What is the 'figure 3 sign' on a chest X-ray (Chest X-ray) indicative of?

The "Figure 3 Sign" on Chest X-ray Indicates Coarctation of the Aorta

The "figure 3 sign" on a chest X-ray is indicative of coarctation of the aorta (option A). This radiographic finding is a characteristic sign that appears as an indentation or kinking at the site of aortic narrowing, creating a contour that resembles the number "3" 1.

Radiographic Features of Coarctation of the Aorta

Coarctation of the aorta (CoA) is a congenital narrowing of the aorta, typically occurring just distal to the left subclavian artery at the insertion of the ductus arteriosus. On chest X-ray, several findings may be present:

• Figure 3 sign: An indentation at the coarctation site produces a "3 sign" adjacent to the area beneath the transverse arch and above the main pulmonary artery silhouette 1
• Rib notching (typically ribs 3-8) due to collateral vessels 1
• Widening of the left subclavian artery 1
• Ectatic ascending aorta 1
• Double contouring in the descending aorta 1

Clinical Significance

Coarctation of the aorta has important clinical implications:

• It accounts for 5-8% of all congenital heart defects 1
• Prevalence is approximately 3 per 10,000 live births for isolated forms 1
• Often associated with other cardiac abnormalities, particularly bicuspid aortic valve (30-40% of cases) 1

Clinical Presentation

Patients with coarctation may present with:

• Upper body hypertension and lower body hypotension 1
• Blood pressure gradient between upper and lower extremities (>20 mmHg indicates significant CoA) 1
• Radio-femoral pulse delay 1
• Palpable collaterals 1
• Suprasternal thrill or vascular murmur in the back 1

Diagnostic Approach

While chest X-ray can suggest the diagnosis through the figure 3 sign and other findings, definitive diagnosis requires:

1. Echocardiography: Usually the initial imaging modality for suspected CoA 1

   • Provides information on site, structure, and extent of CoA
   • Assesses left ventricular function and associated cardiac abnormalities

2. Advanced Imaging: For comprehensive evaluation

   • CMR (Cardiac Magnetic Resonance) or CT: Preferred non-invasive techniques to evaluate the entire aorta 1
   • These modalities depict site, extent, and degree of narrowing, the aortic arch, and collaterals

3. Cardiac catheterization: Considered the gold standard in many centers 1

   • A peak-to-peak gradient >20 mmHg indicates hemodynamically significant CoA

Management Considerations

Intervention is indicated in patients with:

• Non-invasive pressure difference >20 mmHg between upper and lower limbs 1
• Upper limb hypertension (>140/90 mmHg) 1
• Pathological blood pressure response during exercise 1
• Significant left ventricular hypertrophy 1

Even with a smaller pressure gradient, hypertensive patients with ≥50% aortic narrowing relative to the aortic diameter at the diaphragm level should be considered for intervention 1.

Differential Diagnosis of the Other Options

• Pulmonary embolism (B): Does not typically produce a figure 3 sign on chest X-ray
• Mitral stenosis (C): May show pulmonary congestion and left atrial enlargement, but not a figure 3 sign
• Aortic stenosis (D): May show post-stenotic dilation of the ascending aorta and left ventricular enlargement, but not a figure 3 sign

The figure 3 sign is a specific radiographic finding that strongly points to coarctation of the aorta, making option A the correct answer.