Chronic Stridor

The most common cause for inspiratory stridor is laryngomalacia, which accounts for approximately 75% of all cases of neonatal stridor. Laryngomalacia results from the immature cartilage of the upper larynx collapsing inward during inhalation, causing airway obstruction. Vocal cord dysfunction, the second leading cause of stridor in the neonatal period, can be congenital or iatrogenic, such as from damage to the left recurrent laryngeal nerve during ligation of a patent ductus arteriosus or from direct injury to the vocal cord during endotracheal intubation. Congenital subglottic stenosis occurs when there is incomplete canalization of the subglottic airway and cricoid rings. Subglottic stenosis is most often acquired after prolonged intubation in the neonatal period, usually in the setting of extreme prematurity. Tracheomalacia results from a defect in the tracheal cartilage that causes a “floppy” airway lacking the rigidity necessary to maintain patency. Tracheomalacia is the leading cause of expiratory stridor. Tracheal stenosis can be caused by the presence of complete tracheal rings instead of the normally C-shaped rings. Stridor can also result from tracheal compression caused by vascular rings such as a double aortic arch. Other less common causes of chronic stridor include laryngeal papillomas caused by maternal human papillomavirus infection, webs, cysts, hemangiomas, and laryngeal dyskinesia.

Acute Stridor

The causes of acute stridor are primarily infectious in cause with two notable exceptions, foreign body aspiration and allergic reaction. The most common cause of acute stridor is laryngotracheobronchitis, or croup (Figure 36-2). Croup is classically caused by parainfluenza virus but can also be caused by respiratory syncytial virus, influenza, adenovirus, and Mycoplasma pneumoniae. Bacterial tracheitis, usually caused by Staphylococcus aureus, is an uncommon but life-threatening condition that occurs most frequently as a bacterial superinfection in patients who have viral croup.

Figure 36-2 Croup.

Retropharyngeal and peritonsillar abscesses are common infections that can present with acute stridor. Both infections are usually polymicrobial, including β-hemolytic streptococci; oral anaerobic bacteria; and in retropharyngeal abscess, S. aureus. Finally, epiglottitis, traditionally caused by Haemophilus influenzae type B (Hib), is now a rare cause of stridor as a result of the widespread use of the conjugated Hib vaccine.

Chronic Stridor

Laryngomalacia can present at birth but usually presents at 2 to 4 weeks of age. The inspiratory stridor of laryngomalacia is exacerbated when the infant lies supine, cries, or when feeding and is alleviated when the infant is prone.

Vocal cord paralysis can be unilateral or bilateral. Bilateral vocal cord paralysis results in aphonia and high-pitched biphasic stridor, with significant respiratory distress. Unilateral paralysis can cause inspiratory or biphasic stridor, as well as a weak or hoarse cry.

Whereas subglottic stenosis and vascular rings may likewise present with inspiratory or biphasic stridor, tracheomalacia usually presents with expiratory stridor. Tracheomalacia may present with a monophonic wheeze if the obstruction is intrathoracic.

Acute Stridor