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Ultrasound Pylorus (Pediatric Hypertrophic Pyloric Stenosis)

USNo contrastPediatric

Indications

Non-bilious projectile vomiting in infant (typically 2-8 weeks)
Palpable olive
Suspected gastric outlet obstruction

Patient prep

Recently fed/with stomach containing fluid can help; avoid overdistension
Supine or right lateral decubitus to bring antrum/pylorus into view

Contrast

None / non-contrast

Technique

High-frequency linear transducer 7-15 MHz
Identify pylorus to the right of midline, posterior to gallbladder/inferior to liver edge
Real-time observation of gastric emptying / fluid passage through channel
Reposition (RLD) and give oral fluid to fill antrum as needed

Series / Sequences

#	Series / Sequence	Plane	Notes
1	Pylorus long axis	Long axis	Measure pyloric CHANNEL/canal LENGTH (abnormal >15-16 mm)
2	Pylorus transverse	Transverse	Single muscle WALL THICKNESS (abnormal >3 mm); transverse diameter
3	Real-time gastric emptying	Long axis	Lack of fluid passage / hyperperistalsis against closed channel

Key points

Diagnostic thresholds: single muscle wall thickness >3 mm and pyloric channel length >15-16 mm (the 'pi' mnemonic 3.14...)
Look for non-relaxing, elongated channel with failure of gastric contents to pass in real time
Target sign (hypertrophied hypoechoic muscle around echogenic mucosa) on transverse
Measure muscle wall, not including mucosa; borderline values warrant re-evaluation

References

• AIUM Practice Parameter for the Performance of an Ultrasound Examination of the Abdomen (pediatric)
• ACR Appropriateness Criteria: Vomiting in Infants
• Radiopaedia: Hypertrophic pyloric stenosis link

Source: Researched — verify against your institution

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Reference template — verify and adapt to your scanner, vendor and institution before clinical use. Not a substitute for clinical judgment.