Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis, is the most common cause of non-bilious vomiting in children.

It is the result of hypertrophy of the pylorus muscles of the stomach leading to gastric outlet obstruction. Typically, infants are well at birth and then from 2-8 weeks of age develop increasingly frequent and forceful vomiting. This can lead to dehydration and weight loss.

The exact aetiology of pyloric stenosis is unknown but there are a number of risk factors that increase the likelihood of an infant developing the condition.

The definitive management is surgery.


  • Incidence: 4.00 cases per 100,000 person-years
  • Most commonly see in infants
  • Sex ratio: more common in males 4:1
Condition Relative
Gastro-oesophageal reflux in children12.50
Pyloric stenosis1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+


The exact aetiology of pyloric stenosis is unknown. The condition occurs in around 2 to 5 in 1000 live births. Risk factors include:
  • Male sex
    • There is a 4:1 male predominance
  • Being a firstborn child
  • Family history of pyloric stenosis
    • One study showed the heritability of the condition to be 87%
  • Maternal smoking
  • Bottle feeding
  • Preterm birth
  • Ethnicity
    • It is more common in the Caucasian and Hispanic populations and is rare in African, Asian and Indian infants
  • Erythromycin
    • There is an association between the use of erythromycin in the first two weeks of life and an increased risk of pyloric stenosis
    • A link between maternal macrolide use and increased incidence of pyloric stenosis has not been consistently demonstrated.

Clinical features

The clinical features of pyloric stenosis are:
  • Increasingly forceful and ultimately projectile non-bilious vomiting
    • The vomiting usually occurs immediately following a feed and the child is often extremely hungry and irritable after the episode.
    • The course of the disease is variable. Some children can become sick very quickly and others develop increasingly forceful vomiting over a period of days - weeks. The typical symptoms usually develop during the third week of life.
  • Haematemesis in around 10% of cases
    • Due to reflux oesophagitis resulting from gastric outlet obstruction
  • Weight loss or inadequate weight gain
    • Occurs in infants with delayed presentation
  • Dehydration
    • Vomiting leads to severe hypochloraemic, hypokalaemic dehydration with metabolic alkalosis
    • Signs of dehydration in infants include sunken fontanelles, sunken eyes, dry mucous membranes, poor skin turgor, decreased tearing, lethargy, tachycardia, prolonged capillary refill time, and decreased urine output
    • Can predispose to pre-renal acute kidney injury
  • Stool changes
    • Often small and hard, sometimes the child passes little to no stool
  • Firm, non-tender 1-2cm mass in the right upper quadrant of the abdomen
    • As a result of the thickening of the pylorus muscles, often described as an 'olive'
  • Visible peristalsis
    • May become more prominent following a feed
  • Parents may have tried multiple formula changes
    • This is due to initial symptoms being vague and similar to formula intolerances.


Pyloric stenosis is usually a clinical diagnosis and therefore suspicion demands a thorough history and examination. The classical triad of a palpable pyloric mass, visible peristalsis, and projectile vomiting are not always present. Examination should include an assessment of the degree of dehydration. Weight and height should be plotted on a growth chart and compared with previous weights.

There are no specific guidelines for the investigation and management of pyloric stenosis. The following investigations are recommended:
  • Bloods
    • Urea and electrolytes to assess the degree of dehydration, electrolyte imbalance, and whether there is evidence of acute kidney injury
    • There is often a hypochloraemic metabolic alkalosis with severe potassium depletion
  • Ultrasonography of the abdomen
    • Sensitivity of ultrasound in diagnosing pyloric stenosis has been reported to be 97-99%
    • A positive test is pyloric thickness >3mm and pyloric length >15-17mm (based on measurements for term infants - pyloric canal length is shorter in premature infants)
    • A 'target sign' is often described on ultrasound - this is due to hypertrophied hypoechoic muscle surrounding echogenic mucosa

Differential diagnosis

The causes of vomiting in an infant are broad and diagnosis requires a high index of suspicion alongside thorough history and examination. Other causes of vomiting in this age group include:
  • Intestinal malrotation and volvulus
    • Presents with intermittent bilious vomiting associated with abdominal distension, haemodynamic instability, and severe abdominal pain due to bowel ischaemia.
  • Duodenal atresia
    • May present with either bilious or non-bilious vomiting depending on whether the atresia is distal to the ampulla of vater or not.
    • Classically shows the 'double-bubble sign' on x-ray.
  • Necrotising enterocolitis
    • More common in premature infants.
    • Acute life-threatening emergency presenting with poor feeding, abdominal distension, bilious vomiting, and haematochezia.
    • Can lead to intestinal perforation causing peritonitis, sepsis, and death.
    • 'Pneumatosis intestinalis' is the classical x-ray finding.
  • Tracheoesophageal fistula
    • Presentation depends on type.
    • Associated with other birth defects in the VACTERL association.
    • Presents with cough, recurrent pneumonia, cyanotic episodes when feeding, and respiratory distress.
  • Meconium ileus
    • Associated with cystic fibrosis.
    • Presents with intestinal obstruction and bilious vomiting within hours of birth.
  • Hirschprung disease
    • A birth defect characterised by complete absence of neuronal ganglion cells from a section of the intestine.
    • Presents with failure to pass meconium in the first 48 hours, severe or complete constipation, abdominal distension, and bilious vomiting.
  • Anorectal anomalies
    • Can cause bilious vomiting if not identified at the newborn and infant physical examination.
    • Also associated with the VACTERL association of birth defects.
  • Gastroesophageal reflux disease (GORD)
    • Reflux associated with worrying symptoms or complications such as uncontrollable crying, abdominal pain, arching of the back, food refusal, choking, respiratory symptoms, poor weight gain, and sleep disturbance.
  • Non-gastrointestinal causes:
    • Infection - gastroenteritis, meningitis, pyelonephritis, and sepsis may present with vomiting.
    • Milk protein allergy
    • Inborn errors of metabolism
    • Congenital adrenal hyperplasia
    • Intoxication/ poisoning


Pyloric stenosis is usually first noticed at home. Parents may notice forceful vomiting after feeds or signs of dehydration. Parents may bring their child to see the GP or attend the emergency department.

There is no consensus guidelines on the management of pyloric stenosis. The definitive management is pyloromyotomy. Initial management includes:
  • Fluid resuscitation
    • Surgery must be delayed until hypovolaemia and electrolyte disturbances are corrected.
    • If alkalosis is not corrected the risk of postoperative respiratory depression is increased. This is because patients with a metabolic alkalosis will respond with a respiratory acidosis resulting in postoperative apnoea.
    • If clinically shocked the patient should receive an initial fluid bolus prior to initiating maintenance fluids.
    • Maintenance fluids should be initiated at 150% of the normal maintenance rate for the infant's weight.
  • Surgery
    • Pyloromyotomy involves the extra mucosal longitudinal splitting of the pylorus muscle.
    • Surgery can be performed both laparoscopically and open with the laparoscopic method providing shorter recovery times and fewer analgesia requirements.

A nasogastric tube is also passed pre-operatively and put on free drainage. Any losses from the nasogastric tube must also be replaced ml by ml as IV fluids.

As there is no consensus guideline post-operative management will depend on local protocols. Infants will usually be started on reduced feeds and these will be slowly increased to full feeds. Vomiting is common postoperatively.


The complications of pyloric stenosis are directly related to the symptoms and how late the condition presents. Vomiting can lead to dehydration, weight loss, and electrolyte disturbance (hypochloraemic hypokalaemic metabolic alkalosis).

The complications of pyloromyotomy include:
  • Anaesthetic risk
  • Persistent vomiting due to incomplete pyloromyotomy
  • Mucosal perforation
  • Surgical site infection
  • Foveolar cell hyperplasia (a rare case of persistent gastric outlet obstruction)