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Congenital High Airway Obstruction Syndrome (CHAOS)

Congenital high airway obstruction syndrome is a rare congenital anomaly caused by laryngeal or tracheal atresia, tracheal stenosis or web, or, rarely, compression from a double aortic arch . There is outflow obstruction of the fetal lung fluid, which leads to pulmonary hyperplasia. Prenatal US findings (Fig 13a, 13b) include symmetrically enlarged echogenic lungs, dilated and fluid-filled trachea and bronchi, and inverted hemidiaphragms. The heart appears small compared with the enlarged lungs and appears somewhat anteriorly positioned in the chest due to compression by the lungs. Hydrops may be present. Fetal MR imaging in congenital high airway obstruction syndrome demonstrates enlarged, hyperintense lungs with flattened or inverted hemidiaphragms. Visualization of a dilated airway helps localize the level of obstruction.

Figure 13a

Congenital high airway obstruction syndrome. (a, b) Transverse (a) and coronal (b) US images through the fetal chest show enlarged hyperechoic lungs compressing the heart. Note the inversion of the diaphragm (arrow in b) and the dilated trachea and bronchi (arrowheads in b). These findings suggest the presence of congenital high airway obstruction syndrome, likely from tracheal atresia.

Figure 13b

Congenital high airway obstruction syndrome. (a, b) Transverse (a) and coronal (b) US images through the fetal chest show enlarged hyperechoic lungs compressing the heart. Note the inversion of the diaphragm (arrow in b) and the dilated trachea and bronchi (arrowheads in b). These findings suggest the presence of congenital high airway obstruction syndrome, likely from tracheal atresia.

At pathologic examination, the lungs are massively enlarged and edematous (Fig 13c, 13d).

Figure 13c

Congenital high airway obstruction syndrome.  (c) Photograph of the gross autopsy specimen demonstrates enlarged and edematous lungs secondary to tracheal atresia.

Figure 13d

Congenital high airway obstruction syndrome. (d) Photomicrograph (original magnification, ×4; H-E stain) shows an increase in the number and size of airspaces, which are poorly subdivided (compare with the normal fetal lung in Fig E2 [online]).

If a confident diagnosis is made prenatally, an ex utero intrapartum treatment (EXIT) procedure at the time of planned cesarean section may help establish a functional airway, which is the only hope for survival in this otherwise fatal condition. 

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