilious vomiting after feeds, getting worse over days.
- The baby is hungry and feeds eagerly straight after vomiting (unlike a baby vomiting from infection).
- Weight loss, dehydration (sunken fontanelle, dry mouth, few wet nappies), constipation, lethargy in late cases.
- Vomit may be coffee-ground from gastritis or oesophagitis.
Examination: the test feed
With the baby relaxed and feeding (or just after a vomit, when the abdomen is soft):
- Visible gastric peristalsis travelling left to right over the epigastrium.
- A firm, mobile "olive" (the hypertrophied pylorus), about 2 cm, felt in the right upper quadrant / epigastrium, above and to the right of the umbilicus, under the liver edge. Palpate from the baby's left side.
"Hungry, projectile, not green, with an olive."
Investigations
| Test | Finding |
|---|---|
| Ultrasound (investigation of choice) | Thick, long pyloric muscle; little or no passage of gastric contents. Commonly quoted cut-offs: muscle wall thicker than about 3–4 mm and channel longer than about 14–15 mm (cut-offs vary slightly between sources) |
| Barium meal (rarely now) | Narrow elongated canal: string sign, double tract sign (parallel lines of contrast), shoulder sign (muscle bulging into the antrum), delayed emptying |
| Blood gas and electrolytes | Low chloride, low potassium, high bicarbonate, alkalosis |
| Urea, glucose | Raised urea with dehydration; check glucose |
The diagnosis can be made clinically if an olive is felt; ultrasound confirms it when the examination is uncertain.
Differential diagnosis of vomiting in infancy
| Bile-stained vomiting (surgical until proven otherwise) | Non-bilious vomiting |
|---|---|
| Malrotation with volvulus | Pyloric stenosis |
| Duodenal atresia (below the ampulla), jejunal/ileal atresia | Gastro-oesophageal reflux (common, effortless, baby thriving) |
| Hirschsprung disease, meconium ileus | Overfeeding or poor technique |
| Intussusception (may be non-bilious at first) | Infection (UTI, meningitis, gastroenteritis), raised intracranial pressure |
| Incarcerated inguinal hernia | Congenital adrenal hyperplasia, metabolic disorders |
Pyloric stenosis vomit is never bilious. A baby with green vomit needs urgent assessment for malrotation with volvulus.
Management
1. Resuscitation first (not a surgical emergency)
- Stop oral feeds; pass a nasogastric tube (8–10 Fr) to empty the stomach.
- IV fluids: 0.9% saline with 5% glucose plus potassium chloride (0.15% KCl once passing urine). Bailey & Love describes 150–180 mL/kg/day for most babies.
- Replace NG losses mL for mL with 0.9% saline plus KCl.
- Shocked babies get a bolus of 0.9% saline first.
- Check electrolytes and gas regularly. Operate only when chloride, potassium and bicarbonate are back in the normal range (follow the local protocol for exact targets).
- Correction may take up to 48 hours if chloride is very low (85 mmol/L or less).
Rate 150–180 mL/kg/day: 4 × 150 = 600 mL/day; 4 × 180 = 720 mL/day
Hourly: 600 ÷ 24 = 25 mL/h to 720 ÷ 24 = 30 mL/h
Plus NG losses replaced mL for mL
Operating on an alkalotic baby is dangerous: alkalosis causes postoperative apnoea (it depresses breathing) and hypokalaemia causes arrhythmias. Never rush to theatre.
Pyloric stenosis is a medical emergency (dehydration, alkalosis), not a surgical emergency. Surgery waits until the biochemistry is normal.
2. Surgery: Ramstedt pyloromyotomy
- Through a supraumbilical (periumbilical) or right upper quadrant incision, or laparoscopically.
- The serosa and hypertrophied muscle are split along the length of the pylorus and spread apart, until the intact submucosa/mucosa bulges up, from the duodenum to the gastric antrum.
- The mucosa is not opened.
3. After surgery
- IV fluids until feeds are re-established, usually within 24 hours.
- Small vomits in the first few feeds are common and settle within about 72 hours.
- Persistent vomiting suggests an incomplete myotomy or reflux.
Complications
- Mucosal perforation at the duodenal end (the duodenal fornix): harmless if seen and repaired at once; dangerous if missed.
- Bleeding, wound infection, wound dehiscence, incisional hernia.
- Incomplete myotomy (persisting vomiting).
Prognosis is excellent, with no long-term effect on the stomach.
Expect: age at presentation (2–8 weeks), male predominance, projectile non-bilious vomiting in a hungry baby, left-to-right peristalsis and the olive, the acid-base picture (hypochloraemic hypokalaemic metabolic alkalosis) and paradoxical aciduria, the investigation of choice (ultrasound) and its findings, why fluid correction comes before surgery, the fluid used, the layer left intact in Ramstedt pyloromyotomy, differentiation from bilious vomiting and from congenital adrenal hyperplasia.
Quick revision
- Thick circular pyloric muscle develops after birth.
- 2–8 weeks, boys 4:1, first-born; erythromycin is a risk.
- Projectile, non-bilious; hungry baby; visible peristalsis left to right; olive.
- Hypochloraemic hypokalaemic metabolic alkalosis; paradoxical aciduria late.
- Ultrasound confirms; barium shows string and shoulder signs.
- NG tube, 0.9% saline + 5% glucose + KCl, correct before theatre.
- Ramstedt: split muscle, mucosa intact; feeds within a day.
Written by The House Job from standard references (Bailey & Love; Basis of Paediatrics).
FAQ
Why is the vomit in pyloric stenosis not green?
The block is at the pylorus, above the ampulla of Vater where bile enters, so only gastric contents are vomited.
What is paradoxical aciduria?
Acidic urine despite a metabolic alkalosis, because the kidney, short of chloride and potassium, keeps sodium by excreting hydrogen ions.
Is pyloric stenosis a surgical emergency?
No. The baby is first rehydrated and the electrolytes and alkalosis corrected, which can take a day or two, and then the pyloromyotomy is done.
Which layer is preserved in pyloromyotomy?
The mucosa (with submucosa) is kept intact; only the serosa and thick muscle are divided.