Children's Hospital Colorado
Colorado Fetal Care Center

Congenital High Airway Obstruction Syndrome (CHAOS)

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What is congenital high airway obstruction syndrome (CHAOS)?

Congenital high airway obstruction syndrome (CHAOS) is a complete or near-complete blockage of a baby’s upper airway. We can often diagnose this rare condition before birth. CHAOS causes overinflated lungs in unborn babies as well as an enlarged airway below the obstruction. The condition can also cause a flattened or inverted diaphragm.

While in the womb, babies usually release fluid from their lungs through their airway and out their mouth into the amniotic fluid, which surrounds babies during pregnancy. With CHAOS, the airway obstruction can trap fluid in the lungs. As a result, the lungs fill up and increase pressure in the chest. This pressure can decrease blood flow returning to the heart, which can result in non-immune fetal hydrops — fluid buildup in an unborn baby’s tissues and organs.

What causes congenital high airway obstruction syndrome?

Several conditions can lead to the diagnosis of congenital high airway obstruction syndrome, including:

  • Laryngeal atresia: blockage of the larynx, or voice box, due to underdevelopment
  • Subglottic stenosis: narrowing of the airway below the vocal cords
  • Agenesis of the laryngeal or tracheal rings: underdevelopment of the rings that provide structure for the larynx and trachea, which is the windpipe
  • Fraser syndrome: a congenital (present at birth) disorder characterized by ambiguous genitalia, urinary tract anomalies and laryngeal or tracheal anomalies

Who gets congenital high airway obstruction syndrome?

CHAOS is an extremely rare condition that occurs equally no matter a baby’s gender or race. Although it is considered a rare condition, some experts think the number of reported cases may be underrepresented because many cases have historically caused death in utero before a diagnosis. However, with new technology we can identify the condition earlier.

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