Projectile vomiting in a young baby is alarming the first time it happens. Milk travelling a metre across the room during a feed is not the normal posseting that parents are warned about. Pyloric stenosis is one cause, and it produces a characteristic and worsening pattern over days to weeks that parents and doctors learn to recognise.
The condition is important to diagnose promptly because it is progressive. A baby who is vomiting everything after every feed will become dehydrated and malnourished if not treated. But treated surgically, which is the standard approach, the outcomes are excellent.
Healthbooq (healthbooq.com) covers newborn and infant health conditions through the early months, including urgent conditions that parents need to recognise.
What Pyloric Stenosis Is
The pylorus is the muscular valve at the outlet of the stomach, through which partially digested food passes into the small intestine. In pyloric stenosis, the muscle surrounding the pylorus progressively thickens and tightens over the first weeks of life, narrowing the passage until milk can no longer get through.
The condition affects around 1 in 500 babies in the UK. It is four to five times more common in boys than girls. Firstborn children and children of mothers who had pyloric stenosis are at higher risk. There is a genetic component, though the exact mechanism is not well understood.
Pyloric stenosis is not present at birth: the pyloric muscle is of normal size in the first week or two of life. It develops over the following weeks, which is why symptoms typically begin at two to eight weeks rather than from birth.
The Characteristic Presentation
The vomiting in pyloric stenosis is projectile. Not a little dribble, not normal posseting, but forceful ejection of a full stomach's worth of milk. The baby then looks hungry and wants to feed again immediately. This cycle, full feed followed by complete vomiting followed by immediate hunger, is very distinctive.
The vomiting does not contain bile (the greenish-yellow fluid that comes from further down the intestine). This is because the obstruction is before the point where bile enters the digestive tract. Bile-stained vomiting in a young baby suggests a different and more urgent problem and needs emergency assessment.
Initially the vomiting may be intermittent. Over days to weeks it becomes consistent after every feed. The baby begins to lose weight or fail to gain, becomes increasingly hungry, and develops signs of dehydration as the obstruction worsens.
In some cases, visible waves of movement across the abdomen after a feed can be seen (gastric peristalsis): the stomach working hard against the obstruction. An olive-shaped mass in the right upper abdomen can sometimes be felt by an experienced clinician, though this sign is less commonly used now that ultrasound is available.
Diagnosis
The investigation of choice is an abdominal ultrasound, which directly images the pylorus and measures the thickness and length of the pyloric muscle. A pyloric muscle over 4 mm thick and 16 mm long is the commonly used diagnostic threshold.
Blood tests typically show a metabolic alkalosis with hypochloraemia and hypokalaemia, reflecting the loss of hydrochloric acid from the stomach with repeated vomiting. These electrolyte abnormalities need to be corrected before surgery.
Treatment
Pyloric stenosis is treated surgically by pyloromyotomy, a procedure first described by Conrad Ramstedt in 1912. The surgeon makes an incision through the outer layers of the pyloric muscle down to the inner lining, allowing the passage to open without cutting into the gut lumen. It can be done as an open procedure or laparoscopically (keyhole).
The surgery is not an emergency in the sense that it needs to happen within the hour, but it does need to happen. Before surgery, the baby is rehydrated and electrolytes are corrected, which typically takes 24 to 48 hours. Surgery then proceeds.
Feeding is usually restarted a few hours after the procedure, initially with small volumes and building up. Most babies go home within 24 to 48 hours of surgery and feed normally within a few days. Outcomes are excellent.
When to Seek Help
A baby of two to eight weeks who is vomiting forcefully after feeds, who appears hungry immediately after vomiting, and who is not gaining weight should be seen by a GP or taken to A&E for assessment. Do not wait for a scheduled appointment if the vomiting is worsening, the baby is losing weight, or signs of dehydration are developing (fewer wet nappies, sunken fontanelle, very dry mouth, lethargy).
Key Takeaways
Pyloric stenosis is a narrowing of the pylorus, the muscular valve between the stomach and the small intestine, that progressively obstructs the passage of milk from the stomach. It typically presents at two to eight weeks of age with worsening projectile vomiting after feeds, hunger immediately after vomiting, and eventually dehydration and weight loss. It is more common in boys and in firstborn children. Diagnosis is by ultrasound. Treatment is surgical (pyloromyotomy), which is curative and has excellent outcomes when performed before severe dehydration develops.
