Pyloric Stenosis
Pediatric Surgery
Illness script · Pediatric Surgery
Pyloric Stenosis
Hypertrophy of the pyloric muscle causing progressive gastric outlet obstruction in infants, typically 2–8 weeks of age.
This illness script for Pyloric Stenosis covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common surgical cause of vomiting in infants
- Male > female (4:1); firstborn males most affected
- Higher incidence in White infants
- Positive family history (maternal > paternal)
- Associated with macrolide antibiotic use (erythromycin) in neonatal period
02
Presentation
- Nonbilious, projectile vomiting after feeds; onset 2–8 weeks of life
- Progressive worsening — infant hungry immediately after vomiting ('hungry vomiter')
- Visible peristaltic waves across epigastrium (left to right)
- Palpable 'olive-shaped' mass in epigastrium (pathognomonic if present)
- Dehydration, poor weight gain, hypochloremic hypokalemic metabolic alkalosis
03
Pathophysiology
- Idiopathic hypertrophy and hyperplasia of pyloric circular muscle
- Progressive narrowing of pyloric channel → gastric outlet obstruction
- Repeated vomiting causes loss of H⁺ and Cl⁻ → hypochloremic metabolic alkalosis
- Paradoxical aciduria: kidneys retain H⁺ to preserve Na⁺/volume in late stages
04
Diagnostics
- Ultrasound is first-line and gold standard: pyloric muscle thickness ≥4 mm, channel length ≥17 mm
- Labs show hypochloremic, hypokalemic metabolic alkalosis with paradoxical aciduria
- Upper GI series (if US equivocal): 'string sign' or 'shoulder sign'
- Correct electrolytes BEFORE surgery — do not rush to OR with alkalosis
05
Management
- Resuscitate first: IV fluids (NS + KCl) and correct metabolic alkalosis before OR
- Definitive treatment: Ramstedt pyloromyotomy (surgical or laparoscopic)
- Early feeds post-op — majority tolerate feeds within hours
- Do NOT attempt medical management alone; surgery is curative
- Prognosis excellent; recurrence after adequate pyloromyotomy is rare
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Gastroesophageal Reflux Disease (GERD)
GERD vomiting is non-projectile, not progressive, and labs/US are normal
Malrotation with midgut volvulus
Volvulus causes BILIOUS vomiting — nonbilious vomiting strongly favors pyloric stenosis
Pyloric atresia
Atresia presents at birth (day 1), not the classic 2–8 week onset of stenosis
Adrenal insufficiency (CAH, salt-wasting)
CAH causes hyperkalemia and hyponatremia; pyloric stenosis causes hypokalemic alkalosis
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.