Prenatal diagnosis of laryngeal atresia in two cases of congenital high airway obstruction syndrome (CHAOS).

Complete occlusion of the upper airways is known to cause secondary morphological changes, including bilaterally enlarged hyperechogenic lungs, dilated trachea, and hydrops. Prenatal diagnosis of upper airway obstruction has been described in several cases. In these reports, the diagnosis was primarily attributed to indirect signs, and the authors were in doubt as to whether the location of the obstructed area (larynx, glottis or trachea) could be precisely visualized by ultrasound. In this paper two cases are reported presenting the features of congenital high airway obstruction syndrome (CHAOS) diagnosed at the 22nd week of gestation. In both cases, the upper neck was perfectly visualized in a coronal plane. At the onset of fetal breathing movements, the stenotic larynx remained in a closed position. By positioning a colour signal on the fluid-filled dilated trachea, we noticed absence of flow throughout the onset of breathing activity. We conclude that the atretic area must be situated at the level of the larynx. Because of the poor prognosis of laryngeal stenosis and the presence of associated anomalies, both pregnancies were terminated in the 23rd week. This report shows that the application of colour and spectral Doppler may be helpful in the differential diagnosis of fetuses with CHAOS.