Disorders affecting a fetus’s head or neck are caused by a variety of factors, but often are associated with other genetic disorders. Their treatment and outcome depend on the stage of gestation when the diagnosis is made, severity of the disorder, and many other individual factors.
Congenital High Airway Obstruction Syndrome (CHAOS)
When a fetus’s trachea or larynx experiences a blockage, it is called Congenital High Airway Obstruction Syndrome, or CHAOS. It can be caused by several factors, which include missing a portion of the trachea (a condition known as atresia), narrowing of the airway, or the presence of a membrane. Whatever the cause, this blockage traps lung fluid that normally escapes from the fetus’s mouth and, as the lungs become distended with fluid, it can affect the heart’s function. It can even lead to hydrops, or congestive heart failure, which can be fatal and should be managed by a maternal-fetal medicine specialist.
CHAOS is diagnosed by ultrasound, and treatment depends upon the gestational age at diagnosis and whether hydrops is present. When suspected, a maternal-fetal specialist will perform a thorough examination and offer genetic testing to look for other congenital and chromosomal abnormalities. In very rare cases where the fetus is at significant risk of death, open fetal surgery may be performed. In cases where the fetus is more than 30 weeks old, an EXIT (ex utero intrapartum treatment) procedure may be performed to provide the baby with a functioning airway at the time of birth.
Cystic hygromas are one or more fetal neck cysts that form and continue to grow over time. They are caused by malformations in the lymphatic system, and about half of all fetuses with cystic hygroma have abnormalities in their chromosomes. About 60% of cystic hygromas are caused by genetic disorders and chromosomal abnormalities, although they also are caused by environmental factors such as viral infections passed from the mother to baby during pregnancy or exposure to drugs or alcohol. Cystic hygroma can occur either in early or late pregnancy and can be diagnosed by prenatal ultrasound.
In Early Pregnancy
In the first trimester, cystic hygromas are associated with an increased risk for fetal trisomy, especially trisomy 21. In the second trimester, a cystic hygroma may be the clinical presentation of Turner syndrome. Additionally, a cystic hygroma can be present in a healthy baby. If a chromosome abnormality is not found in the fetus, the outcome is generally better than for those who do have a chromosome abnormality.
Overall, there is generally a poor prognosis associated with the prenatal finding of cystic hygroma. Studies have indicated that smaller cystic hygromas are more likely to resolve. Oligohydramnios (not enough amniotic fluid) or polyhydramnios (too much amniotic fluid) predicts a poor outcome. Hydrops occurs 22-76% of the time with a cystic hygroma and is almost always associated with miscarriage or fetal death.
In Late Pregnancy
When cystic hygromas appear in late pregnancy, they usually are not associated with other abnormalities. However, babies with cystic hygroma should be delivered at a specialty care center that can provide the appropriate care and support. If the cystic hygroma is large, a Caesarean section may be required for delivery. There is a chance of recurrence after surgical removal of the cystic hygroma.
Although uncommon, a fetal goiter is typically associated with fetal hyperthyroidism and hypothyroidism. Most cases of congenital goiter are identified after birth when a neonate is detected to have hypothyroidism by newborn screening tests. In contrast, fetal goiters are diagnosed by ultrasound, which will show a mass that will vary in size. Depending on the size of the fetal neck mass, the baby’s head may be hyperextended, and it may cause polyhydramnios, which is an excessive buildup of the amniotic fluid surrounding the fetus.
Doctors will develop a treatment plan after determining if the goiter is caused by hypothyroidism or hyperthyroidism (see Fetal Thyroid Disorders for more information). When diagnosed and treated properly, the prognosis is good for babies with a fetal goiter. However, if left untreated, congenital hypothyroidism is linked to neurodevelopmental delay.
Fetal Thyroid Disorders
In most cases, assessment of the maternal condition can help decide whether the cause of a thyroid goiter is fetal hypothyroidism or hyperthyroidism. Thyroid hormones are essential for brain development, and when a fetus is deprived of thyroid, it can have lasting, irreversible effects. Most cases of fetal hypothyroidism are caused by the use of antithyroid drugs for the treatment of maternal hyperthyroidism. This occurs when a pregnant mother takes antithyroid drugs for her own condition.
The less common condition of fetal hyperthyroidism can occur when the mother has uncontrolled hyperthyroidism, which is passed on to the baby. This can lead to preterm birth as well as a low birth weight for the baby. About 1% of mothers with active Graves’ disease, or who have a history of it, will have a baby with neonatal Graves’ disease. This requires hospitalization and support from intensive care, and the effects may be temporary or permanent. In its most severe forms, neonatal Graves’ disease is fatal for the baby.
Mothers with thyroid disorders can reduce the risk of fetal thyroid disorders by getting early prenatal care and working with their healthcare provider to monitor and manage their thyroid levels throughout their pregnancy.