Head & Neck | Fetal neck masses
Abnormalities of the fetal neck are uncommon and may be serious. The most important abnormalities are cystic hygromas, neck neural tube defects (occipital encephalocele, cervical meningomyelocele) and neck tumors (cervical teratomas). Rarely, a fetal thyroid enlargement (goitre) may be detected. Information from the ultrasound on whether the mass is cystic or solid, as well as its position and extent, can help to establish the diagnosis.
- The outcome from abnormalities of the fetal neck, both in the short and long term, will depend on the actual diagnosis.
- Some of these abnormalities are serious, as they are associated with other conditions.
- After an anomaly is detected, serial scans are performed to update findings, as this may affect the prognosis and location and mode of delivery.
There are four important abnormalities of the fetal neck:
This is a lymphatic abnormality which forms a cystic mass at the side or back of the neck. It is often detected at the 11-14 week ultrasound. Cystic hygromas are often associated with chromosomal or heart abnormalities, syndromes such as Noonan syndrome and hydrops (generalized fluid accumulation in the fetus). The most common chromosomal abnormality is Turner syndrome (45, XO) which occurs in about 75%, but a minority have trisomy 21 (Down syndrome) or trisomy 18 (Edward’s syndrome).
Chromosome testing and fetal heart ultrasound (echocardiography) are recommended and management depends on the diagnosis. Cystic hygromas with hydrops have a very poor prognosis, whereas without hydrops, they usually regress completely.
Neck Neural Tube Defects
Occipital encephalocele results from a skull defect and herniation of brain tissue through the defect. It is rare, occuring in between 1 in 5,000 and 1 in 10,000 pregnancies. There are associated abnormalities in the brain and skull. The outlook is generally poor and the majority of survivors will have significant intellectual disability.
Cervical meningomyelocele is a rare congenital abnormality in the cervical region of the spine. It is an opening in the fetus’ spinal column that exposes the spinal cord and surrounding tissue. While this condition is not life-threatening, it can lead to children being born with significant disabilities.
These are rare tumors. The majority are benign but they can be large and are associated with excessive amniotic fluid because of compression of the esophagus. On ultrasound assessment, the tumors are usually solid with cystic components and can produce hyperextension of the fetal neck. Urgent treatment is required at delivery so that an airway can be established to prevent respiratory distress.
Thyroid Enlargement / Goitre
Goitres can be associated with hypothyroidism (most common) or hyperthyroidism. Congenital hypothyroidism occurs in about 1 in 5,000 live births and is usually caused by treatment with antithyroid drugs for maternal hyperthyroidism. The fetal thyroid is visibly enlarged on ultrasound. The prognosis depends on the cause and can be associated with excessive amniotic fluid from neck compression.
An accurate diagnosis is important as it influences management and treatment of fetal neck masses.
In rare cases, fetal therapy may be an option. In the majority of cases, urgent treatment may be needed at birth.