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transposition of great arteries chest X-ray egg on string infant
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Answer: D) Transposition of Great Arteries (TGA)
X-ray Findings That Clinch the Diagnosis
The chest X-ray shows the classic "egg on a string" (egg on its side) appearance:
- Narrow superior mediastinum - because in TGA, the aorta lies directly anterior to the pulmonary artery (rather than side by side), creating a narrow vascular pedicle that looks like a "string"
- Oval/egg-shaped cardiac silhouette - mildly enlarged, globular heart
- Increased pulmonary vascular markings - reflecting increased pulmonary blood flow
Clinical Correlation
| Feature | This case |
|---|---|
| Age | 2-month-old infant |
| Cyanosis | Present (central, from birth) |
| Tachypnea/rapid breathing | Present |
| Failure to thrive | Present |
| X-ray pattern | Egg on a string + narrow mediastinum |
Why Not the Others?
| Option | X-ray Appearance | Why Excluded |
|---|---|---|
| A) Truncus arteriosus | Cardiomegaly + increased pulmonary markings, but wide mediastinum (single large vessel) | Wide, not narrow mediastinum |
| B) TAPVC (Total Anomalous Pulmonary Venous Connection) | "Snowman" or figure-of-8 heart (supracardiac type) | Different silhouette pattern |
| C) Tricuspid atresia | Small right heart, decreased pulmonary markings, left axis deviation on ECG | Oligemic (dark) lung fields, not plethoric |
| D) TGA | Egg-on-string, narrow mediastinum, increased pulmonary markings | Matches perfectly |
Pathophysiology (TGA)
In d-TGA, the aorta arises from the right ventricle and the pulmonary artery from the left ventricle, creating two parallel, non-communicating circuits. Survival depends on mixing via ASD, VSD, or PDA. Cyanosis is present from birth due to deoxygenated blood recirculating systemically. - Harrison's Principles of Internal Medicine 22E, Fig. 289-9
Management: Prostaglandin E1 to keep the ductus open + emergent balloon atrial septostomy (Rashkind procedure) to increase mixing, followed by definitive arterial switch operation (Jatene procedure).
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Seen with which condition
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TAPVC supracardiac snowman figure of 8 chest X-ray
Snowman Sign = Total Anomalous Pulmonary Venous Connection (TAPVC) - Supracardiac Type
What You See on This X-ray
The chest X-ray shows the classic "snowman" or "figure-of-8" cardiac silhouette:
- Upper circle (head of snowman) - dilated vertical vein + left brachiocephalic vein + dilated SVC, all forming a widened superior mediastinum
- Lower circle (body of snowman) - enlarged heart (cardiomegaly)
- Increased pulmonary vascular markings - due to left-to-right shunting through ASD/PFO
Why This Silhouette Forms
| Structure | Contribution |
|---|---|
| Left vertical vein | Drains all 4 pulmonary veins upward |
| Left brachiocephalic (innominate) vein | Carries blood across the top |
| Dilated SVC | Receives all the anomalous flow |
| Together = | Wide upper mediastinum = "snowman head" |
This is supracardiac TAPVC, the most common type (~50% of TAPVC cases), where pulmonary veins drain to the SVC instead of the left atrium. - Harriet Lane Handbook, 23rd Ed.
TAPVC Classification
| Type | Drainage Site | % |
|---|---|---|
| Supracardiac | SVC via vertical vein | ~50% |
| Cardiac | Coronary sinus or right atrium | ~25% |
| Infracardiac | Portal vein/IVC (below diaphragm) | ~20% |
| Mixed | Multiple sites | ~5% |
Key Points
- Survival requires an ASD or PFO to allow oxygenated blood to reach the left side
- ECG: Right axis deviation + RVH
- Treatment: Surgical anastomosis of the pulmonary venous confluence to the left atrium
- Infracardiac TAPVC is the most dangerous (obstructed type - presents with severe cyanosis + pulmonary edema in neonates)
The snowman sign is pathognomonic for supracardiac TAPVC. - Rosen's Emergency Medicine; Goldman-Cecil Medicine
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