Pyloric stenosis



Pyloric stenosis or infantile hypertrophic pyloric stenosis (IHPS) is a narrowing of the pylorus leading to intestinal obstruction in infants.

it is caused by hypertrophy and hyperplasia of the pylorus (a muscular valve sitting between the stomach and duodenum). It classically presents with projectile non-bilious vomiting in infants 2-8 weeks old.

Surgical management with a pyloromyotomy (Ramstedt’s or laparoscopic) normally results in full resolution and minimal morbidity.


The incidence of IHPS is estimated to be 1 in 500 live births.

Figures vary from study to study and there appears to be a gradual decrease in the incidence of IHPS. A review by Pederson et al of seven European regions found an overall incidence of 2 in 1000 live births.

Most cases present in infants between the ages of 2-8 weeks old. A series of 362 patients reported by Taylor et al found a mean age at admission of 5.4 weeks. There were three presentations prior to 2 weeks (earliest 3 days old) and four after 12 weeks (latest 29 weeks old). In the same series, 84.8% of infants were male, a ratio of 5.6:1.

Aetiology & pathophysiology 

The aetiology of IHPS appears to be multifactorial involving both environmental and genetic factors.

Pyloric stenosis results from hypertrophy and hyperplasia of the pylorus. This acts as a mechanical obstruction to the outflow of gastric contents into the duodenum.

A number of apparent risk factors have been identified. Environmental factors include maternal smoking and bottle feeding (as opposed to breastfeeding). A familial component has also been identified and risk is increased significantly if siblings are affected.

Interestingly the use of macrolide antibiotics in infants has been shown to be associated with the development of IHPS, especially in the first two weeks of life. Maternal use in the two weeks following birth has also been associated with the development of the disorder.


Non-bilious vomiting is the hallmark feature of pyloric stenosis.

It is classically described as projectile though it is not always. Patients normally present at 2-8 weeks of age with vomiting, normally 30-60 minutes after being fed. The vomiting has often worsened over days with increasing intensity.

Some blood may be seen secondary to gastritis or a Mallory-Weiss tear associated with the vomiting. If presenting late, significant dehydration may have occurred with weight loss, decreased urinary output and lethargy.

On examination, the enlarged, firm pylorus is often palpable. It can be felt in the epigastrium or right upper quadrant and is often described as an olive. This is highly predictive of pyloric stenosis but may be absent, the series by Taylor et al found it was identified in 48% of cases. Visible or palpable peristalsis of the stomach is described in around 25% of cases, representing the stomach trying to contract against the thickened pylorus.


Abdominal USS is the diagnostic modality of choice for IHPS.


Blood tests can be used to evaluate the effects of vomiting. Vomiting leads to the loss of fluids rich in hydrogen chloride and potassium. The result is dehydration, commonly associated with a hypochloraemic, hypokalaemic metabolic alkalosis. Electrolytes should be measured to identify deficiencies.

  • FBC
  • Renal function & serum electrolytes
  • Capillary blood gas


Abdominal USS is normally readily accessible and provides an accurate assessment of the pylorus whilst avoiding ionising radiation.


IHPS is managed surgically with a pyloromyotomy.

Prior to surgery, appropriate fluid resuscitation should be given and electrolyte abnormalities corrected.

Pyloromyotomy is used to treat IHPS. It involves surgically approaching the pylorus and cutting the thickened muscle (myotomy) to release the stenosis. Great care is needed not to cause a mucosal injury. There are two main types of pyloromyotomy:

  • Ramstedt's pyloromyotomy: is the original procedure to treat pyloric stenosis, it has been performed for over 100 years. It is an open procedure performed through an incision in the RUQ.
  • Laparoscopic pyloromyotomy: more recently there has been a move towards a minimally invasive approach. At centres with appropriate expertise, this approach may be offered.

The procedure is safe and post-operative recovery typically excellent. The major complications are mucosal perforation, haematoma and wound infection.

Last updated: April 2022
Author The Pulsenotes Team A dedicated team of UK doctors who want to make learning medicine beautifully simple.

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