What is congenital high airway obstruction syndrome (CHAOS), and why is it important to diagnose prenatally?
CHAOS is caused by an obstruction of the upper airway, either intrinsic (from atresia) or extrinsic (from a congenital mass). Imaging with ultrasonography (US) or fetal magnetic resonance imaging (MRI) demonstrates large lungs with an abnormal configuration of the diaphragm (convex down) and a dilated fluid-filled trachea to the level of obstruction. Ascites and/or hydrops fetalis may also be present. It is important to identify this disorder prenatally because a tracheostomy may be placed below the level of obstruction by a fetal surgical team during delivery (while placental circulation is maintained) if the diagnosis is known. It is also critical to diagnose the level of the obstruction, as an obstruction that is too low in the trachea may preclude placement of a tracheostomy.