Congenital High Airway Obstruction Syndrome (CHAOS)

What is CHAOS?

CHAOS stands for Congenital High Airway Obstruction Syndrome. It is a very rare congenital condition of the  fetus that can block their airway at birth, with the following characteristics:

  • Very enlarged lungs
  • Flat diaphragm
  • Dilated tracheobronchial tree
  • Ascites (fluid in the abdomen)
  • Other signs of hydrops (heart failure in the fetus) because of the obstructed airway

The diagnosis can be done antenatally. A complete or partial obstruction of the upper airway can be visualized with ultrasound. Some of the ultrasound features are:

  • Both lungs may seem symmetrically enlarged and echogenic.
  • The diaphragm can be inverted or flat.
  • The heart may be compressed and appear elongated from compression of large lungs.
  • The tracheobronchial tubes may seem dilated and filled with fluid.
  • Abnormal breathing movements can be visualized.
  • Signs of hydrops/heart failure (fluid in the skin, lungs, heart, abdomen)

What causes CHAOS?

The underlying cause of Congenital High Airway Obstruction Syndrome (CHAOS) is an obstructed airway, which may be due to:Blockage or total absence of the larynx (laryngeal stenosis or atresia)

  • Blockage or total absence of the trachea (tracheal stenosis or atresia)
  • Presence of a cyst or web blocking the airway
  • Compression from a double aortic arch (although rare)

What is the prognosis (outcomes) for a fetus with CHAOS?

The presence of a patent airway is important not only after birth but also during the pregnancy. The accumulation of fluid in the lungs due to blockage can cause the lungs to become enlarged and compress the neighboring heart. This may result in congestive heart failure in the fetus. This condition may be fatal; only a few cases of long-term survival have been described.

What other tests should we consider?

  • A detailed ultrasound to detect other associated anomalies in the fetus
  • A fetal echocardiogram to detect cardiac defects
  • Chromosome analysis (karyotype) to rule out chromosomal abnormalities
  • Serial ultrasounds for signs of heart failure
  • Fetal MRI may be considered (localization of the level of obstruction)
  • Consultations with Maternal Fetal Medicine, Genetics, Pediatric Surgery to plan for delivery in a tertiary care center and EXIT (ex utero intrapartum treatment) procedure

What therapy is available?

Fetal intervention can be offered for Congenital High Airway Obstruction Syndrome. However, this will depend on the gestational age at diagnosis and associated abnormalities (other structural anomalies, chromosomal abnormalities and signs of hydrops).

In very rare cases of early gestation, open fetal surgery may be discussed due to high risk of intrauterine death.

However, after 30 weeks gestation, an EXIT (ex utero intrapartum treatment) procedure may also be performed at the time of cesarean section to establish a functional airway. A multidisciplinary team will be present at delivery including:

  • Anesthesia and Respiratory Therapist
  • Neonatology
  • Otolaryngology (ENT)
  • Maternal Fetal Medicine
  • Nursing

After birth, some babies may require surgery to manage the blocked airway or ECMO (Extracorporeal Membrane Oxygenation).

Where can I get more information?

Cincinnati Children’s

UCSF Benioff Children’s Hospital

Special Pregnancy Program

Referrals »

Fetal Medicine: 416-586-4800 x 7756
Fax: 416-586-3216

Maternal Medicine: 416-586-4800 x 7000
Fax: 416-586-5109

Main clinic hours: Monday to Friday, 8am to 4pm

Prenatal Diagnosis & Medical Genetics

Referrals »

phone: 416-586-4800 x 4523
fax numbers:
416-586-4723 or 416-586-8384

Perinatal Mental Health

Referrals »

Phone: 416-586-4800 x 8325
Fax: 416-586-8596