Suspected hypertrophic pyloric stenosis

ACR AC Vomiting in Infants

Ultrasound of the pylorus is the diagnostic test in an infant with non-bilious projectile vomiting. The vetting points are that this is an ultrasound question rather than a fluoroscopic or CT one, and that bilious vomiting is a different and more urgent problem.

An infant, typically between two and eight weeks old, with progressive non-bilious projectile vomiting, who remains hungry, with weight loss or poor weight gain.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

Paediatric abdominal ultrasound

What we'd amend, and why

Ultrasound images the pyloric muscle directly and in real time: the thickened hypoechoic muscle, the elongated channel and, decisively, the absence of gastric emptying watched over several minutes. It requires no radiation, no contrast and no sedation in an infant who is already dehydrated, and it simultaneously shows the alternative explanations for vomiting.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayinfant — Infants

Decision support only. Local protocol takes precedence.

Worth asking the referrer (1)

None of these hold the request up. They sharpen the protocol or the plan that follows.

Is the vomiting bilious?
Bilious vomiting redirects the pathway to urgent exclusion of malrotation and volvulus, which is a different study and a different level of urgency.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Infants

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	Paediatric abdominal ultrasound Paediatric abdominal ultrasound usually appropriate	Ultrasound images the pyloric muscle directly and in real time: the thickened hypoechoic muscle, the elongated channel and, decisively, the absence of gastric emptying watched over several minutes. It requires no radiation, no contrast and no sedation in an infant who is already dehydrated, and it simultaneously shows the alternative explanations for vomiting.
Second line	Upper GI contrast study Upper GI contrast study	A fluoroscopic upper gastrointestinal contrast study is the next step when the pylorus is normal but vomiting persists, and it is the urgent first study when the vomiting is bilious: it demonstrates the position of the duodenojejunal flexure — which should lie to the left of the vertebral pedicle at the level of the duodenal bulb — and so identifies malrotation, which ultrasound cannot exclude reliably. It has to be that study and not a contrast swallow: a swallow images the pharynx and oesophagus and never reaches the flexure, so a normal swallow in a bilious-vomiting infant is a normal report on a question nobody asked. Bilious vomiting in a neonate is a surgical emergency — malrotation with volvulus can infarct the whole midgut within hours — so this is booked immediately with the surgical team informed, never onto a routine fluoroscopy list. It carries a fluoroscopic dose and should be paediatric-protocolled with the shortest screening time that answers the question.
Problem solving	Contrast swallow / videofluoroscopy Contrast swallow	A different question, and the reason it sits at the bottom of this ladder rather than beside the upper gastrointestinal study: where the pylorus is normal, the duodenojejunal flexure is normal, and the history is of coughing, choking or colour change with feeds, recurrent chest infection or an unsafe swallow, the problem is aspiration rather than obstruction. A videofluoroscopic swallow assessed jointly with a speech and language therapist shows the swallow itself and whether the infant is aspirating, which no abdominal study can. It is not part of the pyloric work-up and should not be added to it — it is requested when the question has changed.

A borderline study in a convincing clinical picture should be repeated after a few hours rather than reported as normal; the muscle measurements evolve.
This ladder describes NON-bilious vomiting. Where the request states that the vomit is bilious, the order inverts: the upper gastrointestinal contrast study is the first and urgent examination, the pyloric ultrasound is not the answer, and redirecting that request to an ultrasound is the one correction on this card that can cost a child their bowel.

Pitfalls

Reporting borderline measurements as normal in a hungry vomiting infant instead of repeating the study.
Measuring an obliquely sectioned pylorus, which overestimates muscle thickness, or measuring a stomach so distended that the pylorus is displaced posteriorly and never properly seen.
Treating bilious vomiting as a pyloric question. That is malrotation until proven otherwise, it is time-critical, and the correct study is an urgent upper gastrointestinal contrast examination with the surgical team told — not a pyloric ultrasound, and not the next available fluoroscopy slot.
Booking a contrast SWALLOW when the question is malrotation. A swallow covers the pharynx and oesophagus and stops short of the duodenojejunal flexure, so it cannot answer the question and a normal result is meaningless — the study needed is an upper gastrointestinal series taken through to the flexure.
Requesting CT for a vomiting infant; it answers nothing here and the dose is unjustifiable.
Sending the infant straight to theatre on the imaging alone before the alkalosis and dehydration have been corrected.

Priors — what to pull first

Feeding history and the weight trajectory are more useful than any previous imaging in this age group.
A previous normal pyloric ultrasound early in the illness does not exclude the diagnosis later — the muscle changes progress.

What makes a good request

Pyloric stenosis is a medical emergency of dehydration and hypochloraemic alkalosis before it is a surgical one; the biochemistry must be corrected before theatre, so a same-day scan supports resuscitation rather than an immediate operation.
Bilious vomiting changes the question completely: malrotation with midgut volvulus is the diagnosis to exclude urgently, and that is an upper gastrointestinal contrast study, not a pyloric ultrasound.
Typical published diagnostic thresholds are a pyloric muscle thickness of about 3 mm or more and a channel length of about 15–17 mm, with the muscle thickness the more discriminating measurement. Thresholds vary between sources and with the infant’s age — confirm against local practice.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

Paediatric abdominal ultrasound Upper GI contrast study Contrast swallow

Confirm locally

Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.