IS case 463: Acute laryngotracheobronchitis
Imaging Sciences URMC 2010
Publication Date: 2010-08-30
History
Patient is a 17-month-old male with asthma and frequent upper respiratory infections presenting with fever, cough and stridor. He was brought to the emergency department because of worsening increased work of breathing.
Findings
Frontal radiograph of the neck soft tissues demonstrated loss of the normal convex contour of the subglottic trachea. Lateral view demonstrated a normal epiglottis and aryepiglottic folds, with narrowing of the subglottic airway. The chest is clear with normal lung volumes.
Diagnosis
Imaging Sciences URMC 2010
Discussion
Laryngotracheobronchitis, or croup, is a clinical entity defined by inflammation of the subglottic airway secondary to viral infection which causes a characteristic stridorous cough. There is widespread involvement of the airway, but the cricoid cartilage surrounding the subglottic trachea confines the inflamed edematous tissue, causing preferential narrowing of the airway. There are more severe implications in younger children as airflow is impaired exponentially with decreasing size of the trachea. Also, their mucosa has a looser attachment to the submucosa, allowing greater propensity for the mucosa to expand due to edema. Organisms most commonly implicated include parainfluenza and respiratory syncytial virus, although occasionally a superimposed bacterial infection develops.
Croup is a common disease, accounting for up to 15% of primary care visits for respiratory infections in children and peaking in the second year of life. Patients present with symptoms of airway obstruction and respiratory distress after a viral prodrome of several days. The diagnosis is often clinical and requires no further testing. However, in the proper clinical scenario, for instance when onset is acute, croup can be confused with epiglottitis which is a life-threatening emergency, and radiographs are often used to exclude this diagnosis as well as foreign body and retropharyngeal abscess. Even then, patients may require admission for observation or intensive care if symptoms of respiratory compromise ensue.
Plain radiographs may demonstrate characteristic subglottic tracheal narrowing, referred to as the "steeple sign," however this appearance may be seen in epiglottitis as well. Other findings include overdistension of the hypopharynx on inspiration and haziness of the subglottic region. The epiglottis and aryepiglottic folds appear normal. These findings are up to 93% sensitive and 92% specific for croup. In situations where the clinical and radiologic findings are equivocal, observation or direct laryngoscopy may be performed.
References
- Everard ML. Acute bronchiolitis and croup. Pediatr Clin North Am. 2009 Feb;56(1):119-33, x-xi. PMID: 19135584
- Worrall G. Croup. Can Fam Physician. 2008 Apr;54(4):573-4. PMID: 18411388
- Desai A. Croup. eMedicine, Updated: Mar 15, 2010. http://emedicine.medscape.com/article/407964-overview
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