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Congenital High Airway Obstruction Syndrome


Key Points

  • Congenital high airway obstruction syndrome (CHAOS) is characterized by bilaterally enlarged lungs, flat or inverted diaphragms, dilated tracheobronchial tree, and massive ascites due to complete airway obstruction.

  • CHAOS is often mistaken for bilateral congenital pulmonary airway malformations.

  • MRI is helpful in diagnosing CHAOS and excluding potential associated findings.

  • CHAOS can be associated with syndromes such as Fraser syndrome.

  • The natural history of CHAOS may be divided in thirds: 1/3 die in utero; in 1/3 the hydrops remains stable; and in 1/3 the hydrops resolves following spontaneous perforation.

  • Fetoscopic treatment of the tracheal or laryngeal obstruction is possible in select cases.

  • EXIT procedure is indicated to deliver all cases of CHAOS due to critical airway obstruction.


Congenital high airway obstruction syndrome (CHAOS) is a prenatally diagnosed clinical syndrome manifested by the presence of extremely large echogenic lungs, flattened or inverted diaphragms, a dilated tracheobronchial tree, ascites, and other manifestations of nonimmune hydrops due to complete obstruction of the fetal airway (Hedrick et al., 1994). No fetus diagnosed prenatally with CHAOS associated with hydrops and complete airway obstruction has survived without intervention. The exception to this occurs when there is spontaneous perforation of the laryngeal or tracheal atresia, which may occur in up to one-third of cases and results in resolution of the hydrops.


The airway obstruction in CHAOS may be due to one of several causes, including laryngeal atresia, tracheal atresia, or laryngeal cyst, but the fetal clinical presentation is the same. Three types of laryngeal atresia are recognized: type I, in which the supraglottic and infraglottic parts of the larynx are atretic; type II, in which the atresia is infraglottic; and type III, which is glottic. A wide range of anomalies can be seen in association with laryngeal atresia (Table 30-1). Some fetuses, however, have atresia as an isolated anomaly (Fox and Crocker, 1964).


Congenital obstruction of the fetal airway resulting in CHAOS was initially thought to be extremely rare (Hedrick et al., 1994). Only 55 cases of this syndrome have been reported since 1989 (Wigglesworth et al., 1987; Delechotte et al., 1988; Silver et al., 1988; Tournier et al., 1988; Arizawa et al., 1989; Fang et al., 1989; Scurry et al., 1989; Didier et al., 1990; Schauer et al., 1990; Watson et al., 1990; Richards et al., 1992; Weston et al., 1992; Hedrick et al., 1994). However, this syndrome may be more common than generally appreciated because many of the affected fetuses die in utero or are stillborn (Fox and Crocker, 1964; Smith and Bain, 1965; Cohen, 1971; Wigglesworth et al., 1987; Fang et al., 1989; Scurry et al., 1989; Schauer et ...

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