Summary

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.

Epidemiology

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

Approx. 40% of cases occur in first‑born infants.

The incidence is higher in white populations.

References:^[1]^[2]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

Environmental factors
- Exposure to nicotine during pregnancy
- Bottle feeding
Genetic factors: patients with affected relatives have a higher risk of hypertrophic pyloric stenosis
Macrolide antibiotics
- Erythromycin and azithromycin are associated with a higher risk of hypertrophic pyloric stenosis, especially when administered within 2 weeks after birth
- Hypertrophic pyloric stenosis associated with macrolide antibiotics should be reported to the Food and Drug Administration

References:^[2]^[3]^[4]

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

References:^[1]^[4]

Diagnostics

Initial imaging: Abdominal ultrasound → shows an elongated and thickened pylorus
- Elongated pylorus (normal: 15–17 mm)
- Thickened pylorus muscle (normal: < 3 mm)
- Pylorus transverse diameter (normal: < 13 mm)
- Impaired gastric peristalsis
- Protruding angular notch of the antrum
Alternative imaging: If ultrasound is inconclusive
- Barium studies
  - Narrow pyloric orifice
  - String sign: elongated pylorus
  - Beak sign
- Endoscopy
Laboratory tests
- Hypochloremic, hypokalemic metabolic alkalosis is a classic result, but now uncommon as the infants are more commonly diagnosed and treated early (see pathophysiology of acid-base disorders for more information)
  - Hypokalemia usually occurs in infants that have been vomiting for many days or even weeks
- Hyponatremia or hypernatremia may be present

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

References:^[1]^[4]^[5]

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	Regurgitation and/or vomiting of food shortly after feeding Poor appetite, weight loss, failure to thrive Abdominal pain/discomfort Wheezing, stridor, chronic cough, hoarseness
Gastroenteritis	Diarrhea Vomiting Possibly fever
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
- Regurgitation, vomiting
- Poor appetite, refusal to feed, weight loss, failure to thrive
- Abdominal pain/discomfort
- Crying and irritability
- Wheezing, stridor, hoarseness, chronic cough
Diagnostics: mainly a clinical diagnosis; imaging can be indicated if symptoms after initiation of empirical treatment persist
- Upper gastrointestinal imaging series (with barium contrast)
- Esophagogastroduodenoscopy with biopsies
- Esophageal pH monitoring
- Esophageal manometry
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
3. Surgery: fundoplication as a last resort

Cyclical vomiting syndrome

Etiology: unknown
Presentation: recurrent attacks of severe vomiting; 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)

References:^[6]^[7]

The differential diagnoses listed here are not exhaustive.

Treatment

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)

References:^[1]^[4]

Prognosis

Very good prognosis
Mortality rate: < 1%

References:^[1]^[8]