What is the X-ray appearance of Transposition of the Great Arteries (TGA)?

X-ray Appearance of Transposition of the Great Arteries (TGA)

The chest X-ray in TGA typically shows a narrow mediastinal shadow due to the parallel relationship of the great arteries, with ventricular size and pulmonary markings varying based on patient status. 1

Radiographic Features of TGA

Key X-ray Findings

• Narrow mediastinum: The most characteristic finding is a narrow mediastinal shadow caused by the parallel orientation of the great arteries (aorta and pulmonary artery) 1
• Boot-shaped cardiac silhouette: In unrepaired TGA, particularly with pulmonary stenosis, there may be an "empty pulmonary artery bay" appearance 1
• Normal pulmonary vascularity: In patients with preserved ventricular function, pulmonary markings are typically normal 1

Post-Repair X-ray Findings

For patients who have undergone atrial baffle procedures (Mustard or Senning):

• Cardiomegaly may develop over time due to right ventricular enlargement
• Retrosternal fullness may be visible on lateral views if right ventricular dilation is present
• Surgical hardware or sternal wires from previous sternotomy 1

Clinical Context and Diagnostic Approach

Types of TGA

1. D-TGA (Dextro-TGA):

   • Most common form (accounts for 5% of all congenital heart disease) 1
   • Aorta arises from morphological right ventricle
   • Pulmonary artery arises from morphological left ventricle
   • Aorta is usually anterior to pulmonary artery 1

2. L-TGA (Levo-TGA or Congenitally Corrected TGA):

   • Less common variant
   • Characterized by both atrioventricular and ventriculoarterial discordance
   • May present with a different radiographic appearance 1

Limitations of X-ray in TGA

• X-ray alone is insufficient for comprehensive evaluation
• Cannot reliably assess:
  • Baffle leaks or obstructions (in post-repair patients)
  • Ventricular function
  • Associated defects (VSDs, outflow tract obstructions)

Advanced Imaging Recommendations

While chest X-ray provides initial information, more advanced imaging is required for complete assessment:

• Echocardiography: First-line for anatomic and hemodynamic assessment 1
• Cardiac MRI: Provides excellent assessment of ventricular size/function, baffle patency, and great vessel relationships 1
• CT: Alternative when MRI is contraindicated or unavailable 1

Clinical Implications

The X-ray findings in TGA have important implications for morbidity and mortality:

• Increasing cardiomegaly may indicate progressive right ventricular failure in patients with atrial switch repairs
• Development of pulmonary congestion may suggest baffle obstruction or ventricular dysfunction
• Monitoring for changes in cardiac silhouette is important for long-term follow-up

Common Pitfalls

• Mistaking the loud A2 (from anterior aorta) for P2 of pulmonary hypertension on clinical exam 1
• Overlooking subtle signs of right ventricular failure on chest X-ray
• Relying solely on X-ray findings without advanced imaging
• Failure to recognize that normal pulmonary vascularity does not exclude significant hemodynamic abnormalities

Adult patients with TGA require regular follow-up with specialists in adult congenital heart disease, with chest X-ray being just one component of a comprehensive imaging approach 1.