Pyloric stenosis

Paediatric Surgical Abdomen, Dehydration & Child Protection / Non-Accidental Injury

Paediatric abdominal emergencies and clinical presentations of suspected non-accidental injury represent high-stakes diagnostic domains in Australian medical practice. Rapid differentiation between medical gastrointestinal disorders and time-sensitive surgical emergencies—such as hypertrophic pyloric stenosis and ileocolic intussusception—relies on anatomical principles and rigorous electrolyte correction. Concurrently, protecting vulnerable infants through the forensic recognition of physical abuse and executing statutory mandatory reporting duties are non-negotiable legal and ethical responsibilities.

Infantile Hypertrophic Pyloric Stenosis (IHPS)

Infantile hypertrophic pyloric stenosis (IHPS) is caused by marked hypertrophy and hyperplasia of the circular smooth muscle layers of the pylorus, resulting in severe anatomical narrowing and elongation of the pyloric canal with near-total gastric outlet obstruction.

Epidemiology and Presentation

• Demographics: Incidence is approximately 1 to 3 per 1,000 live births. Demonstrates a striking 4:1 male-to-female predominance and occurs most commonly in first-born male infants. There is a positive family history in 15% of cases and an association with maternal macrolide exposure (erythromycin, azithromycin) during late pregnancy or early lactation.
• Age of Onset: Classically manifests between 2 and 8 weeks of life (peak at 3 to 5 weeks); it rarely presents after 12 weeks.
• Cardinal Symptoms:
  • Non-bilious projectile vomiting: Occurs immediately after feeds (within 10 to 30 minutes). Initially intermittent, it rapidly progresses to forceful projectile ejection of curdled milk after every feed. The vomitus is strictly non-bilious because the obstruction lies proximal to the ampulla of Vater.
  • The "Hungry Feeder": In contrast to an infant with systemic sepsis or gastroenteritis who is listless and anorexic, an infant with IHPS remains ravenously hungry and demands to feed immediately after vomiting.
  • Progressive dehydration, constipation, and loss of weight (or failure to regain birth weight).

Physical Examination Findings

• Visible Peristalsis: Prominent gastric peristaltic waves can be observed travelling across the upper abdomen from left to right prior to emesis.
• The "Pyloric Olive": Palpation of a firm, mobile, nontender, olive-shaped mass approximately $2\text{ to }3\text{ cm}$ in diameter in the right upper quadrant or epigastrium (lateral to the right rectus muscle). Palpation is facilitated by calming the infant with a sucrose dummy or unhurriedly examining the abdomen immediately following gastric aspiration via an NG tube.

Pathophysiology of the Hallmark Electrolyte Derangement

Persistent emesis of gastric secretions causes profound fluid and biochemical disturbances characterized by hypochloraemic, hypokalaemic metabolic alkalosis with paradoxical aciduria:

1. Gastric juice contains high concentrations of hydrochloric acid ($HCl$). Vomiting loses hydrogen ($H^+$), chloride ($Cl^-$), and water, directly generating a hypochloraemic metabolic alkalosis ($pH > 7.45$, serum $HCO_3^- > 30\text{ mmol/L}$, serum $Cl^- < 90\text{ mmol/L}$).
2. Hypovolaemia activates the renin-angiotensin-aldosterone system (RAAS) to conserve sodium and vascular volume. In the distal renal tubules, aldosterone drives sodium reabsorption at the expense of accelerated potassium and hydrogen excretion, leading to profound systemic hypokalaemia.
3. Paradoxical Aciduria: As systemic potassium depletion worsens, intracellular tubular potassium stores are exhausted. To continue conserving sodium, the distal renal tubules are forced to excrete hydrogen ions ($H^+$) into the urine instead of potassium. Consequently, the urine becomes acidic ($pH < 6.0$) despite worsening severe systemic metabolic alkalosis.

Diagnostic Ultrasound

• Ultrasonography is the diagnostic gold standard (sensitivity and specificity $> 98\%$).
• Diagnostic Criteria:
  • Pyloric muscle wall thickness $\ge 3.0\text{ mm}$ (or $\ge 3.5\text{ mm}$ in older infants).
  • Pyloric channel length $\ge 14\text{ to }15\text{ mm}$.
  • Persistent failure of the pyloric lumen to open during active real-time observation.

Emergency Stabilization & Surgical Management

• Critical Clinical Rule: Pyloric stenosis is a MEDICAL emergency, NOT a surgical emergency. General anaesthesia in an alkalotic, dehydrated infant carries an unacceptably high risk of severe hypoventilation, postoperative apnoea (alkalosis depresses central respiratory drive), cardiac arrhythmias, and laryngospasm. Surgery must NEVER be performed until fluid deficits and metabolic alkalosis are completely normalized.
• Resuscitation Protocol:
  • Withhold all oral feeds (nil by mouth) and place a wide-bore nasogastric tube ($8\text{ to }10\text{ Fr}$) on free drainage with regular 4-hourly aspiration to decompress the stomach and prevent pulmonary aspiration.
  • Resuscitate hypovolaemia with an initial intravenous bolus of $10\text{ to }20\text{ mL/kg}$ of $0.9\%$ sodium chloride.
  • Administer maintenance and deficit replacement fluids using $0.9\%$ sodium chloride in $5\%$ glucose with $20\text{ mmol/L}$ potassium chloride (potassium chloride must only be added after confirming adequate renal urine output).
  • Resuscitate until laboratory markers confirm complete resolution: Serum chloride $> 100\text{ mmol/L}$, serum bicarbonate $< 28\text{ mmol/L}$, serum potassium $> 3.5\text{ mmol/L}$, and normal urine output ($> 1\text{ to }2\text{ mL/kg/hr}$).
• Definitive Surgery: Ramstedt pyloromyotomy (longitudinal incision of the hypertrophied pyloric muscle down to, but preserving, the underlying intact submucosa and mucosa). Can be performed open or laparoscopically. Feeding is cautiously reintroduced within 4 to 6 hours postoperatively.

Primary references (checked 7 October 2026): RCH pyloric stenosis.