Congenital High Airway Obstruction Syndrome / CHAOS is detected by ultrasound as a complete or nearly complete obstruction of the upper airway.
The lungs appear extremely large. The diaphragm may be inverted and the heart compressed.
The heart may appear elongated with its chambers compressed by the enlarged large lungs.
The tracheobronchial tubes may be dilated and the fetus may have abnormal breathing movements.
Although a fetus diagnosed with Congenital High Airway Obstruction Syndrome (associated with hydrops) is unlikely to survive without fetal intervention, in some cases the hydrops resolves and the fetus can survive.