Practice Essentials
Stridor is a clinical sign characterized by monophonic, audible breath sounds (noisy breathing) that usually originates from the extrathoracic airways. [1] The presence of stridor indicates a partial obstruction of the upper airways, glottis, or trachea. The pitch of the stridor is determined by the degree of airway obstruction and the velocity of the airflow; the loudness and tone of the sound also varies by the specific cause. Congenital stridor presents at birth or within the first few weeks (4-6) of life. [2]
See the video of breath sound assessment, below.
Pathophysiology
Stridor results from partial obstruction of an airway with turbulent flow characteristics. Such respiratory tract areas are the upper airway, glottis, and trachea. The obstruction can be fixed or variable. Variable extrathoracic obstructions are primarily associated with inspiratory stridor. This is because, during inspiration, extrathoracic intraluminal airway pressure is negative relative to atmospheric pressure, leading to collapse of supraglottic structures. During expiration, intrathoracic pressure is positive and tends to collapse the airway. Thus, stridor caused by intrathoracic obstructions tends to be more prominent upon expiration. Stridor heard during both phases of respiration is usually due to either a fixed airway obstruction or to 2 areas of obstruction (ie, intrathoracic and extrathoracic).
Etiology
Differential diagnosis of stridor can be divided into supralaryngeal, laryngeal, tracheal, and nonanatomic categories.
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Supralaryngeal causes of stridor: Supralaryngeal causes include choanal atresia, vallecular cysts, thyroglossal cysts, and tongue dermoid or teratoma.
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Laryngeal causes of stridor
Laryngomalacia is the most common cause of congenital stridor. [3] Patients typically have high-pitched inspiratory stridor that increases with crying and when supine. It rarely interferes with feeding. Symptoms are usually present at birth or within the first 4-6 weeks of life. Laryngomalacia usually resolves of its own accord within 18-24 months. [4]
Vocal cord paralysis may cause a patient to have a weak cry. Patients may also be worse with feeding. Ruling out underlying conditions that may result in vocal cord paralysis, in particular neurologic conditions such as Arnold-Chiari malformation, is important. [5] Bilateral paralysis is more commonly associated with neurologic problems and is a life-threatening emergency.
Subglottic stenosis can be congenital or acquired. Stridor of subglottic stenosis is typically biphasic. Acquired forms usually arise from endotracheal (ET) intubation.
Other laryngeal abnormalities leading to stridor include webs, cysts, hemangiomas, papillomata, and laryngotracheoesophageal clefts. [6] Chu et al reported two cases of congenital laryngeal cysts that caused stridor in infants. [7]
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Tracheal causes of stridor
Extrinsic compression of the trachea by vascular abnormalities is a common cause of stridor. Anomalies that may lead to stridor include double aortic arch, innominate artery compression, aberrant right subclavian vein, and pulmonary artery sling. [8]
Bronchogenic cysts can also cause extrinsic compression of the trachea.
Tracheomalacia may be observed in association with laryngomalacia or as an isolated lesion.
Tracheal stenosis can be a complication of long-term ET intubation or a congenital lesion.
Complete tracheal rings are a subset of tracheal stenosis with severe biphasic airway sounds. Lipton and Nagler reported the case of an infant with complete tracheal rings and a pulmonary artery sling who presented with stridor. [9]
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Nonanatomic causes of stridor
Cardio-vocal syndrome occurs when cardiac abnormalities lead to compression of the recurrent laryngeal nerve.
Foreign body may be present.
Gastroesophageal reflux (GER) has been associated with stridor, although no controlled studies have been performed to demonstrate that GER is actually responsible for the stridor.
Epidemiology
Age-related demographics
Congenital stridor is present either at birth or shortly afterward.
Prognosis
The prognosis for congenital stridor depends on the specific cause. In general, it is very good.
For conditions such as laryngomalacia, the condition is self-limited and resolves on its own.
For other conditions, such as subglottic stenosis, surgical correction is curative.
Morbidity/mortality
Congenital stridor is rarely life-threatening. Immediately life-threatening obstruction from congenital lesions such as severe micrognathia are apparent at birth, and are treated with emergent tracheotomy. Bilateral vocal cord paralysis and subglottic hemangioma may present as causes of congenital stridor that are life-threatening. Significant airway obstruction can lead to respiratory distress and failure to thrive, secondary to the increased work of breathing.
Complications
The primary complication from congenital stridor is airway compromise and respiratory failure.
Other complications include failure to thrive secondary to increased work of breathing.
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Breath sound assessment. Video courtesy of Therese Canares, MD, and Jonathan Valente, MD, Rhode Island Hospital, Brown University.
