Steeple sign

Radiographic sign showing tapered subglottic tracheal narrowing resembling the pointed church steeple (spire). Caused by edematous subglottic arch and indicating inflammation in the upper airway. Possible causes are viral infections (parainfluenza, influenza, RS virus, adenovirus), bacterial infections (tracheitis, diphtheria), allergy (angioneurotic edema), and irritants (inhaling hot steam or smoke).