Congenital High Airway Obstruction (CHAOS)

Congenital high airway obstruction (CHAOS) is a rare but serious condition where a fetus’s airway is completely or almost completely blocked. When this happens, it can cause in utero complications such as:

• Swelling in the lungs
• Swelling in the trachea and bronchial tubes
• Heart failure
• Accumulation of fluid in different parts of the fetus’s body (hydrops)
• Mirror syndrome presenting with elevated blood pressure and abnormal blood work
• Intrauterine fetal death

Because of these risks, it’s important to diagnose and treat CHAOS quickly.

Signs of CHAOS include swollen and elongated lower trachea and bronchial tubes, which are usually discovered on a prenatal ultrasound. In more advanced cases, doctors may see the following:

• Fluid buildup in different parts of the fetus, such as in the abdominal cavity or under the skin, because the heart isn’t pumping blood properly (hydrops)
• Excess amniotic fluid around the fetus

CHAOS can be caused by several factors, such as:

• Laryngeal atresia: The fetus’s voice box (larynx) didn’t form a hole, so air can’t pass through.
• Laryngeal stenosis: The hole in the fetus’s voice box is too small, making it hard for air to get through.
• Laryngeal web: A thin wall of tissue blocks the fetus’s voice box like a spider web.
• Tracheal atresia: The windpipe (trachea), which carries air to the lungs, didn’t form at all.
• Tracheal stenosis: The windpipe is narrow, making it hard for air to pass through.
• Glottic atresia: Where the voice box opens and closes (vocal cords) is completely blocked.
• Tumors: A large lump or bump grows near the airway, pressing on it and causing a blockage.

Doctors and researchers are still working to understand what causes these issues.

Doctors typically detect CHAOS during a prenatal ultrasound. At Boston Children’s, our advanced prenatal imaging, including ultrasounds and MRI, provides clearer views of the fetus to identify the cause of the blockage and rule out other conditions, such as cystic adenomatoid malformation (CCAM). Our evaluation may include a fetal echocardiogram to assess heart function and structure, as well as genetic counseling to discuss family history and potential testing options to guide care and treatment.

Treatment for CHAOS mostly happens after birth and requires reconstruction of the upper airway. In cases of severe airway obstruction, we may consider in utero intervention to explore the obstruction and potentially open it, or ex utero intrapartum treatment (EXIT) to secure the airway before breathing begins outside of the uterus. With the EXIT procedure, our fetal surgeons deliver the fetus’s head and neck by opening the pregnant person’s abdomen and uterus, similar to a cesarean section, while the placenta continues to support the pregnancy through the umbilical cord, allowing an ENT specialist to evaluate the airway and insert a breathing tube to create an airway that enables breathing after delivery.

Surgeons may use several techniques during EXIT, such as:

• Laryngoscopy: To examine the larynx and bypass the obstruction with an endotracheal tube.
• Bronchoscopy: To inspect the bronchi and remove any cysts or membranes blocking the airway.
• Tracheostomy: If needed, a surgical opening is made in the trachea to provide a temporary airway.

In some cases, ECMO (heart-lung bypass) may be needed to support heart and lung function during the EXIT procedure.

Once the baby is stable and able to breathe, they are fully delivered, and the umbilical cord is cut. In some cases, surgeons can repair the obstruction during the EXIT procedure.

The long-term outlook for infants with CHAOS depends on the severity of the condition. If the obstruction is caused by a cyst or web in the larynx, the child is likely to develop normally with no lasting speech or health issues. In more severe cases, speech may be affected and tracheostomy may be needed.

Without treatment, CHAOS can lead to serious outcomes. About one-third of fetuses diagnosed with CHAOS may not survive, while others may face significant breathing complications. For third-trimester diagnoses without other major complications, the condition is often manageable with the EXIT procedure.

At Boston Children’s Fetal Care and Surgery Center, we work closely with your existing prenatal care providers to ensure seamless, expert care for treating CHAOS. Our coordinated, multidisciplinary team — including maternal-fetal medicine specialists, fetal and pediatric surgeons, ENT, neonatologists, fetal cardiologists, and other experts — collaborates closely to develop the most comprehensive treatment plan possible. From diagnosis through delivery, postnatal care, and beyond.