Congenital High Airways Obstruction Syndrome (CHAOS) and Bronchial Atresia

Definition

CHAOS is an extremely rare condition consisting of complete intrinsic obstruction of the fetal upper airway that can be located at the level of the larynx, trachea, or bronchi. Airway obstruction results in retention of bronchial secretions, which leads to abnormal expansion of the fetal lungs, marked tracheobronchial dilatation, and pulmonary developmental impairment.

Prevalence and Epidemiology

The incidence of CHAOS is unknown. Only a few cases have been reported in the literature.

Etiology, Pathophysiology, and Embryology

CHAOS may present as an isolated anomaly with a low risk of chromosomal anomalies, or in the context of a syndrome. When the obstruction is laryngeal, a significantly high proportion of cases are associated with Fraser syndrome, an autosomal recessive disease characterized by laryngeal atresia secondary to underlying fusion of the false vocal cords, cleft lip/palate, microphthalmia, syndactyly, ear anomalies, ambiguous genitalia, congenital heart disease, and severe oligohydramnios secondary to bilateral renal agenesis ( Chapter 129 ). In addition, other conditions can induce an extrinsic obstruction of the tracheobronchial tree, such as lymphatic congenital malformations, cervical teratoma, or vascular rings, such as double aortic arch or aberrant right subclavian artery.

The pathogenetic mechanism implicated for CHAOS includes intrinsic changes that prevented the normal development of the tracheobronchial tree during embryogenesis. The histopathologic findings of the fetal airways include the presence of webs, cysts, atresia, stenosis, or agenesis. Thus the cause of CHAOS can be a thin membrane, or web, obstructing the airway, or a more complex dysplasia and atresia of the affected portion of the airway. The obstructed flow of fetal lung fluid leads to intrapulmonary changes including alveolar hyperplasia and accumulation of fluid in the alveoli.