What does a steeple sign on a chest x-ray indicate?

Steeple Sign on Chest X-ray: Indicative of Croup

A steeple sign on a chest X-ray is strongly indicative of croup (laryngotracheobronchitis), characterized by subglottic tracheal narrowing that creates a conical appearance resembling a church steeple. 1, 2

Radiographic Appearance and Pathophysiology

The steeple sign appears as:

• Symmetrical narrowing of the subglottic trachea
• Conical or tapered appearance of the tracheal air column
• Most visible on anteroposterior (AP) views of the neck/upper chest
• Result of subglottic mucosal edema and inflammation

Clinical Correlation

When you observe a steeple sign, it should prompt consideration of:

1. Croup (Primary diagnosis):

   • Typically viral in etiology (most commonly parainfluenza virus)
   • Usually affects children but can rarely occur in adults 1, 3
   • Associated clinical features include:
     • Barking or "seal-like" cough
     • Inspiratory stridor
     • Hoarseness
     • Respiratory distress
     • Often preceded by upper respiratory symptoms

2. Differential considerations:

   • Bacterial tracheitis
   • Epiglottitis (though this typically presents with different radiographic findings)
   • Foreign body aspiration
   • Angioedema affecting the upper airway

Clinical Implications

The presence of a steeple sign has important management implications:

• Confirms diagnosis: Helps differentiate croup from other causes of upper airway obstruction
• Severity assessment: The degree of narrowing may correlate with clinical severity
• Treatment guidance: Indicates need for:
  • Humidified oxygen
  • Nebulized racemic epinephrine
  • Systemic corticosteroids
  • Antiviral therapy if influenza-related 1

Important Caveats

• A normal radiograph does not exclude croup (diagnosis is primarily clinical)
• The steeple sign may be absent in mild cases
• In adults, this finding is rare but has been documented in influenza A infection 1, 3
• The steeple sign should be distinguished from other radiographic signs like:
  • Deep sulcus sign (indicative of pneumothorax) 4, 5
  • Thumb sign (suggestive of epiglottitis)

Summary

When you encounter a steeple sign on chest X-ray, you should recognize it as highly suggestive of croup, prompting appropriate respiratory support measures and specific therapeutic interventions based on severity of symptoms and underlying etiology.