Fetal Surgery for Congenital High Airway Obstruction

Updated: Nov 05, 2019
  • Author: S Christopher Derderian, MD; Chief Editor: Hanmin Lee, MD  more...
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Congenital high airway obstruction syndrome (CHAOS) is defined by complete or near-complete obstruction of the upper airway and appears radiographically as echogenic large lungs, flattening or inversion of the diaphragm, and dilation of the tracheobronchial tree. [1, 2] It is a rare antenatal diagnosis whose true incidence is unknown, though it is likely more common than has been reported, in that many fetuses with the syndrome die in utero or are stillborn. [3, 4, 5, 6]

As the name suggests, CHAOS results from obstruction of the upper airway. Causes include laryngeal atresia, subglottic stenosis, and laryngeal or tracheal rings or agenesis. Laryngeal and tracheal anomalies may be associated with Fraser syndrome, a congenital disorder characterized by ambiguous genitalia, urinary tract anomalies, cryptophthalmos, and syndactyly. [7]  The literature is scant, but a 2016 study by Tessier et al suggested that approximately 40% of neonates diagnosed with Fraser syndrome had evidence of CHAOS before birth. [8]

The pathophysiology of CHAOS results from trapping of pulmonary secretions, which are normally evacuated through the fetal upper airway. Secretions accumulate in the bronchopulmonary tree and cause hyperinflation of the lungs. Excessive distention of the lungs, in turn, leads to an increase in the intrathoracic pressure, compromising venous return and cardiac output and potentially resulting in nonimmune fetal hydrops. It is noteworthy that hydrops is better tolerated by patients with CHAOS than by those with other congenital abnormalities associated with hydrops.

CHAOS is often diagnosed in the second trimester by means of ultrasonography (US), but it has been diagnosed as early as the first trimester. It is suggested by large echogenic lungs, flattening or bowing of the diaphragm, and fetal hydrops. [9]  Historically, fetal demise was unavoidable in the presence of CHAOS, but with the advent of the ex-utero intrapartum treatment (EXIT) procedure, survival rates have drastically improved. [10, 11, 12, 13]



The natural history of CHAOS is grim, with only one patient in 48 surviving the disease in the pre-EXIT era. [1] ​ Accordingly, the authors currently recommend that all viable fetuses with CHAOS undergo EXIT delivery. Rare instances of survival without an EXIT delivery have been described among patients with a concurrent tracheoesophageal fistula (TEF), providing a passage for evacuation of pulmonary secretions. [14]

In select patients who present with life-threatening hydrops and short-segment lesions or webs, fetoscopy with wire tracheoplasty may be of some benefit. [15]  Determining which patients are more likely to benefit from tracheoplasty poses a great challenge, and this procedure is typically reserved for fetuses who present with hydrops early in pregnancy (17-30 weeks’ gestation).

Because patients with CHAOS seem to tolerate hydrops better than those with other disease processes, expectant management is generally preferred for those who present later in the third trimester until an EXIT delivery can safely be performed. 

Given the complexity of in-utero management of CHAOS and the challenges of managing the difficult airway at birth, it is recommended that these cases be referred to a fetal care center. [16, 17]



Contraindications may be either maternal or fetal in origin. Maternal contraindications include the following:

  • Frequent contractions
  • Membrane rupture
  • Short cervix
  • Uncontrolled comorbidities that may predispose the patient to preeclampsia or HELLP (Hemolysis, Elevated Liver enzymes, Low Platelet count) syndrome

Fetal contraindications include the following:

  • Multiple fetal anomalies
  • Chromosomal abnormalities
  • Anatomic restrictions, including an anterior-lying placenta, which may prohibit safe access

Technical Considerations

Best practices

An EXIT-to-delivery procedure is the procedure most frequently performed in fetuses with CHAOS. The authors' current practice is to offer an EXIT delivery of all viable fetuses and to offer fetoscopy with wire tracheoplasty to hydropic patients with CHAOS who present between 17 and 30 weeks' gestation. Outcome data are limited.  

Fetal wire tracheoplasty is considered early in pregnancy. It is a challenging procedure that requires considerable preoperative planning. The procedure is performed fetoscopically under US guidance to avoid injury to the placenta. The fetal lie is a critical consideration because a direct path is required to introduce the fetal bronchoscope and guide wire; the procedure can be challenging, if not prohibitive, if the fetal head orientation is unfavorable. (See the image below.)

Fetoscopic approach for in utero tracheoplasty Fetoscopic approach for in utero tracheoplasty

In-utero laser treatment has also been described. In select cases, fetal US has been used to diagnose laryngeal atresia or tracheal web as the underlying cause of CHAOS. In one case, fetoscopic membrane perforation was performed successfully, resulting in lung size normalization and resolution of hydrops. [18]

Procedural planning

The EXIT procedure requires careful planning with a multidisciplinary team, typically including two pediatric/fetal surgeons, one obstetrician, one neonatologist, one ultrasonographer, and one nurse scrub.

Complication prevention

Appropriate anesthesia and tocolytics are important to prevent uterine contractions and placental separation. Uterine atony can lead to diffuse bleeding, and a special uterine stapler (uterine stapler with absorbable staples [US Surgical Corporation, Norwalk, CT]) can reduce the risk of hemorrhage during the EXIT procedure.



Because CHAOS is a very rare disease and viability beyond the immediate neonatal period became a reality only with the implementation of the EXIT procedure in 1998 and 2000, outcome data are limited. [10, 11, 12]  Case series support the assertion that long-term and tracheostomy-free survival are possible. [15]

Outcomes may depend on other anomalies, given that fetuses with CHAOS frequently have additional congenital abnormalities diagnosed postnatally. In one series, three of four fetuses with hydrops who underwent fetal intervention had other congenital abnormalities, consisting of prune-belly syndrome, imperforate anus, and fragile X syndrome. [15] In cases of isolated CHAOS without hydrops, outcomes are more favorable and frequently require shorter periods of postnatal ventilator support. [19]

Despite remarkable progress in CHAOS management, tracheostomy dependence and speech impediments are to be expected.

A diagnosis of CHAOS in the midsecond trimester suggests a poor prognosis, in that many progress to in-utero fetal demise (IUFD). Patients who present in the third trimester without signs of hydrops frequently survive until delivery, as they typically have only a partial obstruction.