Croup, also called acute laryngotracheobronchitis is due to viral infection of the upper airway by parainfluenza virus or respiratory syncytial virus (RSV).
On imaging, although not required for the diagnosis, it classically presents with a narrowing of the subglottic airway and ballooning of the hypopharynx.
Croup can happen in children as young as 6 months age up to 15 years but most commonly between 6 months to 3 years with the peak at 18 months. It is the most common cause of upper respiratory distress in infants and young children which usually occurs in late fall to early winter 3.
Clinically it presents with protracted barking cough and inspiratory stridor due to mucosal oedema resulting in tracheal narrowing.
Plain radiographs are not always required, as the diagnosis is often made clinically. They are usually obtained to exclude other causes of a similar presentation. Typical radiographic findings include:
- steeple sign: seen on AP radiographs of the neck or chest and neck demonstrates uniform narrowing of the subglottic airway; also referred to as a wine bottle sign
- distension of the hypopharynx is also seen due to the patient's attempt at decreasing airway resistance
- lateral radiograph of the upper airway will show a normal epiglottis and narrowing of the subglottic region.
Treatment and prognosis
Croup is usually self-limiting and has a good overall long-term prognosis.
Treatment is directed toward improving air exchange. Conservative measures, nebulised adrenaline (epinephrine) and corticosteroids are commonly used.
General imaging differential considerations include:
- 1. Huisman TA. Pediatric Imaging. Mosby. (2010) ISBN:0323066984. Read it at Google Books - Find it at Amazon
- 2. Salour M. The steeple sign. Radiology. 2000;216 (2): 428-9. Radiology (full text) - Pubmed citation
- 3. Bjornson CL, Johnson DW. Croup in the paediatric emergency department. Paediatr Child Health.12 (6): 473-477. Free text at pubmed - Pubmed citation
- 4. Donnelly LF. Pediatric Imaging. Saunders. (2009) ISBN:1416059075. Read it at Google Books - Find it at Amazon