Congenital high airway obstruction syndrome

Last revised by Dr Francis Deng on 11 Jan 2020

Congenital high airway obstruction syndrome or sequence (CHAOS) refers to a rare, often lethal, congenital laryngotracheal condition and is primarily characterized by obstruction to the fetal upper airway.

CHAOS can be of three possible types 2:

Ultrasound may show some or all of the following features 4,5

  • dilated trachea/bronchi: distal to the obstruction
  • enlarged and echogenic lungs
  • diaphragmatic inversion and/or flattening
  • presence of fetal ascites
  • the fetal heart may appear displaced to the midline and compressed

Ancillary sonographic features include

May confirm features detected on ultrasound as well as more accurately show the level of obstruction. Lung signal is increased 5

The prenatal natural history and postnatal course of CHAOS often depends on whether the airway obstruction is complete. An ex utero intrapartum treatment (EXIT) procedure may offer potential for salvage 1,3. Overall prognosis is considered generally poor 6.

The differential diagnosis of echogenic fetal lung is congenital cystic adenomatoid malformation (CCAM) type III. In CHAOS, both lungs are echogenic, whereas CCAM is usually unilateral, but can be bilateral in rare cases. Dilated airway is another clue which is seen only in CHAOS 9-11.

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Cases and figures

  • Case 1
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  • Case 2
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