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Summary Table

Category	Details
Risk Factors	Trisomy 21 (Down syndrome, present in ~30%), maternal polyhydramnios, prematurity, associated VACTERL anomalies, cardiac defects
Etiology	Failure of recanalization of the duodenal lumen during the 8th to 10th week of gestation
Patient Presentation	Newborn (first 24 to 48 hours of life) with bilious vomiting and epigastric distension; history of polyhydramnios
Classic Physical Exam	Epigastric fullness with scaphoid lower abdomen, visible gastric peristalsis, features of Down syndrome
Key Diagnostic Results	Plain abdominal X-ray showing the "double bubble" sign with absence of distal bowel gas; prenatal ultrasound showing double bubble plus polyhydramnios
Management	NPO, orogastric tube decompression, IV fluid and electrolyte correction, evaluation for associated anomalies, then surgical duodenoduodenostomy
Keywords	"Double bubble sign", "bilious vomiting in newborn", "Down syndrome plus vomiting", "polyhydramnios", "first day of life", "windsock deformity" (for type I web)

1. Pathophysiology

Duodenal atresia results from a failure of recanalization of the duodenal lumen during embryologic development. Around the 6th to 7th week of gestation, epithelial proliferation transiently obliterates the duodenal lumen (the solid cord stage). Between the 8th and 10th week, vacuolization restores the lumen. When this recanalization fails, the duodenum remains occluded at birth, producing complete obstruction (atresia) or partial obstruction (stenosis).

The obstruction is postampullary in approximately 80% of cases, meaning the blockage is distal to the entry point of the common bile duct. This is why the hallmark presentation is bilious vomiting. In the remaining 20%, the obstruction is preampullary, producing non-bilious vomiting; this preampullary subtype is more often associated with annular pancreas.

In utero, the fetus normally swallows amniotic fluid, which is absorbed through the intestines. When the duodenum is obstructed, fluid cannot be absorbed downstream, resulting in maternal polyhydramnios. After birth, swallowed air accumulates in the stomach and the dilated proximal duodenum, while the distal bowel remains gasless. This produces the classic double bubble sign with absent distal gas, the single most testable radiographic finding.

A clinically important point: roughly one-third of infants with duodenal atresia have Trisomy 21, and conversely about one-third of infants with Trisomy 21 have a gastrointestinal anomaly. This association drives the workup for cardiac and chromosomal abnormalities.

2. Classification and Clinical Manifestation

Anatomic Classification

Type	Anatomy	Notes
Type I	Intact mucosal web or membrane with intact muscularis	Most common (~90%); may produce "windsock deformity" on contrast study
Type II	Two atretic ends connected by a fibrous cord; mesentery intact	Less common
Type III	Complete separation of duodenal segments with V-shaped mesenteric defect	Least common; may have associated vascular anomalies

Classification by Location Relative to the Ampulla of Vater

Location	Frequency	Vomiting Type
Postampullary (distal to ampulla)	~80%	Bilious (green)
Preampullary (proximal to ampulla)	~20%	Non-bilious (clear or milky)

Clinical Manifestations

Feature	Description
Vomiting onset	Within first 24 to 48 hours of life
Vomiting character	Bilious in most cases; non-bilious if preampullary
Abdominal exam	Epigastric distension with scaphoid lower abdomen
Stool	Delayed or absent meconium passage in many cases (though some pass meconium normally)
Dysmorphic features	Down syndrome features (flat facies, epicanthal folds, single palmar crease) in ~30%
Prenatal clue	Polyhydramnios on maternal ultrasound, often with visible double bubble

3. Diagnostic Workup

Test	Role	Key Finding
Maternal prenatal ultrasound	Prenatal screening	Polyhydramnios plus fetal double bubble
Plain abdominal X-ray (upright or supine)	Best initial test postnatally	Double bubble sign with no distal gas
Upper GI contrast study	Used when X-ray is atypical or when malrotation must be excluded	Confirms level of obstruction; "windsock" in type I
Echocardiography	Workup for associated anomalies	Detects cardiac defects (especially with Down syndrome)
Karyotype	Confirm Trisomy 21 if features present	Detects chromosomal abnormality
Renal ultrasound and spinal imaging	Workup for VACTERL association	Detects associated anomalies

The diagnosis often begins before birth. Maternal ultrasound in the second or third trimester may reveal polyhydramnios along with a fetal double bubble, prompting referral for delivery at a center with pediatric surgical capability.

After birth, when a newborn presents with bilious vomiting in the first day of life, the best initial test is a plain abdominal X-ray. The pathognomonic finding is the double bubble sign: a large gastric air bubble paired with a smaller duodenal air bubble, with no air distal to the obstruction. The absence of distal gas is the discriminator that distinguishes atresia from stenosis (where distal gas is preserved) and from malrotation (where gas may be present distally in variable patterns).

In a classic case (newborn with bilious vomiting, X-ray showing double bubble and a gasless abdomen distal to the duodenum), no further imaging is required, and the X-ray itself functions as the confirmatory test. If the X-ray is equivocal, or if there is any concern for malrotation with midgut volvulus, an upper GI contrast study is performed urgently. This is the closest thing to a gold standard when imaging is ambiguous, as it identifies the level of obstruction and rules out malrotation.

Because of the strong association with Trisomy 21 and other anomalies, every infant with confirmed duodenal atresia requires:

Echocardiography to evaluate for congenital heart disease
Karyotype if dysmorphic features are present
Evaluation for VACTERL association (vertebral, anal, cardiac, tracheo-esophageal, renal, limb anomalies)

4. Management and Treatment

Phase	Intervention	Purpose
Initial stabilization	NPO	Stop further intake
Initial stabilization	Orogastric/nasogastric tube decompression (10 Fr sump)	Decompress stomach, prevent aspiration
Initial stabilization	IV fluid resuscitation with electrolyte correction	Treat dehydration and metabolic alkalosis
Initial stabilization	Workup for associated anomalies	Identify cardiac, chromosomal, VACTERL findings
Definitive surgery	Duodenoduodenostomy (often diamond-shaped, Kimura technique)	Bypass the atretic segment
Postoperative care	Gradual enteral feed advancement, parenteral nutrition as needed	Allow anastomosis healing and motility recovery

Acute stabilization comes first. The infant is kept NPO, and an orogastric or nasogastric sump tube is placed for continuous decompression. This prevents aspiration and reduces gastric distension. IV fluid resuscitation corrects the dehydration and the hypochloremic, hypokalemic metabolic alkalosis that develops from persistent vomiting. Maintenance fluids in the neonate are typically dextrose-containing isotonic solutions, with potassium added once urine output is established.

Before surgery, the team evaluates for associated anomalies, since these influence anesthetic risk and timing. Echocardiography is mandatory because cardiac lesions in a Down syndrome infant change perioperative management.

Definitive treatment is surgical. The standard procedure is a duodenoduodenostomy, most often performed using a diamond-shaped anastomosis (Kimura technique), which connects the proximal dilated duodenum to the distal collapsed segment. This can be done open or laparoscopically. If a duodenal web (type I) is identified, web excision with duodenoplasty may be feasible. Duodenojejunostomy is a fallback when local anatomy precludes duodenoduodenostomy.

The next best step in management for a stable newborn with confirmed duodenal atresia is not immediate emergent surgery but rather decompression, fluid resuscitation, and workup for associated anomalies, followed by surgical correction within the first one to two days of life. Duodenal atresia is not a surgical emergency in the same sense as midgut volvulus, because there is no risk of vascular compromise. This distinction is high-yield.

Postoperatively, feeding is advanced gradually because the chronically dilated proximal duodenum has poor motility and may take days to weeks to function normally. Parenteral nutrition is often required during this transition.

Contraindications and considerations: There are no absolute contraindications to repair, but anesthetic risk is elevated in infants with significant cardiac defects, and surgery may need to be coordinated with cardiology. Prematurity and very low birth weight may warrant temporary delay until the infant is stable.

5. Differential Diagnosis and Distractors

Differential	Why It's Similar	Key Discriminator
Malrotation with midgut volvulus	Bilious vomiting in a newborn; the most dangerous mimic	Distal bowel gas may be present; X-ray often non-diagnostic; upper GI shows corkscrew or right-sided duodenum; this is a true surgical emergency requiring rapid diagnosis to prevent bowel necrosis
Jejunal or ileal atresia	Bilious vomiting, neonatal obstruction	X-ray shows multiple dilated loops with air-fluid levels, not a clean double bubble; obstruction is more distal
Annular pancreas	Identical clinical and radiographic picture (also produces double bubble); often coexists with duodenal atresia	Distinguished at surgery; preampullary obstruction more common, so vomiting may be non-bilious
Duodenal stenosis or web	Same anatomic region, similar presentation but partial	Distal gas is present on X-ray; presentation may be delayed beyond the neonatal period
Pyloric stenosis	Vomiting in early infancy	Non-bilious projectile vomiting at 3 to 6 weeks of age, not in the newborn period; palpable olive in epigastrium; ultrasound shows pyloric muscle thickening
Hirschsprung disease	Neonatal obstruction with delayed meconium	Distal obstruction pattern; distended abdomen rather than epigastric only; rectal exam produces explosive stool; contrast enema shows transition zone
Tracheoesophageal fistula or esophageal atresia	Drooling, choking with feeds in the newborn	NG tube cannot pass into the stomach; coiled tube on X-ray

6. Traps and High-Yield Pearls

The single most important trap is the bilious vomiting in a newborn rule: assume malrotation with midgut volvulus until proven otherwise, because volvulus can necrose the entire midgut within hours. Even when the double bubble sign is present and the diagnosis appears to be duodenal atresia, an upper GI contrast study should be obtained if there is any distal bowel gas or any atypical feature, since malrotation can produce a similar picture. Test writers exploit this by giving a vignette with bilious vomiting and asking for the next best step; the correct answer often emphasizes ruling out volvulus before assuming a benign atresia.

A second trap is the double bubble sign itself. While classic for duodenal atresia, it can also be produced by annular pancreas, duodenal web, malrotation with Ladd bands, and even midgut volvulus. The discriminator is whether distal gas is present: a completely gasless abdomen distal to the second bubble strongly favors atresia, while distal gas should raise suspicion for stenosis, web, or malrotation.

A third trap is forgetting the associated anomalies. A vignette featuring a newborn with bilious vomiting, a flat facial profile, and an abnormal cardiac exam is asking you to recognize Trisomy 21 plus duodenal atresia plus AV septal defect. Missing the cardiac evaluation before surgery is a testable management error.

A fourth pearl is timing: duodenal atresia is urgent but not emergent. The infant should be stabilized, evaluated, and operated on within the first one to two days, not immediately rushed to the operating room. Contrast this with midgut volvulus, where any delay risks bowel loss.

The core competencies being tested are: recognizing the classic radiographic and clinical pattern, distinguishing atresia from the lethal volvulus mimic, sequencing the workup correctly (X-ray first, contrast study if atypical, echocardiography before surgery), and anticipating associated conditions (Trisomy 21, cardiac defects, VACTERL). Mastery of these four threads is what separates the right answer from a plausible distractor.

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