Pyloric stenosis

Definitions & Key takeaways

Pyloric stenosis is the narrowing of the opening from the stomach to the duodenum, often caused due to hypertrophy of the muscle surrounding this opening, which spasms when the stomach empties. Pyloric stenosis causes severe projectile nonbilious vomiting after meals, abdominal pain, poor weight gain, and dehydration. It usually presents in the first few months of life, and the thickened pylorus can be felt classically as an olive-shaped mass in the middle upper part or right upper quadrant of the infant's abdomen. Pyloric stenosis can be treated with pyloromyotomy, a surgical procedure that enlarges the pylorus.

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Introduction0:00–0:27

With hypertrophic pyloric stenosis, hypertrophy refers to an increase in size, pyloric refers to the pylorus which is the tissue between the stomach and the duodenum, and stenosis means narrowing, so hypertrophic pyloric stenosis, or HPS, is a congenital condition where a baby’s pylorus grows in size such that it narrows the tiny opening between the stomach and the duodenum.

Anatomy0:27–0:50

The pylorus itself has two parts to it, the pyloric antrum, which connects to the body of the stomach, and the pyloric canal, which connects to the duodenum.
At the end of the pyloric canal you’ve got the pyloric sphincter, which is a ring of smooth muscle that contracts and acts like a valve, letting food pass down into the duodenum, but not go back up into the stomach.

Pathology0:50–1:52

In HPS, babies are born with a normal pylorus, but within a few weeks after birth, the smooth muscle of the pyloric antrum begins to undergo hypertrophy and hyperplasia, meaning an increase in the size of each cell as well as an increase in the overall number of cells, respectively.
This causes the pyloric antrum to nearly double in size. This thick and muscular antrum obstructs the pathway of food, which makes it harder for food to leave the stomach and enter the small intestine.
Clinically the enlarged pylorus can be felt as an “olive” in the right upper quadrant or epigastric region of the abdomen, which is just above the umbilicus.
Also, there’s normally contraction and relaxation of the smooth muscle lining the stomach, a process called peristalsis.
Obstruction from HPS can cause the stomach smooth muscle to have to work much harder to push food through, and sometimes there can even be hypertrophy of those muscles, which can result in peristalsis that can be felt or seen.

Symptoms and complications1:52–3:09

If food can’t pass through the pylorus, it quickly starts to build up to the point where it has nowhere to go, which can lead to vomiting.
This usually happens around 2-6 weeks, and can get more intense over time, until it ultimately starts causing projectile vomiting, called that because the vomit literally launches out of a child’s mouth.
The vomit is also non-bilious, meaning it doesn’t contain bile, which makes sense, since bile secretion happens after the pyloric sphincter in the duodenum.
This vomiting leads to loss of stomach acid, which leads to dehydration, as well as loss of hydrochloric acid, which depletes the body’s chloride and leads to hypochloremia—low chloride in the blood.
Also, due to having a lowered blood volume from dehydration, the kidneys retain salt and excrete potassium, which results in hypokalemia—low potassium in the blood.
Hypokalemia results in a movement of potassium out of cells and hydrogen ions into cells, as well as secretion of hydrogen ions and reabsorption of bicarbonate ions in the kidneys.
These effects all tend to decrease the acidity of the blood, in other words increase the blood’s pH, resulting in metabolic alkalosis.

Causes3:09–3:27

The precise cause of HPS isn’t known, but likely involves genetic and environmental factors. For example it’s more likely among infant boys, and more common among first born children.
It has also been associated with exposure to macrolide antibiotics. Now, the diagnosis of HPS is usually based on identifying serious vomiting in an infant that’s a few weeks old, and feeling a small mass, or an “olive”, or begin able to see stomach peristalsis on a physical exam.

Diagnosis3:27–3:54

At that point, an ultrasound or other imaging studies like an X-ray can be used to confirm the disease. In addition, lab studies will classically show hypochloremic, hypokalemic metabolic alkalosis.

Treatment3:54–4:12

Treatment typically Initially involves good hydration and ensuring good electrolyte balance, but the definitive treatment is a pyloromyotomy, also known as Ramstedt’s procedure, where the muscle of the pylorus are cut and separated, allowing food to pass through more easily.

Review4:12–4:42

Alright, as a quick recap, hypertrophic pyloric stenosis is a congenital condition where a newborn’s pylorus undergoes hyperplasia and hypertrophy, leading to obstruction of the pyloric valve which causes vomiting (that might be projectile), as well as dehydration and metabolic alkalosis.
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