First and second year — the floor first, then every step
Find the pylorus to the right of the gastric antrum, measure the single muscle wall and the channel length on a true longitudinal view, and watch it for several minutes — a channel that opens and lets fluid through is not stenosis.
Commonly used thresholds: single muscle wall thickness ≥ 3 mm and channel length ≥ 15 mm (verify the local cut-offs).
Pylorospasm mimics it transiently — dynamic observation separates them.
Acquire the study
Linear probe; infant supine or right-side-down; a small feed of clear fluid helps distend the antrum.
The manoeuvre
Locate the gastric antrum and follow it to the pylorus, medial to the gallbladder.
Longitudinal view: measure the single muscle wall thickness (hypoechoic layer) and the channel length.
Transverse view: the "target" or "doughnut" appearance and wall thickness.
Watch for several minutes: does fluid pass through the channel?
Gastric distension and hyperperistalsis.
What confirms it
Muscle thickness and channel length at or above the thresholds, with no passage of fluid over several minutes.
What licenses you to exclude it
A pylorus that opens with fluid passing and normal measurements excludes it; consider reflux or malrotation instead.
The classic misread
Measuring obliquely — the wall over-reads.
Calling pylorospasm stenosis without dynamic observation.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Diagnostic criteria
Pylorus · single-wall pyloric muscle thicknessunder 3 mm
Measure the single wall, not both; an oblique section over-reads. Judge with channel length and non-emptying.
USG · paediatric
Pylorus · pyloric channel lengthunder 15–17 mm
Measure during a real-time observation of non-emptying, not on a single frozen frame.
USG · paediatric
Pylorus (how to use the numbers) · How to apply the registered pyloric millimetres
the muscle-thickness and channel-length entries listed separately are the numbers; this entry exists so they are not applied without a gastric-outlet clinical picture and a non-overfilled stomach
An over-measured pylorus on a crying, overfilled stomach is a false positive. Do not invent new millimetres; use the registered pair with this caveat.
USG · paediatric
Pylorus (companion caveat) · How not to invent a second pyloric number
the already-registered pyloric-muscle-thickness and pyloric-channel-length entries (and paed2-pylorus-caveat) are the parents; this row exists so the paediatric shelf repeats the caveat — figures are contested and must not drift
Do not invent a third thickness or length here. Overfilling and a tangential measurement manufacture stenosis.
USG · paediatric
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.