STEPTRACKERGASTROINTESTINAL | PATHOLOGY + EMBRYOLOGY | HIGH-YIELD REVIEW

Pediatric GI

Congenital and neonatal GI disease — sorted by the color of the vomit, the timing of the stool and the shape of the gas.

FOCUS ON
Nonbilious projectile vomiting at 2–6 weeks = pyloric stenosis (olive mass, hypochloremic hypokalemic alkalosis). Bilious vomiting = obstruction beyond the ampulla (duodenal atresia, malrotation). No meconium in 48 hours = Hirschsprung or meconium ileus (CF). Premature + formula + pneumatosis = NEC.
DISORDER
MECHANISM
FEATURES
CLUE · DIAGNOSIS
Hypertrophic pyloric stenosis
Hypertrophy of pyloric muscle; first-born males; early macrolide exposure
Nonbilious projectile vomiting at 2–6 weeks; palpable olive; visible peristalsis; hungry after vomiting
Hypochloremic hypokalemic metabolic alkalosis · ultrasound · pyloromyotomy
Duodenal atresia
Failure of duodenal recanalization
Bilious vomiting in the first day; polyhydramnios
Double bubble · Down syndrome
Jejunal / ileal atresia
In-utero vascular accident (vasoconstrictors: cocaine, smoking)
Bilious vomiting, distension; "apple peel" atresia
Triple bubble / multiple dilated loops
Malrotation
Abnormal midgut rotation; Ladd bands cross the duodenum; narrow mesentery
Bilious vomiting; midgut volvulus → ischemia
Upper GI series: duodenojejunal junction on the right, corkscrew · surgical emergency
Hirschsprung disease
Failed neural crest migration → no Meissner/Auerbach plexus in distal colon; RET mutation; Down syndrome
No meconium in 48 h, distension, chronic constipation; empty rectum, explosive stool after rectal exam
Rectal suction biopsy: no ganglion cells · resection
Meconium ileus
Thick meconium from CF (CFTR) obstructs the ileum
Failure to pass meconium, distension, bilious vomiting
"Soap bubble" appearance; few air-fluid levels · first sign of CF
Necrotizing enterocolitis
Immature gut + formula feeding + bacteria → ischemic necrosis
Premature infant: feeding intolerance, distension, bloody stool; terminal ileum and colon
Pneumatosis intestinalis, portal venous gas
Gastroschisis
Abdominal wall defect, usually right of the umbilicus; no membrane
Bowel exposed to amniotic fluid; rarely other anomalies
↑ maternal AFP
Omphalocele
Failure of gut to return after physiologic herniation; midline; covered by peritoneum + amnion
Often with other anomalies
Trisomy 13 and 18, Beckwith-Wiedemann · ↑ AFP
Congenital diaphragmatic hernia
Defective pleuroperitoneal membrane; left posterolateral (Bochdalek)
Respiratory distress at birth, scaphoid abdomen, bowel sounds in chest
Pulmonary hypoplasia determines prognosis
Annular pancreas
Ventral pancreatic bud encircles the 2nd part of the duodenum
Duodenal obstruction, bilious vomiting
Down syndrome

Mechanism — pyloric stenosis alkalosis

Vomit HCl
→
↓ Cl⁻, ↑ HCO₃⁻
→
Volume loss→ RAAS ↑
→
AldosteroneK⁺ and H⁺ wasted in urine
→
Hypokalemic alkalosisParadoxical aciduria

Correct fluid and electrolytes (saline + KCl) before the pyloromyotomy.

The vomiting neonate

CLUE
LEVEL
THINK
Nonbilious, 2–6 weeks
Pylorus
Pyloric stenosis
Bilious, day 1, double bubble
Duodenum
Atresia, annular pancreas
Bilious, sudden, sick infant
Midgut
Malrotation + volvulus
Bilious + many dilated loops
Jejunum / ileum
Atresia, meconium ileus
Delayed meconium, distension
Colon
Hirschsprung
Drooling, choking at first feed
Esophagus
Atresia ± TEF

How it's tested

COMMON CONFUSIONGastroschisis: right of the umbilicus, no sac, usually isolated. Omphalocele: midline, covered by a sac, often with trisomy or Beckwith-Wiedemann.
THE TRAPHirschsprung is diagnosed by the absence of ganglion cells on biopsy, not by barium enema. The aganglionic narrow segment is the abnormal one, not the dilated part above it.
YOUR APPROACHAge + bilious or not + meconium timing + imaging sign (olive, double bubble, pneumatosis) → level of the lesion → embryologic cause.

If you see… think…

3-week-old boy, projectile nonbilious vomiting, olive mass → pyloric stenosis
Pyloric stenosis labs → hypochloremic hypokalemic metabolic alkalosis
Newborn with Down syndrome, bilious vomiting, double bubble → duodenal atresia
Sudden bilious vomiting in a healthy infant → malrotation with volvulus
No meconium at 48 h, explosive stool on rectal exam → Hirschsprung disease
Meconium ileus → cystic fibrosis
Premature formula-fed infant, bloody stool, pneumatosis → NEC
Bowel outside the abdomen to the right of the cord, no sac → gastroschisis
Midline sac with liver and bowel + macroglossia → omphalocele (Beckwith-Wiedemann)
Respiratory distress, scaphoid abdomen, bowel in left chest → Bochdalek hernia