U1.10.006 Hypertrophic pyloric stenosis

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Learning Objectives

  • Recognize hypertrophic pyloric stenosis as the most common cause of gastric outlet obstruction in infants.
  • Identify classic clinical signs, including a palpable olive-shaped mass, visible peristaltic waves, and postprandial nonbilious projectile vomiting.
  • Correlate electrolyte imbalances (hypokalemic hypochloremic metabolic alkalosis) and ultrasound findings with the diagnosis and management (pyloromyotomy).

1. Overview & Clinical Presentation

  • Definition: Caused by hypertrophy and hyperplasia of the pyloric sphincter muscle, creating a narrowed, thickened, and lengthened pyloric channel.
  • Epidemiology: Most common cause of gastric outlet obstruction in infants; more frequent in firstborn males and associated with early-life exposure to macrolides (e.g., erythromycin).
  • Symptoms (Presenting at 2–6 Weeks Old):
    • Postprandial nonbilious projectile vomiting.
    • Palpable olive-shaped mass in the epigastric region.
    • Visible peristaltic waves traveling across the upper abdomen.

2. Laboratory & Diagnostic Findings

  • Metabolic Derangement: Results in hypokalemic hypochloremic metabolic alkalosis secondary to the persistent vomiting of hydrochloric acid (gastric acid) and subsequent renal volume contraction/compensation.
  • Imaging: Ultrasound is the diagnostic modality of choice, demonstrating a thickened and lengthened pylorus.

3. Treatment

  • Surgical Intervention: Definitive treatment is a pyloromyotomy (surgical incision of the hypertroghed pyloric muscles).

Clinical Notes & Pearls:

  • Vomiting Type: Because the obstruction is proximal to the ampulla of Vater, the vomitus is strictly nonbilious (unlike lower intestinal obstructions which feature bilious vomiting).
  • Pre-op Optimization: Correct electrolyte and acid-base imbalances (hypokalemia and metabolic alkalosis) prior to performing surgery.
Key Points & Memory Hooks:
Classic Triad: Olive mass + nonbilious projectile vomiting + visible peristalsis at 2–6 weeks of age.
Lab Hallmark: Hypokalemic, hypochloremic metabolic alkalosis.
Treatment: Pyloromyotomy.

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