Pyloric Stenosis

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OnSurg thanks collaborative partner Dr Anubhav Mittal at for making this valuable content available. Dr Mittal tweets at @anubhavnz.


In infantile hypertrophic pyloric stenosis (HPS), hypertrophy of the pyloric sphincter results in obstruction of the pyloric opening. It is the most common cause of gastric outlet obstruction in the 2- to 12-week-old age group. Pyloric stenosis leads to progressive emesis and projectile vomiting.


With prolonged vomiting, electrolyte and water loss leads to hypochloraemic, hypokalaemic alkalosis. Hypovolaemia leads to an increase in aldosterone and subsequent renal tubular absorption of sodium and water. This phenomenon results in a paradoxical loss of hydrogen and potassium ions. This alkalosis is worsened by renal absorption of bicarbonate. The severity of hypovolaemia and electrolyte abnormalities is directly proportional to the length of the symptoms prior to presentation. Indirect hyperbilirubinaemia is seen in 2% to 5% of infants due to a deficit in glucuronyl transferase activity.

Causes / Risk Factors

The aetiology remains elusive despite the disease prevalence. Genetic predisposition is not supported. Hyperacidity as a result of antral distention with feeding and hypertrophy of the pylorus from repeated contraction is believed to be a cause. Additionally, poor pyloric muscle neuronal innervation is believed to play a role. The lack of intestinal-pacemaker cells of Cajal is postulated to be another mechanism leading to pyloric stenosis. Nitric oxide synthase deficiency is also implicated as a biochemical cause, by decreasing smooth muscle relaxation. Previous reports also suggest that exposure to oral erythromycin is associated with significant odds of developing pyloric stenosis. However, none of these theories have yet been proven.


The success of surgical treatment is near 100% and complication rates are negligible. Therefore the prognosis from this condition is excellent.

Indirect hyperbilirubinaemia resolves with rehydration. Due to improved recognition, severe metabolic abnormalities are now less common.


GORD, Over-feeding, Malrotation, Acute infectious diarrhoea, Food allergy, Antral web, Duodenal atresia, Jejunoileal atresia, Pyloric atresia.

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