Croup, or acute laryngotracheobronchitis, remains a common cause of upper airway obstruction. Croup is viral, most commonly parainfluenza, and is seen mostly in the fall and winter when parainfluenza is more common. Croup is seen in a younger population than epiglottitis (usually 6 months to 3 years). Croup presents with a distinctive barking cough and is self limited, lasting about a week.
A lateral soft tissue radiograph will show the AP narrowing of the subglottic trachea, which normally should maintain the same AP diameter to the thoracic inlet. An AP soft tissue neck film will also show subglottic narrowing, but this can be confused with normal respiration changes. CXR will usually show signs of the viral bronchitis. Most importantly, the radiographic examination will also determine if there is a retropharyngeal abscess or an airway foreign body.