Hypertrophic pyloric stenosis

Hypertrophic pyloric stenosis is the most common cause of gastric outlet obstruction in infants. The condition manifests with postprandial nonbilious projectile vomiting, and symptom onset is typically between 2 and 6 weeks of age. On examination, an olive-shaped mass may be palpable in the epigastrium. The diagnosis is confirmed with abdominal ultrasound. Rehydration and correction of electrolyte derangements are required before definitive treatment with pyloromyotomy.

• Incidence: 0.5–5:1000 live births (considered to be the most common cause of gastric outlet obstruction in infants) ^[1]
• Sex: ♂ > ♀ (∼ 5:1)
• More common in firstborn children
• The incidence is higher in White populations. ^[2]

Epidemiological data refers to the US, unless otherwise specified.

• Environmental factors
  • Exposure to nicotine during pregnancy ^[2]
  • Bottle feeding ^[3]
• Genetic factors: Patients with affected relatives have an increased risk of hypertrophic pyloric stenosis.
• Macrolide antibiotics: Erythromycin and azithromycin are associated with an increased risk of hypertrophic pyloric stenosis, especially when administered within 2 weeks after birth.

• Onset: typically between 2 and 6 weeks of age (rarely after 12 weeks of age) ^[4][5]
• Symptoms ^[4]
  • Frequent regurgitation that progresses to projectile and nonbilious vomiting after feeding
  • Continued hunger after vomiting
  • Late stage: dehydration, poor weight gain, failure to thrive
• Physical examination ^[4]
  • Enlarged, thickened, nontender pylorus on palpation (described as olive-like)
  • Visible peristaltic waves in the epigastrium

Hypertrophic pyloric stenosis is suspected based on history and physical examination; imaging (e.g., abdominal ultrasound) is required for confirmation. ^[5]

Ultrasound abdomen ^[4][6]

• Indication: first-line for suspected hypertrophic pyloric stenosis ^[4][6]
• Findings ^[6]
  • Thickened pylorus muscle (≥ 4 mm)
  • Elongated pyloric channel length (> 18 mm)

Upper GI series ^[6]

• Indications ^[6]
  • Concern for bowel obstruction (e.g., midgut volvulus)
  • May be indicated for patients with suspected pyloric stenosis with nondiagnostic ultrasound
• Findings ^[6]
  • String sign: elongated pylorus with narrow lumen
  • Beak sign: distal tapering of the pylorus lumen
  • Shoulder sign: indentation of the antrum caused by the pylorus

Laboratory studies ^[4][5]

Assess for electrolyte derangements and dehydration with a BMP. The following findings are common in late-stage disease and uncommon in early disease:

• Hypochloremic, hypokalemic metabolic alkalosis
  • Loss of gastric hydrochloric acid due to emesis results in increased bicarbonate and decreased chloride concentrations in the blood.
  • Hypokalemia usually occurs in infants who have been vomiting for many days or even weeks.
• Hyponatremia or hypernatremia

Hypertrophic pyloric stenosis is now usually diagnosed early, and infants generally do not present with significant electrolyte imbalances.

The differential diagnoses listed here are not exhaustive.

Initial management ^[4][5]

• Establish NPO status.
• Initiate IV fluid resuscitation and/or IV maintenance fluids.
• Replete electrolytes (e.g., potassium repletion) as indicated.
• Consult surgery for pyloromyotomy.
• Admit for surgical management.

Pyloromyotomy ^[4][5]

• Definition: : a surgical procedure in which a longitudinal incision is made through the muscular layers of the hypertrophic pylorus to widen its lumen
• Indications: hypertrophic pyloric stenosis
• Contraindications: inadequate fluid resuscitation and electrolyte repletion
• Techniques
  • Laparoscopic pyloromyotomy (preferred)
  • Open Ramstedt pyloromyotomy
• Complications
  • Gastrointestinal perforation
  • Incomplete pyloromyotomy

Infants with uncorrected metabolic alkalosis are at increased risk of postoperative apnea and prolonged intubation. ^[5]

• Very good prognosis
• Mortality rate: < 1% ^[8]