Pyloric stenosis

Key points

• Classical clinical and biochemical features are unlikely in early presentations of pyloric stenosis.
• Abdominal ultrasound may be equivocal in early presentations and should be repeated if clinical suspicion continues.
• Correcting dehydration, electrolyte disturbances and acid-base abnormalities is the priority of early management.
• Surgery can be delayed until these are corrected; normalisation of serum bicarbonate before surgery is particularly important.
• Infants with confirmed or highly suspected pyloric stenosis are transferred early to a paediatric surgical centre once an initial management plan is in place.

Overview

This Royal Children's Hospital Melbourne guideline covers the recognition and initial management of pyloric stenosis in infants. The condition is caused by hypertrophy and hyperplasia of the muscular layers of the pylorus, leading to gastric outlet obstruction; it usually presents between 2 and 6 weeks of chronological age with progressive non-bilious vomiting, is unlikely after 12 weeks of age, and is treated definitively by pyloromyotomy.

Risk factors and history

Risk factors include male sex, being first born, a parental history of pyloric stenosis (especially maternal), preterm birth, younger maternal age, postnatal exposure to macrolide antibiotics, formula feeding and maternal smoking during pregnancy. Vomiting is recurrent and progressively more forceful, may be projectile, may occur shortly after feeds and is non-bilious; it is blood-stained in less than 10%. The infant may appear hungry after vomiting and may have weight loss or inadequate weight gain.

Examination

The degree of dehydration is assessed and the infant is weighed and plotted on a growth chart. Visible gastric peristalsis may be more obvious after a feed. The pyloric mass is olive-shaped, lies in the right upper quadrant at the lateral edge of the rectus abdominis muscle and is best felt from the left side with the infant settled and supine, sometimes only after repeated examinations. Peristalsis and the mass are unlikely in early presentations and are not required to consider the diagnosis. Differential diagnoses include urinary tract infection, gastroenteritis, gastro-oesophageal reflux, surgical causes such as volvulus or malrotation, and congenital adrenal hyperplasia.

Investigations and treatment

A capillary or venous blood gas is checked for electrolytes and glucose; hypochloraemic hypokalaemic metabolic alkalosis may be seen with prolonged vomiting, in proportion to the duration of symptoms. Abdominal ultrasound is 95% sensitive. Management includes IV access, stopping oral feeds and a nasogastric tube if profuse vomiting continues. Resuscitation, when required, uses 0.9% sodium chloride; deficit and maintenance fluids use 0.9% sodium chloride with 5% glucose, with potassium added once urine output is adequate (1-2 mL/kg/hr). Surgery waits for normal bicarbonate because of the risk of postoperative hypoventilation or apnoea in metabolic alkalosis.

Frequently asked questions

Does an equivocal first ultrasound rule out pyloric stenosis?

No. Ultrasound may be equivocal early, and a repeat study should be considered if clinical suspicion continues.

Why is surgery not performed immediately?

Dehydration, electrolyte and acid-base abnormalities are corrected first; a normal serum bicarbonate reduces the risk of hypoventilation or apnoea after surgery.

When can an infant be discharged?

When ultrasound is not consistent with pyloric stenosis, differential diagnoses have been considered, the infant is clinically well and tolerating oral feeds, and a follow-up plan is in place.

Source

The Royal Children's Hospital Melbourne. Clinical Practice Guidelines: Pyloric stenosis. Last updated March 2024. Endorsed by the Paediatric Improvement Collaborative (PIC). Summary prepared by Medpresso from the original guideline; it is not a substitute for the full text or for medical advice.