Hypertrophic Pyloric Stenosis

Hypertrophic pyloric stenosis is hypertrophy and hyperplasia of the pyloric sphincter muscle. The condition is the most common cause of gastrointestinal obstruction in infants. Affected newborns typically present after the third to fifth week of life with progressive non-bilious vomiting and a firm, olive-like mass in the epigastrium. Ultrasound confirms the diagnosis based on the thickness and length of the pyloric muscle and channel diameter. Initial treatment consists of fluid resuscitation with correction of electrolyte imbalances, followed by either open or laparoscopic pyloromyotomy.

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Hypertrophic pyloric stenosis is a functional obstruction of the gastric outlet caused by hypertrophy and hyperplasia of both the circular and longitudinal layers of the pylorus in infants.

Hypertrophic pyloric stenosis

Hypertrophic pyloric stenosis

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  • The most common cause of intestinal obstruction in infants
  • Occurs in 13 in 1,000 infants in the United States
  • More common in whites, males, firstborns, blood groups B or O, and those with a positive history of pyloric stenosis in mother or father


  • Associations include eosinophilic gastroenteritis, Apert syndrome, Zellweger syndrome, trisomy 18, use of erythromycin in first 2 weeks of pregnancy, and maternal macrolide use during pregnancy or breastfeeding.
  • Reduced levels of neuronal nitric oxide synthase have been shown to be involved in the pathogenesis.

Clinical Manifestations


  • Initially, regurgitation after feeding
  • Later, non-bilious, projectile vomiting immediately after feeding
  • Usually starts after 3 weeks of age (range: 1 week to 5 months)
  • Poor weight gain
  • Infant shows signs of hunger (irritability, increased sucking reflex).


  • Firm, mobile, olive-shaped, 2-cm mass above and to the right of the umbilicus in epigastrium
  • Gastric peristaltic wave across the abdomen after feeding
  • Signs of dehydration including sunken fontanelles, delayed capillary refill, dry mucous membranes, and/or decreased urine output may be present.


Laboratory studies

  • Hypochloremic metabolic alkalosis
  • Hypokalemia
  • Elevated blood urea nitrogen (BUN) and creatinine with severe dehydration
  • Unconjugated (and occasionally conjugated) hyperbilirubinemia is the most common clinical association.


  • Diagnosis based on:
    • Pyloric muscle thickness: > 3 mm (the most discriminating and accurate criterion) 
    • Pyloric muscle length: > 15 mm
    • Pyloric diameter: > 15 mm

Contrast studies

  • If diagnosis not confirmed by ultrasound, but still suspected
  • String sign: elongated pyloric channel
  • Shoulder sign: pyloric bulging into channel
  • Double-track sign: parallel streaks of contrast in narrowed channel


Preoperative care

  • Fluid replacement + decompression
  • Correct electrolyte abnormalities
  • Restoration of acid-base balance


  • Ramstedt pyloromyotomy: short transverse skin incision plus longitudinal incision of pyloric muscle up to submucosa
  • Laparoscopy: equally effective with shorter hospital stay
Hypertrophic pyloric stenosis surgery

This is the classic definitive surgical treatment of hypertrophic pyloric stenosis called a “Ramstedt pyloromyotomy”, in which a longitudinal incision of the anterior surface of the pylorus is made down through the muscle layer only to the level of the submucosa, leaving the submucosa and mucosa in a prolapsed state.

Image by Lecturio.

Postoperative care

  • Oral feeding can be initiated within 1224 hours.
  • Persistent vomiting suggests incomplete pyloromyotomy or an alternative diagnosis.

Conservative approach

  • If surgery not tolerated or unavailable
  • Oral and intravenous atropine and cardiac monitoring → gradual introduction of feeding

Differential Diagnosis

  • Gastroesophageal reflux disease (GERD): a chronic disorder in which gastric acid, food, or fluids back up from the stomach into the esophagus. Patients often present with heartburn, bad breath, chest pain, and regurgitation. Gastroesophageal reflux disease can lead to damage to the teeth, esophagitis, and Barrett’s esophagus. Treatment includes lifestyle changes and medical therapy with antacids, proton pump inhibitors (PPIs), and prokinetics. 
  • Cyclical vomiting syndrome (CVS): a condition of unknown pathogenesis characterized by recurrent episodes of nausea, vomiting, and lethargy. Symptoms can last hours or days. Cyclical vomiting syndrome most commonly occurs in children but can affect individuals of any age. 
  • Gastroenteritis: inflammation of the gastrointestinal tract most often caused by viruses, but also bacteria or parasites. Symptoms usually last less than 14 days and include increased stool frequency or diarrhea, fever, vomiting, or abdominal pain. 
  • Congenital adrenal hyperplasia (CAH): a group of rare autosomal recessive diseases characterized by defects in enzymes of the adrenal glands involved in cortisol, androgen, and aldosterone synthesis. Patients may present with a wide range of symptoms, including virilization in females, salt-wasting leading to hypotension and other electrolyte abnormalities, and premature completion of growth resulting in short stature.
  • Increased intracranial pressure: a medical emergency defined by an intracranial pressure exceeding 20 mm Hg that can lead to a decrease in cerebral perfusion as well as herniation of the brain. Common symptoms include headache, vomiting, altered mentation, papilledema, and bradycardia. Causes include increased production or partially obstructed outflow of cerebrospinal fluid, bleedings, tumors, and infections.
  • Volvulus: a condition in which a loop of intestine twists around itself and the surrounding mesentery, causing bowel obstruction. Volvulus is often caused by a birth defect and presents early in life, but can occur at any age. Common symptoms include vomiting, abdominal pain and bloating, constipation, and bloody stool that may be gradual or sudden in onset. Emergency surgery is necessary to prevent necrosis of the intestinal structures.

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