Congenital high airway obstruction syndrome

Last revised by Ammar Ashraf on 19 Dec 2023

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 echogenic lungs

  • diaphragmatic inversion and/or flattening

  • 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 depend 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 pulmonary airway malformation (CPAM) type III. In CHAOS, both lungs are echogenic, whereas CPAM is usually unilateral, but can be bilateral in rare cases. Dilated airway is another clue that is seen only in CHAOS 9-11.

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