Pyloric Stenosis

Aka: Pyloric Stenosis, Hypertrophic Pyloric Stenosis, Pyloric Stenosis Ultrasound, Infantile Hypertrophic Pyloric Stenosis, Congenital Stricture of the Pylorus

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II. Epidemiology

  1. Ages 3-6 weeks old (mean 3 weeks, up to 12 weeks of age)

III. Pathophysiology

  1. Hypertrophy of pylorus of the Stomach causing a gastric outlet obstruction

IV. Risk factors

  1. Family History of Pyloric Stenosis (especially northern european)
  2. Male gender (4 times more common than in girls)
  3. Other possible risk factors
    1. Bottle Feeding (Formula Feeding)
    2. Prematurity
    3. Maternal Tobacco Abuse
    4. Maternal Hyperthyroidism
    5. Macrolide Antibiotic use in the first 2 weeks of life

V. Symptoms: Vomiting

  1. Non-Bilious Vomiting that is more forceful than Spitting Up
  2. Starts intermittently
  3. Progressively increases in frequency and severity
  4. Infant remains hungry despite Vomiting
  5. Projectile Vomiting in up to 70% of cases

VI. Signs

  1. Typically, otherwise well appearing infant with benign Abdomen
  2. Palpable swelling ("olive") present in >60% of cases in past when delayed presentation was common
    1. In 2016 olive is rare due to early presentations
    2. Inferior to xiphoid process and inferior or deep to left liver edge

VII. Labs

  1. Basic metabolic panel
    1. Hypochloremic hypokalemic Metabolic Alkalosis
      1. Rarely seen due to early presentations in U.S.
    2. Other findings
      1. Hyponatremia
      2. Hypoglycemia
      3. Increased Renal Function tests (Serum Creatinine, Blood Urea Nitrogen)

VIII. Imaging: Pyloric Ultrasound

  1. Technique
    1. Linear probe in subxiphoid location, horizontal probe
    2. Look for gastric rugae, smooth outer serosal surface, slightly thicker wall
    3. Trace the outer surface of the Stomach down to the pylorus and duodenum
      1. Duodenal wall is much thinner than pylorus
  2. Diagnosis
    1. Thickened and elongated pylorus
      1. Pylorus wall thickness >3 mm
      2. Pylorus diameter >13 mm
      3. Pylorus length >15 mm (variable)
    2. No relaxation
    3. No fluid passage within channel
      1. May see very minimal flow (string sign)
  3. Efficacy
    1. Test Sensitivity and Test Specificity approach 100%

IX. Imaging: Miscellaneous

  1. Ultrasound (see above) is far preferred instead unless unavailable
  2. Abdominal XRay Findings
    1. Low Test Sensitivity
      1. Often normal despite Pyloric Stenosis
    2. Caterpillar sign (supine view)
      1. Serial large beeds of gas within a signifcantly distended Stomach
      2. Stomach persistalsis against a closed pylorus
    3. Left lateral decubitus findings
      1. Dilated Stomach distended by air (and/or fluid)
      2. Paucity of Small Bowel gas
    4. References
      1. Tubbs and Janicki (2025) Mastering Emergency Imaging, CCME, accessed 7/7/2026

X. Differential Diagnosis

  1. See Vomiting Causes in Children
  2. Pediatric Reflux
  3. Milk Protein Intolerance
  4. Intestinal Malrotation
  5. Small Bowel Obstruction

XI. Complications

  1. Pediatric Dehydration
  2. Hypochloremic hypokalemic Metabolic Alkalosis
    1. Rarely seen due to early presentations in U.S.

XII. Management

  1. Correct fluid and Electrolyte abnormalities
    1. Risk of postoperative apnea if not corrected
  2. Surgery (pyloromyotomy)
    1. Loosens pyloric Muscle

XIII. Resources

  1. Pyloric Stenosis Ultrasound
    1. https://vimeo.com/156797541

XIV. References

  1. Bukata (2013) Pediatric Emergencies, EM Bootcamp, CEME
  2. Nazer (2013) Pediatric Hypertrophic Pyloric Stenosis, EMedicine
    1. http://emedicine.medscape.com/article/929829-overview#showall
  3. Nirappil (2021) Crit Dec Emerg Med 35(8):12-3

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