Oral Board Case: Pyloric Stenosis

What is your differential diagnosis for a 3-week-old with projectile vomiting, and what features point you toward pyloric stenosis?

Expected answer

Differential includes hypertrophic pyloric stenosis, gastroesophageal reflux/overfeeding, malrotation with midgut volvulus, gastroenteritis, milk protein allergy, and metabolic/adrenal disease. The key discriminator is that pyloric stenosis produces NON-bilious, progressively projectile emesis in a hungry infant 2–8 weeks old, often with a palpable 'olive' and visible peristalsis. Critically, bilious emesis would demand emergent evaluation for malrotation/volvulus, which is a true surgical emergency.

How do you confirm the diagnosis?

Expected answer

The diagnosis can be clinical if a firm olive is palpated in a relaxed infant (present in ~72–89%). If the exam is equivocal, obtain an abdominal ultrasound. Diagnostic findings are pyloric muscle wall thickness ≥4 mm and pyloric channel length ≥16 mm. An upper GI series is an alternative and also helps exclude malrotation if the diagnosis is uncertain.

What laboratory abnormalities do you expect and why?

Expected answer

The classic derangement is a hypokalemic, hypochloremic metabolic alkalosis from loss of gastric HCl and potassium in the vomitus. There is often decreased urine output and a paradoxical aciduria—the kidneys excrete H+ to preserve sodium/volume despite systemic alkalosis. Severity is graded by bicarbonate: slight <25, moderate 26–35, severe >35 mEq/L.

Is this a surgical emergency? What is your immediate priority?

Expected answer

No—pyloric stenosis is a medical emergency of fluid and electrolyte derangement, not a surgical emergency. The priority is resuscitation and correction of dehydration and electrolytes BEFORE the OR. Operating on an alkalotic, dehydrated infant risks postoperative apnea and difficulty weaning from the ventilator due to alkalosis-driven hypoventilation.

Describe your resuscitation plan.

Expected answer

Stop enteral feeds. Give a normal saline bolus of 20 cc/kg for volume, then continuous IV fluids of D5 ½NS with 20–30 mEq KCl/L at 1.25–2x maintenance until urine output reaches ~1 cc/kg/hr. Potassium should not be withheld waiting for urine output as older teaching suggested—replace it once you have monitoring in place. Monitor urine output and recheck the BMP every 6–8 hours until electrolytes normalize. A nasogastric tube is not mandatory but may be used in severe cases.

What specific endpoints tell you the infant is ready for the operating room?

Expected answer

The infant is resuscitated when the metabolic alkalosis is corrected: CO2/bicarbonate <30 mEq/L, chloride >100, and potassium >4, with adequate urine output. Only then should pyloromyotomy proceed.

Describe the operative approach and the key intraoperative steps.

Expected answer

Pyloromyotomy (Ramstedt) can be open or laparoscopic. Open uses a RUQ transverse or supraumbilical incision; laparoscopic uses an umbilical camera port with two lateral working stabs. The hypertrophied pylorus is delivered/visualized, a seromuscular incision is made along the anterior avascular plane from the pyloric vein of Mayo proximally onto the antrum, and the muscle fibers are spread bluntly down to the submucosa, allowing the mucosa to bulge. The muscle must be split completely to relieve obstruction.

How do you check for and manage a mucosal perforation intraoperatively?

Expected answer

After completing the myotomy, insufflate air through the NG/OG tube while observing the myotomy site for bubbles or leak of gastric contents; watch for bilious/mucosal fluid. If a perforation is identified, repair it primarily with fine absorbable suture and, if needed, rotate and perform a new myotomy 90–180 degrees away from the original site. Recognizing perforation at the table is essential—missed perforation leads to peritonitis and sepsis.

How do you feed the infant postoperatively, and how do you counsel the family about vomiting?

Expected answer

Two accepted strategies exist with no meaningful difference in length of stay: an ad lib schedule (more emesis but faster to full feeds) or a regimented schedule starting with Pedialyte and advancing formula/breast milk every few hours. Some postoperative emesis is common and usually self-limited due to residual gastric edema/dysmotility; persistent vomiting beyond several days should prompt concern for an incomplete myotomy.