Pyloric Stenosis

What happens in pyloric stenosis

The pylorus is a ring of muscle between the stomach and the first part of the small intestine. It normally relaxes to let digested milk through. In pyloric stenosis, this muscle thickens and lengthens in the first weeks after birth, narrowing the channel. As feeding volumes increase, more milk is trapped, and the stomach contracts forcefully to push it out, causing projectile vomiting.

The exact cause is unknown. It is not caused by anything parents did, and it is not present at birth in most cases.

Risk factors

• Male sex, especially firstborn boys
• A parent or sibling who had pyloric stenosis, particularly the mother
• Exposure to the antibiotics erythromycin or azithromycin in the first 2 weeks of life
• Being born preterm and formula feeding have been associated in some studies

Pyloric stenosis symptoms

• Projectile vomiting: forceful vomiting that can travel a meter (3 feet) or more, usually within 30 to 60 minutes of a feed. It often starts as ordinary spitting up and becomes more frequent and forceful over days.
• Vomit is milk or curdled milk, not green.
• Hunger after vomiting: the baby wants to feed again straight away.
• Poor weight gain or weight loss.
• Signs of dehydration: fewer wet diapers, dry mouth, few tears, a sunken soft spot, lethargy.
• Fewer, smaller stools or constipation, because little milk reaches the bowel.
• Visible peristalsis: wave-like ripples moving across the upper belly from left to right just before vomiting.
• Olive-shaped mass: a firm, small lump in the upper belly that a doctor may feel when the baby is calm.

Pyloric stenosis vs reflux

Most babies spit up. Telling normal reflux from pyloric stenosis matters.

For more on everyday spit-up, see infant spitting up and gastroesophageal reflux.

Diagnosis

The doctor asks about the vomiting pattern, weighs the baby, checks for dehydration and gently feels the belly, sometimes during a test feed, for the olive-shaped mass.

• Abdominal ultrasound: the standard test. It measures the thickness and length of the pyloric muscle. A muscle wall of about 3 to 4 mm or more and a channel length of roughly 15 mm or more confirms the diagnosis.
• Blood tests: check for dehydration and the typical salt imbalance: low chloride, low potassium and an alkaline blood (metabolic alkalosis) from losing stomach acid.
• Upper GI contrast study: used only if ultrasound is unclear, or to look for other causes such as malrotation.

Treatment

Correct fluids first

Pyloric stenosis is urgent but not an immediate surgical emergency. The baby is admitted, feeding is stopped, and intravenous fluids correct dehydration and the salt imbalance, usually over 12 to 48 hours. Operating before the blood chemistry is normal raises anesthetic risk.

Pyloromyotomy

The surgeon cuts through the thickened outer muscle of the pylorus lengthwise, leaving the inner lining intact, so the channel opens. It is done through tiny keyhole (laparoscopic) incisions or a small cut near the belly button, takes under an hour and is done under general anesthesia.

After surgery

• Feeding usually restarts within a few hours, building up gradually.
• Some vomiting in the first day or two is common and usually settles.
• Most babies go home within 1 to 2 days.
• Pain is managed with acetaminophen (paracetamol) as directed by the team.
• Keep the wounds clean and dry and watch for redness, discharge or fever.

The muscle returns to normal size over weeks. Repeat surgery is rarely needed, and there are no long-term effects on digestion or growth.

Complications if untreated

Without treatment, ongoing vomiting leads to severe dehydration, dangerous salt imbalances, weight loss and failure to thrive. Early diagnosis has made these serious complications rare.

Frequently asked questions

At what age does pyloric stenosis occur?

It most often appears between 2 and 8 weeks of age, with a peak around 3 to 6 weeks. It is uncommon after 3 months. Premature babies may develop it a little later in terms of age from birth.

What does pyloric stenosis vomit look like?

It is forceful, projectile vomiting of milk or curdled milk, often shooting a meter or more, shortly after a feed. It is not green. Green vomit suggests a different, emergency bowel blockage. Over days the vomiting becomes more frequent and the baby remains hungry.

Can pyloric stenosis go away on its own?

Not reliably. A few countries have used medicine (atropine) in selected cases, but this takes longer and is less successful than surgery. In the US, pyloromyotomy is the standard treatment because it is quick, safe and nearly always curative.

How serious is pyloric stenosis surgery?

Pyloromyotomy is a common, low-risk operation in children's hospitals. It usually takes less than an hour, babies feed within hours, and most go home in 1 to 2 days. Complications such as wound infection or a small tear in the lining are uncommon and treatable.

Is pyloric stenosis genetic?

It tends to run in families. Children of a parent who had it, especially the mother, and siblings of affected babies have a higher risk. No single gene causes it, and environmental factors such as early exposure to some antibiotics also play a role.