• Clinical science

Hypertrophic pyloric stenosis


Hypertrophic pyloric stenosis – the most common cause of gastric outlet obstruction in infants – is characterized by hypertrophy and hyperplasia of the pyloric sphincter in the first months of life. Clinical manifestations usually appear between three and five weeks of age. The primary symptom is regurgitation progressing to nonbilious, projectile vomiting, which occurs intermittently or after feeding. The infant is irritable and demonstrates a strong rooting and sucking reflex because of hunger. Constant vomiting leads to hypokalemic and hypochloremic metabolic alkalosis. The diagnosis is usually clinical and involves the detection of a palpable "olive-shaped" structure in the epigastrium (a sign of marked hypertrophy of the pylorus) and visible gastric peristalsis proximal to the site of obstruction. The condition may also be diagnosed on ultrasound in the absence of a palpable “olive-shaped” structure. Initial management involves adequate rehydration and correction of electrolyte imbalances. The definitive treatment is Ramstedt pyloromyotomy.


  • Sex: > (∼ 5:1)
  • Peak incidence: 3–6 weeks of age (rarely presents after 12 weeks of age)


Epidemiological data refers to the US, unless otherwise specified.



Clinical features

  • Frequent regurgitation progressing to projectile, nonbilious vomiting immediately after feeding
  • An enlarged, thickened, "olive-shaped”, non-tender pylorus (diameter of 1–2 cm) should be palpable in the epigastrium
  • A peristaltic wave, moving from left to right, may be evident in the epigastrium
  • "Hungry vomiter": demands re-feeding after vomiting; , demonstrates a strong rooting and sucking reflex, irritable
  • If left untreated: dehydration, weight loss, failure to thrive



  • Initial imaging: Abdominal ultrasound → shows an elongated and thickened pylorus
  • Alternative imaging: If ultrasound is inconclusive
  • Laboratory tests

Nowadays, hypertrophic pyloric stenosis is diagnosed early and infants do not generally present with significant electrolyte imbalances!


Differential diagnoses

Differential diagnosis of newborn vomiting
Condition Findings
Hypertrophic pyloric stenosis
  • Regurgitation
  • Projectile, nonbilious vomiting
  • No diarrhea
  • Alkalosis and hypokalemia
Midgut volvulus and intestinal malrotation
  • Bilious vomiting
  • Abdominal distension
  • Signs of bowel ischemia: hematochezia, hematemesis, hypotension, and tachycardia in severe cases
Benign gastroesophageal reflux
  • Regurgitation and/or vomiting of food shortly after feeding
  • Healthy children with normal development
Gastroesophageal reflux disease
Congenital adrenal hyperplasia with salt loss
  • Vomiting, apathy, weight loss
  • Acidosis and hyperkalemia
Cyclical vomiting syndrome
  • ≥ 2 episodes of severe vomiting lasting a few hours or days, followed by normal healthy episodes in between lasting weeks to months

Benign gastroesophageal reflux (GER)

  • Etiology: temporary insufficiency of the lower esophageal sphincter
  • Clinical features
    • Regurgitation and/or vomiting of food shortly after feeds
    • Overall healthy appearance, normal development, no weight loss
  • Diagnostics: clinical diagnosis
  • Treatment
    • Positioning therapy: maintain upright position after feeding, avoid sitting or supine position
    • Thickening of food
  • Prognosis: very good; resolves spontaneously in the majority of cases by approx. 18 months of age

Gastroesophageal reflux disease (GERD)

  • Definition: GER associated with persistent symptoms and complications
  • Etiology: persistent insufficiency of the lower esophageal sphincter
  • Clinical features
  • Diagnostics: mainly a clinical diagnosis; imaging can be indicated if symptoms after initiation of empirical treatment persist
  • Treatment
    1. Conservative measures: positioning therapy and thickening of food (see “Treatment” section of GER above)
    2. Pharmacological treatment: H2-receptor blockers (e.g., ranitidine) and PPIs

Cyclical vomiting syndrome

  • Etiology: unknown
  • Presentation: recurrent attacks of severe vomiting; (bilious or non-bilious) with a typical pattern and no evidence of anatomical anomalies
  • Diagnostic criteria (both must be met)
    • At least 2 episodes of severe vomiting lasting a few hours or days
    • Normal health between episodes, which may last weeks or a few months
  • Treatment
    • Avoid possible triggers (e.g., foods such as cow's milk, cheese, or chocolate; stress)
    • Prophylactic treatment
    • Supportive care (e.g., IV fluids)


The differential diagnoses listed here are not exhaustive.


  • Conservative measures: before surgery
    • Correct electrolyte imbalance (e.g., replace K+)
    • IV rehydration
    • Frequent administration of small meals (12–24 per day)
    • Elevate head
  • Treatment of choice: Ramstedt pyloromyotomy (definitive management once the patient is rehydrated and electrolyte disturbances have been corrected)




last updated 09/13/2019
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