Aetiology
The aetiology of laryngomalacia (LM) is still not fully understood, although several theories have been proposed.
An anatomical theory suggests that LM occurs due to abnormalities in supraglottic anatomy.[11] Another theory proposes an underlying immaturity and flaccidity in the laryngeal cartilage that improves with age, although there have been no histological differences found in the cartilage of infants with LM compared with those without LM.
An alternative neurological theory is that neuromuscular incoordination or hypotonia arises from immaturity of the neural pathways (peripheral nerves and brainstem nuclei) contributing to supralaryngeal tone and laryngeal function.[12][13][14] Neurological abnormalities are found in up to 20% of children with LM.[14]
GORD has also been implicated and occurs in up to 80% of cases of LM.[14] Further work is required before the aetiology is fully understood.
Pathophysiology
LM occurs due to a predisposition to dynamic supraglottic collapse that occurs during the inspiratory phase of respiration. The underlying factors have not yet been fully determined and there are several possible mechanisms, which may co-exist in some patients.
Anatomical abnormalities, including short aryepiglottic folds and a curled 'omega-shaped' epiglottis, may contribute to the dynamic supraglottic narrowing.
Neural pathways may be immature with resulting neuromuscular incoordination or hypotonia of the supralaryngeal airway.
It has been proposed that the mucosal inflammation and oedema that results from GORD may narrow the supraglottic airway, with the increased obstruction thus contributing to the LM.[15]
Classification
Clinical classification of disease severity
Disease severity does not correlate with the intensity or frequency of stridor, but with the presence of associated symptoms. Several formal classification systems have been proposed, although none is in widespread use.[4][5][6] However, LM may be clinically classified as:
Mild disease: with audible stridor and endoscopic features of LM, but no respiratory distress and no evidence of failure to thrive (i.e., a steady growth on weight centile charts).
Moderate disease: with stridor, increased work of breathing, progressive feeding difficulties, and either weight loss or inadequate gain.
Severe disease: with significant shortness of breath and airway obstruction, failure to thrive, dysphagia, apnoeas, hypoxia or hypercapnia, pulmonary hypertension, cor pulmonale, obstructive sleep apnoea, severe chest deformity (pectus excavatum), and delayed neuropsychomotor development.
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