A G1P1 mother brings in her 1 month old newborn male because he is "always hungry." When you ask further, it turns out he has been having projectile nonbilious vomiting immediately after he eats, and then after the vomiting, appears to be hungry again. Right before he vomits, the mother notes quivering waves on his belly. The mother has been breastfeeding him frequently.
On exam, you note a dehydrated infant. On the abdominal exam, right upper quadrant, you appear to feel one of these at the lateral edge of the rectus abdominus muscle:
Here's a barium study:
"Oh my God," the mother says. "Is it cancer?"
Challenge: The diagnosis is easy, but what electrolyte findings do you expect in this condition?
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