Congenital Subglottic Stenosis

Congenital subglottic stenosis is narrowing of the airway at the level of the cricoid cartilage, present from birth, without prior intubation or trauma. It is defined by a cricoid lumen under 4.0 mm in a term neonate and under 3.5 mm in a preterm infant.

It is the second most common congenital laryngeal anomaly after laryngomalacia, and the commonest cause of chronic airway obstruction in infancy that is not acquired. It may be associated with Down syndrome, other syndromes, and cardiac or other airway anomalies.

Severity is graded by the percentage of lumen obstruction: grade I up to 50%, grade II 51 to 70%, grade III 71 to 99%, and grade IV no detectable lumen.

Pathophysiology.

A membranous form results from thickened submucosal tissue with fibrosis and hyperplastic mucous glands. A cartilaginous form arises from an abnormally shaped, small, thick cricoid ring.

The airway is narrowest at the cricoid, so even slight oedema from infection or intubation causes large increases in airway resistance.

• Biphasic or inspiratory stridor, often noted at birth or in the first months, worse with agitation, feeding and respiratory infection.
• Recurrent or prolonged croup episodes, with a barking cough and a weak or normal cry.
• Failed extubation or inability to pass an endotracheal tube of the usual size for age.
• Severe: cyanotic episodes, retractions, feeding difficulty and failure to thrive.

Red flags.

• Stridor at rest, respiratory distress or cyanotic episodes.
• Failed extubation, recurrent severe croup, or poor weight gain.
• Down syndrome or other airway anomalies, haemangioma or cardiac disease.

• Flexible nasopharyngolaryngoscopy as an initial assessment of the supraglottis and vocal cords.
• Direct laryngoscopy and bronchoscopy under general anaesthetic with spontaneous ventilation to view the subglottis, and to rule out other anomalies. Measure the lumen using graduated endotracheal tubes to grade the stenosis.
• Neck X-ray (steeple sign), CT airway or MRI where needed, and echocardiography to look for vascular or cardiac anomalies.
• Reflux assessment, as laryngopharyngeal reflux worsens oedema.

Differential diagnosis. Acquired subglottic stenosis, laryngomalacia, subglottic haemangioma, laryngeal web or cleft, vocal cord paralysis, tracheomalacia, vascular ring and croup.

• Mild disease (grades I and II): observation as the airway grows, with treatment of croup episodes with dexamethasone 0.15 mg/kg orally and nebulised adrenaline 0.5 mL/kg of 1 in 1000 (maximum 5 mL). Treat reflux and avoid intubation where possible.
• Endoscopic options: balloon dilatation, laser or cold steel division of a soft membranous web, with or without topical mitomycin or steroid injection. Results are better for membranous stenosis.
• Open surgery for grade III or IV disease or failed endoscopic treatment: anterior cricoid split in neonates who need ventilation, laryngotracheal reconstruction with anterior or posterior costal cartilage graft, or cricotracheal resection in severe cases.
• Tracheostomy for severe obstruction as a temporising measure until reconstruction.
• Perioperative care: stenting, ventilation, antibiotics, steroids and antireflux treatment.

Monitoring. Symptoms, growth, airway endoscopy after surgery at intervals until decannulation, voice and swallowing.

Referral and escalation. Refer to a paediatric airway surgical service for any infant with persistent stridor or recurrent croup, or failed extubation. Use the smallest suitable tube for emergency intubation.