Introduction
Congenital high airway obstruction syndrome (CHAOS) is a rare condition caused by laryngeal or tracheal atresia, tracheal stenosis, laryngeal cysts, and tumors of the oropharynx and cervical region, or due to compression from a double aortic arch. It is a serious condition in which the fetal airway is blocked. It is a life-threatening condition if left untreated.
What Is Congenital High Airway Obstruction Syndrome?
Congenital high airway obstruction syndrome refers to the obstruction of the fetal airway. The obstruction can occur in any region of the airway. The fetal lungs secrete fluid before birth under positive pressure. The obstruction traps the fluid inside the lungs. This results in large, overinflated lungs that compress the heart and disrupt its function. This leads to fluid accumulation in various regions, including the fetus's abdomen, skin, and scalp.
Various conditions can cause the obstruction, that include:
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Laryngeal Atresia - This is the most common cause of obstruction. Partial development of the larynx (voice box) interrupts or blocks the airway.
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Tracheal Atresia - Partial development of the trachea (windpipe) interrupts or blocks the fetal airway.
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Tracheal Agenesis - Complete absence of the trachea.
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Tracheal Stenosis - Narrowing the trachea or larynx segment obstructs the airway.
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Fluid-Filled Cysts or Tumors - Obstruct the airway.
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A Web-Like Membrane - Obstructs the trachea or larynx.
What Are the Causes of Congenital High Airway Obstruction Syndrome?
The cause remains unknown. It is related to genetic syndromes like Fraser syndrome, short-rib polydactyl syndrome, Shprintzen-Goldberg omphalocele syndrome, and chromosomal abnormalities like 22q11.2 deletion, deletion of chromosome 5p, 47, XXX, partial trisomy 9, and partial trisomy 16q. Genetic testing through amniocentesis during pregnancy is important to diagnose such conditions.
What Are the Signs and Symptoms of CHAOS?
The signs are discovered during prenatal ultrasound.
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The fetal lungs are enlarged and echogenic on both sides. The bronchial tree appears dilated.
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The diaphragm (respiratory muscle) is displaced downward.
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The heart is compressed and shifted to the middle of the chest.
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Fluid accumulation is seen in the fetal abdomen as in ascites, in the skin, and scalp (hydrops).
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The amniotic fluid level increases (polyhydramnios) due to the compression of the esophagus (food pipe).
How Is CHAOS Diagnosed?
Prenatal tests used in the diagnosis of CHAOS are:
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Genetic testing during pregnancy through amniocentesis.
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A high-resolution ultrasound shows enlarged lungs that compress the heart and displaced anatomy.
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A fetal echocardiogram is done to evaluate the structure and function of the heart.
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A prenatal MRI (magnetic resonance imaging) scan evaluates the fetus's upper airway.
How Are the Complications Managed During Pregnancy?
Management of complications during pregnancy depends on the type and location of the obstruction in the fetal airway. Regular fetal ultrasounds are done to monitor for signs of fetal heart failure. Compression of the esophagus leads to an increase in amniotic fluid and increases the risk of preterm labor. Amnioreduction is done to prevent this risk. It involves the placement of a thin needle into the amniotic space to remove excess fluid. Antenatal monitoring is started in the third trimester to observe fetal well-being and decrease complications risk.
How Are Complications Managed in the Fetus?
The obstruction resolves on its own, sometimes in cases of tracheal web membrane or cyst. The mother is given antibiotics and sedation via the intravenous route. This also sedates the fetus. A trocar (hollow needle) is inserted into the uterus through a small incision in the mother's abdomen to reach the fetal airway. This is done under the guidance of ultrasound and color flow doppler. This fetoscopic procedure is done to visualize the obstruction and puncture or fenestrate the obstruction. This puncture allows the escape of the trapped fluid in the fetal lungs. This results in the normalization of the lung size, the dilated tracheobronchial tree, the position of the diaphragm, amniotic fluid volume, and the resolution of ascites or hydrops. This procedure, called fetal wire tracheoplasty, used to treat CHAOS, requires early diagnosis and evaluation.
How Is a Fetus With CHAOS Delivered?
The baby takes its first breath through the airway after birth. A fetus with airway obstruction cannot survive after birth as it does not receive oxygen. The fetus with airway obstruction is delivered via an EXIT (ex utero intrapartum treatment) procedure. This procedure can be done only if the airway obstruction was identified during prenatal ultrasound. The mother is anesthetized, and an incision is made in the abdomen. In this, the fetus is partially delivered through the opening in which the fetus is still attached to the mother's placenta.
The baby receives oxygen support and nutrients from the placenta, which provides time for the surgeon to establish an airway in the form of intubation into the mouth or tracheostomy (a tube is surgically inserted into the trachea in front of the neck) below the obstruction. Once the airway is established, the fetus is fully delivered. This allows the baby to receive oxygen and improves survival. The EXIT procedure is contraindicated if the mother has frequent contractions, membrane rupture, a short cervix, and comorbidities like preeclampsia. It is contraindicated if the fetus has multiple anomalies, chromosomal abnormalities, and anatomic restrictions like the anterior-lying placenta, which inhibits access. If the airway cannot be established on time, the baby is placed on an ECMO machine (extracorporeal membrane oxygenation).
How Is CHAOS Treated After Birth?
The baby is shifted to the NICU (newborn/infant intensive care unit). The baby is monitored for breathing assistance. Medications and nutrition are given through an intravenous catheter inserted into the vein or the umbilical cord. The baby is kept in the NICU until it breathes on its own, feeds by mouth or feeding tube, maintains the temperature, and gains weight. If the obstruction is minor, it can be treated with minimal surgery. If the obstruction is severe or a segment of the trachea is missing, it requires multiple surgical procedures to repair the airway.
Conclusion
Congenital high airway obstruction syndrome is a rare respiratory abnormality. Early prenatal diagnosis and management increase the survival rate. Advancements in genetic testing, prenatal imaging, intervention techniques, and postnatal care have improved long-term outcomes.
