Pediatric GI: Pyloric Stenosis, Intussusception & Hirschsprung
A board-focused walkthrough of the three classic pediatric surgical GI conditions — pyloric stenosis, intussusception, and Hirschsprung disease — organized by buzzword vignette, best diagnostic test, and the tested next-best-step in management. Emphasizes the high-yield trap of operating before resuscitation or enema reduction.
Three Surgical Bellies, Sorted by Age and Vomit Color
Three surgical causes of infant vomiting and obstruction dominate the boards, and the exam sorts them by age and vomit color. Pyloric stenosis hits the 3–6 week firstborn male with nonbilious projectile vomiting. Intussusception strikes 6 months–2 years with colicky pain and late currant-jelly stool. Hirschsprung disease presents in the neonate who fails to pass meconium within 48 hours.
For each, the tested chain is identical: recognize the buzzword vignette → order the right imaging → choose the definitive step. The single most repeated distractor is jumping to surgery too early — before the pyloric-stenosis infant is resuscitated, or before an intussusception enema is attempted. Master those decision points and this whole cluster becomes free points.
- Who: firstborn male, 3–6 wks old (range 2–12 wks); risk ↑ with early macrolides (esp. erythromycin; azithromycin), bottle-feeding, maternal smoking
- Presentation: nonbilious projectile vomiting right after feeds; infant is hungry again immediately ("hungry vomiter"); palpable firm "olive" in the epigastrium/RUQ; visible peristaltic waves
- Labs: hypochloremic, hypokalemic metabolic alkalosis (vomiting HCl); late paradoxical aciduria (kidney trades H⁺ to retain Na⁺/volume)
- Dx: ultrasound (first-line) — pyloric muscle wall ≥3 mm thick and channel ≥14 mm long; upper-GI/barium shows the "string sign"
- Mgmt: correct fluids/electrolytes FIRST (isotonic saline; add K⁺ once the infant is voiding), then Ramstedt pyloromyotomy — surgery is never emergent
A 5-week-old firstborn boy has 1 week of worsening vomiting that now shoots across the room, is non-bilious, and he roots to feed again right after each episode. A firm, mobile mass is felt in the epigastrium. Labs: pH 7.51, Cl⁻ 88, K⁺ 3.0.
- Diagnosis: hypertrophic pyloric stenosis (hypochloremic hypokalemic metabolic alkalosis).
- Best initial test: abdominal ultrasound.
- NEXT BEST STEP: IV isotonic saline to restore volume, then replace potassium once he is making urine — not the OR. Pyloromyotomy proceeds only after electrolytes and pH normalize, because uncorrected metabolic alkalosis blunts the respiratory drive and raises the risk of post-operative apnea under anesthesia.
- Who: 6 mo–2 yr; most common cause of bowel obstruction in this age; ileocolic most common
- Lead point: usually idiopathic — lymphoid hyperplasia (Peyer patches) after a viral illness (e.g., adenovirus). Older/atypical child → Meckel diverticulum (most common pathologic lead point), HSP (IgA vasculitis), lymphoma, polyp
- Classic triad (all three in a minority): intermittent colicky pain (draws knees up, calm between attacks) + palpable "sausage-shaped" RUQ mass + "currant-jelly" stool (blood + mucus, a late finding). Vomiting is common; may present as isolated lethargy
- Dx: ultrasound — "target"/"donut" sign, pseudokidney sign
- Mgmt: air (pneumatic) or contrast enema is both diagnostic AND therapeutic (reduces it); go to surgery if the enema fails or if there is peritonitis, perforation, or shock (which also contraindicate the enema)
A 9-month-old has episodes of drawing his legs up and screaming every 15–20 minutes, appearing well between attacks, with two episodes of vomiting. A sausage-shaped mass is palpable in the RUQ, and a diaper shows red, mucoid ("currant-jelly") stool. He is afebrile with a soft, nontender abdomen and no peritoneal signs.
- Diagnosis: ileocolic intussusception.
- Best test / next step: ultrasound (target sign) → then air or contrast enema, which is both diagnostic and therapeutic (reduction).
- Go straight to surgery instead if there is perforation, peritonitis, or shock, or if enema reduction fails.
- Cause: failed neural-crest cell migration → absent ganglion cells (Meissner + Auerbach plexuses) beginning at the rectum and extending proximally (continuous, no skip areas); RET proto-oncogene mutations
- Association: Down syndrome (trisomy 21)
- Presentation: neonate fails to pass meconium within 48 h, bilious vomiting, abdominal distension; older child → chronic constipation, failure to thrive
- Exam: tight, empty rectum with explosive expulsion of stool/gas on finger withdrawal ("squirt sign")
- Feared complication: Hirschsprung-associated enterocolitis — fever, explosive foul diarrhea, sepsis (leading cause of death)
- Dx: contrast enema shows a transition zone; anorectal manometry → failure of internal-sphincter relaxation (absent RAIR); GOLD STANDARD = rectal suction biopsy (absent ganglia, hypertrophied nerve trunks, ↑ acetylcholinesterase)
- Mgmt: surgical pull-through resection of the aganglionic segment
Bilious (green) vomiting in a neonate signals obstruction at or DISTAL to the ampulla of Vater until proven otherwise — a surgical emergency.
- Non-bilious projectile emesis → pyloric stenosis (block is proximal to where bile enters)
- Bilious emesis → think malrotation with midgut volvulus (must exclude first), intestinal atresia, and Hirschsprung (all at/distal to the ampulla)
- A newborn with bilious vomiting always warrants urgent imaging — an upper-GI series to rule out malrotation/volvulus before the bowel infarcts.
Rapid Comparison
| Feature | Pyloric Stenosis | Intussusception | Hirschsprung |
|---|---|---|---|
| Typical age | 3–6 wks | 6 mo–2 yr | Neonate (no meconium <48 h) |
| Hallmark | Nonbilious projectile vomit | Colicky pain + currant-jelly stool | Failure to pass meconium |
| Exam clue | "Olive" mass, peristaltic waves | "Sausage" mass, draws up legs | Empty rectum, "squirt sign" |
| Labs/assoc. | Hypochloremic hypokalemic alkalosis | Post-viral; Meckel/HSP lead points | Trisomy 21, RET mutation |
| Best test | Ultrasound (barium "string sign") | Ultrasound "target" sign | Rectal suction biopsy (gold) |
| Definitive Rx | Fluids first → pyloromyotomy | Air/contrast enema (→ surgery) | Pull-through resection |
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