Pyloric Stenosis

The pyloric sphincter is a ring of smooth muscle the forms the canal between the stomach and the duodenumHypertrophy (thickening) and therefore narrowing of the pylorus is called pyloric stenosis. This prevents food traveling from the stomach to the duodenum as normal.

After feeding, there is increasingly powerful peristalsis in the stomach as it tries to push food into the duodenum. Eventually it becomes so powerful that it ejects the food into the oesophagus, out of the mouth and across the room. This is called “projectile vomiting”.


Pyloric stenosis typically presents in the first few weeks of life, with a hungry baby that is thin, pale and generally failing to thrive. The classic description of vomiting you should remember for your exams is “projectile vomiting”.

If examined after feeding, often the peristalsis can be seen by observing the abdomen. A firm, round mass can be felt in the upper abdomen that “feels like a large olive”. This is caused by the hypertrophic muscle of the pylorus

Blood gas analysis will show a hypochloric (low chloride) metabolic alkalosis as the baby is vomiting the hydrochloric acid from the stomach. This is a common data interpretation question in exams, so worth remembering.



Diagnosis is made using an abdominal ultrasound to visualise the thickened pylorus.

Treatment involves a laparoscopic pyloromyotomy (known as “Ramstedt’s operation“). An incision is made in the smooth muscle of the pylorus to widen the canal allowing that food to pass from the stomach to the duodenum as normal. Prognosis is excellent following the operation.


Last updated August 2019