Hypertrophic Pyloric Stenosis or HPS, is a condition in which there is a thickening of the muscle in the wall of the intestine, just beyond the stomach.
A child with HPS will experience increasing numbers of large milky vomits, and will vomit within half an hour of every single feed. Immediately after vomiting, the baby will be hungry again. This is one of the reasons why children with HPS are also associated with Infant Reflux (gastro-oesophageal reflux).
HPS is not a painful condition, however, it is potentially a life threatening one, as the babies can become dehydrated very quickly. HPS occurs in approximately 1 in every 350 babies and occurs most commonly between the ages of 2 and 10 weeks. It occurs more commonly in boys than girls, and in children of parents who had HPS when they were babies.
A baby that is developing HPS may not thrive well and may in fact lose weight. A baby who is becoming dehydrated will have fewer and fewer wet nappies and as no food/milk is going through the gut, the baby will have less and less soiling of its nappies. With increasing dehydration, the baby will become irritable and then will eventually become quiet and listless, with sunken fontanelles, dry mouth and lips and reduced elasticity of the skin.
The cause of HPS is essentially unknown, however, there are a number of theories that have been suggested. Many of these theories suggest an absence, or a deficiency of particular proteins or chemical message receptors in the muscle of the gut which is affected. The part of the gut that is affected is approximately 2 cm long and is called the pylorus.
When a paediatric surgeon examines a baby with HPS, he may see waves of stomach contractions. When he feels the abdomen after the baby is given a feed, he should be able to feel the thickened muscle in the upper part of the abdomen.
An ultrasound of the pylorus is the most accurate and safest test that can be performed to confirm the diagnosis. The standard operation for HPS is called a Pyloromyotomy, which is performed via a small cut in the abdomen usually at the level of the belly button. The aim of the operation is to cut the muscle of the pylorus and to stretch it far enough apart, so that it no longer causes an obstruction to the drainage of milk from the stomach.
The prognosis following the operation for HPS is excellent and the baby is usually feeding normally within two days. Sometimes, after the operation the baby will continue to vomit intermittently. This is usually due to reflux of milk, or in other words gastro-oesophageal reflux, which will have been present even before the pyloric stenosis developed.