A 42-year-old woman presents to the emergency department in active labor. She has had no prenatal care and is unsure of the gestational age. Labor progresses rapidly and spontaneous vaginal delivery of a baby boy occurs 3 hours after presentation. On initial exam, the child is 1.9 kg (4.2 lb) with a small head and jaw. A sac-like structure containing intestine, as can be seen in the picture, protrudes from the abdominal wall. What complication is closely associated with this presentation?

Dehydration and necrosis of bowel

Twisting of the bowel around itself

A new mother expresses her concerns because her 1-day-old newborn has been having feeding difficulties. The child vomits after every feeding and has had a continuous cough since shortly after birth. The mother denies any greenish coloration of the vomit and says that it is only composed of whitish milk that the baby just had. The child exhibits these coughing spells during the exam, at which time the physician notices the child’s skin becoming cyanotic. The mother states that the child was born vaginally with no complications, although her records show that she had polyhydramnios during her last ultrasound before the delivery. Which of the following is the most likely cause of the patient’s symptoms?

Defective formation of the esophagus with tracheoesophageal connection

Failure of recanalization of duodenum

Obstruction due to failure of rotation of pancreatic tissue

Hypertrophy of the pyloric sphincter

Failure of neural crest cells to migrate into the myenteric plexus

A 5-week-old male infant is brought to the physician by his mother because of a 4-day history of recurrent nonbilious vomiting after feeding. He was born at 36 weeks' gestation via spontaneous vaginal delivery. Vital signs are within normal limits. Physical examination shows a 2-cm epigastric mass. Further diagnostic evaluation of this patient is most likely to show which of the following?

Elongated and thickened pylorus on abdominal ultrasound

Dilated colon segment on abdominal x-ray

Double bubble sign on abdominal x-ray

High serum 17-hydroxyprogesterone concentration

Corkscrew sign on upper gastrointestinal contrast series

A 3-week-old firstborn baby girl is brought to the pediatric emergency room with projectile vomiting. She started vomiting while feeding 12 hours ago and has been unable to keep anything down since then. After vomiting, she appears well and hungry, attempting to feed again. The vomitus has been non-bloody and non-bilious. The last wet diaper was 10 hours ago. The child was born at 40 weeks gestation to a healthy mother. On examination, the child appears sleepy but has a healthy cry during the exam. The child has dry mucous membranes and delayed capillary refill. There is a palpable olive-shaped epigastric mass on palpation. Which of the following is the most likely cause of this patient's condition?

Hypertrophic muscularis externa

Failure of neural crest cell migration into the rectum

Telescoping of the small bowel into the large bowel

Patent tract between the trachea and esophagus

Failure of duodenal lumen recanalization

A 2-week-old boy has developed bilious vomiting. He was born via cesarean section at term. On physical exam, his pulse is 140, blood pressure is 80/50 mmHg, and respirations are 40/min. His abdomen appears distended and appears diffusely tender to palpation. Abdominal imaging is obtained (Figures A). Which of the following describes the mechanism that caused this child's disorder?

Abnormal rotation of the midgut

Ischemia-reperfusion injury in premature neonate

Partial absence of ganglion cells in large intestine

A 26-year-old G1P0 mother is in the delivery room in labor. Her unborn fetus is known to have a patent urachus. Which of the following abnormalities would you expect to observe in the infant?

Meconium discharge from umbilicus

A 4-year-old girl is brought to the emergency department by her parents with a sudden onset of breathlessness. She has been having similar episodes over the past few months with a progressive increase in frequency over the past week. They have noticed that the difficulty in breathing is more prominent during the day when she plays in the garden with her siblings. She gets better once she comes indoors. During the episodes, she complains of an inability to breathe and her parents say that she is gasping for breath. Sometimes they hear a noisy wheeze while she breathes. The breathlessness does not disrupt her sleep. On examination, she seems to be in distress with noticeable intercostal retractions. Auscultation reveals a slight expiratory wheeze. According to her history and physical findings, which of the following mechanisms is most likely responsible for this child’s difficulty in breathing?

Airway hyperreactivity to external allergens causing intermittent airway obstruction

Defective chloride channel function leading to mucus plugging

Chronic mucus plugging and inflammation leading to impaired mucociliary clearance

Inflammation leading to permanent dilation and destruction of alveoli

Destruction of the elastic layers of bronchial walls leading to abnormal dilation

Gastrointestinal malformations for USMLE Step 1: High-Yield Pediatrics Lessons

Esophagus & Diaphragm - Upper Tract Troubles

Tracheoesophageal Fistula (TEF)
- Most common: Type C (85%), with esophageal atresia & distal fistula.
- Antenatal: Polyhydramnios (impaired fetal swallowing).
- Postnatal: Frothing/drooling, choking on feeds, respiratory distress.
- Diagnosis: Coiled nasogastric tube in upper esophagus on X-ray.
- 📌 VACTERL association: Vertebral, Anal, Cardiac, TEF, Renal, Limb defects.
Congenital Diaphragmatic Hernia (CDH)
- Most common: Bochdalek hernia (left posterolateral).
- Signs: Severe respiratory distress at birth, scaphoid abdomen, bowel sounds in chest.
- Management: Immediate intubation; avoid bag-mask ventilation.

⭐ CDH Prognosis: The Lung-to-Head Ratio (LHR) on fetal ultrasound is the best predictor of outcome.

Congenital Diaphragmatic Hernia: Development and Anomalies

Gut Obstructions - The Vomiting Babies

Presents with non-bilious or bilious vomiting, depending on obstruction level relative to the ampulla of Vater.
Key diagnostic: Abdominal X-ray to identify characteristic gas patterns.

Feature	Hypertrophic Pyloric Stenosis (HPS)	Duodenal Atresia	Jejunal/Ileal Atresia
Vomiting	Non-bilious, projectile (2-8 wks)	Bilious (hours post-birth)	Bilious (24-48 hrs)
Palpation	Olive-shaped mass in RUQ	Scaphoid abdomen	Abdominal distension
X-ray Sign	Single bubble (dilated stomach)	Double bubble	Triple bubble / multiple levels
Cause	Pylorus muscle hypertrophy	Failure to recanalize	In utero vascular accident

⭐ Double Bubble Sign: The pathognomonic "double bubble" on an AXR for duodenal atresia is caused by gas in the stomach and the proximal duodenum. It is strongly associated with Trisomy 21.

Twists & Nerves - Gut's Wrong Turn

Malrotation: Abnormal intestinal rotation during fetal life, creating a narrow mesenteric base prone to twisting (volvulus).
- Presentation: Sudden onset of bilious vomiting in a neonate is the cardinal sign.
- Diagnosis: Upper GI contrast series is the gold standard, showing a "corkscrew" sign. USG may show a "whirlpool sign".
- Management: Emergency surgery (Ladd's Procedure).
Hirschsprung's Disease: Aganglionosis of the distal bowel due to failed neural crest cell migration.
- Presentation: Failure to pass meconium in the first 24-48 hours, abdominal distension, and bilious emesis.
- Diagnosis: Rectal suction biopsy is the definitive diagnostic test.

⭐ In Hirschsprung's disease, the transition zone is most commonly found in the recto-sigmoid segment (~80%).

Anorectal Malformations - The Final Exit

Spectrum of hindgut termination anomalies, often part of the VACTERL association (Vertebral, Anal, Cardiac, Tracheal, Esophageal, Renal, Limb).
Classification: High vs. Low, based on the relation of the rectal pouch to the pubococcygeal (PC) line.
Diagnosis: Clinical exam + Invertogram (Wangesteen-Rice) to assess pouch height. A gas-to-skin distance > 2 cm indicates a high lesion.

⭐ In males, the most common fistula is rectourethral (bulbar). In females, it's rectovestibular.

Anorectal malformations and fistulas in females and males

Management: Low lesions are treated with perineal anoplasty. High lesions require a staged approach: initial colostomy, followed by Posterior Sagittal Anorectoplasty (PSARP).

High‑Yield Points - ⚡ Biggest Takeaways

Tracheoesophageal fistula is most commonly Type C; presents with coiling of the nasogastric tube.

Duodenal atresia shows a "double-bubble" sign on X-ray and is strongly associated with Down syndrome.

Jejunal and ileal atresia are due to an in-utero vascular accident.

Hypertrophic pyloric stenosis presents with non-bilious projectile vomiting and a palpable "olive-like" mass.

Hirschsprung's disease results from failed neural crest cell migration; diagnosis is confirmed by rectal biopsy.

Meckel's diverticulum is diagnosed using a Technetium-99m scan for ectopic gastric mucosa.

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