Subglottic stenosis is a condition characterized by narrowing of the subglottic airway (region below the vocal cords). It can be congenital or acquired 1.
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Epidemiology
Subglottic stenosis is the third most common congenital airway abnormality. The incidence of subglottic stenosis has decreased in recent decades after it was realized that endotracheal intubation (especially prolonged) greatly increases the risk of development 2-4.
Clinical presentation
The clinical features of subglottic stenosis are variable depending on the degree of severity. Mild subglottic stenosis may only present on exertion of with infection (causing swelling of tissues exacerbating stenosis). Clinical features include:
- asymptomatic
- stridor (usually biphasic)
- dyspnea
- hoarse voice
- severe respiratory distress
- cyanosis 5
Pathology
Subglottic stenosis is caused by a narrowing of the subglottic airways, which can be congenital or acquired.
Congenital subglottic stenosis is caused by defects at birth, which cause thickening of soft tissues and/or cartilage of the airway 1.
Acquired subglottic stenosis has multiple causes, but the most common is traumatic secondary to endotracheal intubation (often prolonged or incorrectly sized) 6. Intubation causes pressure on the walls of the subglottic airway, causes congestion and edema, ultimately leading to ulceration and necrosis 6. This is replaced by fibrous tissue that narrows the airway.
Other acquired causes include
- infection
- gastroesophageal reflux disease
- granulomatosis with polyangiitis
- extrinsic compression
Radiographic features
The best method of diagnosis is with direct visualization on bronchoscopy, however, imaging may aid in diagnosis and surgical planning. Plain radiographs, CT, and MRI of the neck may demonstrate narrowing of the trachea 6.
Ultrasound
Point of care ultrasound may be a useful tool in the bedside diagnosis of subglottic stenosis in emergent situations which may preclude lying supine, transportation to advanced imaging modalities, or performing bronchoscopy.
Using a linear probe in a transverse orientation on the midline, anterior neck the subglottis may be found just inferior to the cricoid cartilage 15. Bordered superficially by the characteristic uniform hyperechoic echotexture of the thyroid gland the anterior tracheal wall will appear as a curved, hyperechoic interface with reverberation artifacts posteriorly akin to an aerated lung. The greatest transverse diameter between hyperechoic air-mucosal interfaces should then be obtained; normal measurements fall between 17-24 mm with values that are below 15 mm suspicious for the presence of stenosis 14. Measurement of this diameter may also subsequently, if intubation is required, inform choice of the optimal endotracheal tube size 16.
Treatment and prognosis
Treatment includes both medical and surgical therapy. Medical therapy includes the use of steroids to reduce inflammation and edema 7, and proton pump inhibitors if reflux is thought to contribute. Surgical therapy may include endoscopic or open repair, stenting, or long-term tracheostomy 8,9.
Differential diagnosis
- laryngomalacia
- laryngotracheobronchitis
- vocal fold paralysis
- epiglottitis
- laryngospasm
- tumors
- aspirated foreign body
- bacterial tracheitis