Findings: Symmetrical subglottic narrowing on the AP view.

Diagnosis: Croup (Laryngotracheobronchitis).

Discussion: Croup is a syndrome that is produced by an acute infection of the lower air passages and is usually seen in children below age of 3, however there are always exceptions. Parainfluenza is the most common pathogen, however there are a variety of other respiratory viruses and even mycoplasma pneumonia which can cause croup.

Pathophysiology of croup is mucosal inflammation in the subglottic larynx and trachea that is circumferential in nature, with associated involvement and spasm of the vocal cords. Epiglottis is not involved.

Most consistent clinical finding is a barking or a brassy cough with or without stridor and hoarseness. Differential includes retropharyngeal abscess, foreign body, papilloma, epiglottis and fungal infections.

Croup is characteristically seen on an AP radiograph of the neck as a "pencil-shaped" configuration of the subglottic edema. This is sometimes referred to as the "steeple sign".

References:

1. Freundlich IM. Diseases Specific to Childhood. A Radiologic Approach
   to Disease of the Chest. 2nd Edition, pg 302.

2. Lebovics R, et al. Infectious Diseases of the Upper Respiratory Tract.
   Harrison's Principles of Internal Medicine. 13th edition, pg 519-520.