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Croup (acute laryngotracheobronchitis) on X-ray with steeple sign

Croup, also called acute laryngotracheobronchitis is caused by viral infection of the upper airway usually parainfluenza virus or respiratory syncytial virus (RSV). It is common and has a peak incidence before the age of 1 year (typically between 3 and 6 months of age).

It is presented Clinically by protracted barking cough and inspiratory stridor due to tracheal narrowing that is caused by mucosal oedema .

X-ray finding :
On Plain film
The diagnosis of acute laryngotracheobronchitis or Croup is usually made clinically
and no need for doing may do it just for excluding other causes of same presentation like:
- foreign body aspiration.........tracheal or oesophageal.
- angioneurotic edema
- epiglottitis and epiglottic-cysts
- congenital subglottic stenosis

However there are some typical radiographic findings :

1- steeple sign (the image above): seen on AP radiographs of the neck or chest and neck demonstrates uniform narrowing of the subglottic airway

But What is steeple sign ??
The steeple sign refers to superior tapering of the trachea on a frontal chest radiograph. It is remaniscient of a church steeple and is suggestive of croup.

2- distension of the hypopharynx is also seen due to the patient's attempt at decreasing airway resistance (the image below)