What does the scimitar sign on a radiograph indicate and how is it managed?

Scimitar Syndrome: Diagnosis and Management

The scimitar sign on a radiograph indicates partial anomalous pulmonary venous connection (PAPVC), specifically Scimitar syndrome, where part or all of the right pulmonary veins abnormally connect to the inferior vena cava through a characteristic curved vein resembling an Arabic sword. 1

Diagnostic Features and Evaluation

Radiographic Findings

• The "scimitar sign" appears as a tubular structure paralleling the right heart border on chest radiograph, representing the anomalous draining vein 1
• Additional radiographic findings may include dextrocardia, signs of vascular congestion, and right lung hypoplasia 1, 2

Associated Anomalies

• Right lung hypoplasia and/or anomalous bronchial or arterial anatomy 1
• Dextroposition of the heart 2
• Pulmonary sequestration 2
• May be associated with other cardiac defects 3

Recommended Imaging

• CMR (Cardiac Magnetic Resonance) or CTA (Computed Tomography Angiography) is recommended as first-line advanced imaging for evaluation of PAPVC including Scimitar syndrome 1
• CMR has advantages of:
  • No ionizing radiation exposure
  • Ability to quantify the degree of shunting
  • Superior visualization of extracardiac vascular anatomy 1
• Transesophageal echocardiography (TEE) can be useful when transthoracic echocardiography is inadequate, though less preferred than CMR/CTA 4

Hemodynamic Assessment

• Cardiac catheterization can be useful in adults with PAPVC to further define hemodynamics, especially in higher-risk patients being considered for surgical correction 1
• Provides direct measurement of pressures, quantification of shunt magnitude, and assessment of pulmonary arterial resistance 1

Management Approach

Indications for Surgical Intervention

Surgical repair is recommended when:

1. Symptomatic patients:

   • Functional capacity is impaired 1
   • Evidence of right ventricular volume overload is present 1

2. Significant hemodynamic impact:

   • Net left-to-right shunt sufficiently large (Qp:Qs ≥1.5:1) 1
   • PA systolic pressure less than 50% systemic pressure 1
   • Pulmonary vascular resistance less than one-third systemic 1

3. Even in asymptomatic adults with:

   • RV volume overload
   • Significant left-to-right shunt (Qp:Qs ≥1.5:1)
   • Acceptable pulmonary pressures and resistance 1

Surgical Options

• Direct reimplantation of the scimitar vein into the left atrium 1
• Conduit placement to the left atrium 1
• Intracaval baffling 1

Risk Factors and Outcomes

• Surgery for Scimitar syndrome is technically challenging with greater risk of postoperative vein thrombosis than simpler anomalous pulmonary vein abnormalities 1
• Infantile onset is an independent risk factor for stenosis or obstruction after repair 3
• Mortality after surgical repair is significantly higher in infants (37.5%) compared to non-infants (0%) 3
• Single ventricle physiology is associated with poor prognosis 3

Clinical Presentation and Natural History

Two Main Forms

• Infantile form: Presents within first 2 months of life with tachypnea, recurrent pneumonia, failure to thrive, and heart failure 2
• Childhood/adult form: Often asymptomatic or with milder symptoms 2

Follow-up Recommendations

• Asymptomatic patients without significant hemodynamic impact can be followed conservatively 2
• Regular monitoring for development of:
  • Right ventricular enlargement
  • Increasing shunt fraction
  • Pulmonary hypertension 1

Important Considerations

• Pulmonary hypertension is a significant risk factor for adverse outcomes with surgery 1
• Recurrent and/or progressive pulmonary vein obstruction can occur after surgical repair 1
• The severity of Scimitar syndrome depends on presenting age and associated congenital heart disease 3