A 4‑week‑old male infant is brought to the emergency department by his parents for a 1‑week history of progressively worsening, forceful vomiting that occurs after every feed. They describe the vomit as non‑bilious. They note the baby is increasingly fussy and seems hungry immediately after vomiting. The prenatal course and delivery were uneventful, and he had been doing well until 1 week ago. On physical examination, the infant appears mildly dehydrated. A small, firm, mobile mass is felt in the right upper abdomen. Laboratory results show a metabolic alkalosis.
Which of the following s the most appropriate next step in managing this patient?
The correct answer is:
D) Perform an abdominal ultrasound
The classic picture of hypertrophic pyloric stenosis (HPS) is projectile, non‑bilious vomiting in a 2–6‑week‑old with a palpable “olive,” in the abdomen plus a hypochloremic, hypokalemic metabolic alkalosis in more advanced cases. Ultrasound is the diagnostic test of choice, with typical criteria including pyloric muscle thickness ≥3–4 mm and channel length ≥14–18 mm. Initial management is intravenous fluid and electrolyte resuscitation, followed by pyloromyotomy once the laboratory abnormalities are corrected.
Answer choice A: Begin erythromycin therapy, is incorrect. Macrolides such as erythromycin can actually increase risk of HPS when used postnatally. They are not therapy for HPS.
Answer choice B: Initiate thickened feeds, is incorrect. Initiating feeds are appropriate for reflux but not for the fixed gastric outlet obstruction seen in HPS.
Answer choice C: Order an abdominal X-ray, is incorrect. Plain films are nonspecific, and ultrasound is far more sensitive and specific and is the recommended initial test.
Answer choice E: Proceed directly to pyloromyotomy, is incorrect. Fluid resuscitation and correction of electrolyte abnormalities and acid‑base status should precede surgery. Ultrasound confirmation is standard.
Key Learning Point
In suspected HPS, obtain an abdominal ultrasound to confirm the diagnosis, correct dehydration and electrolyte abnormalities, and then perform pyloromyotomy.
