A fetal goitre is an enlargement of the thyroid gland in utero. It can occur with either hyper- or hypothyroidism (and in isolated cases of euthyroidism ⁸).

Pathology

The mechanism depends on whether the underlying cause is hyper- or hypothyroidism. 

Associations

• maternal Graves disease with propylthiouracil (PTU) treatment ¹

• Pendred syndrome

• polyhydramnios: from impaired swallowing ²

Radiographic features

Ultrasound

While antenatal detection is rare, once detected, it is important to evaluate fetal thyroid function in order for early treatment to be initiated if necessary.

A fetal goitre may be seen as a relatively homogeneous anterior fetal neck mass. There is also evidence of polyhydramnios. If the goitre is very large the neck may appear hyperextended.

Some investigators have attempted to assess the hyper- or hypothyroid status relying on sonographic features ⁷:

• hypothyroid goitres  

  • more likely to have a peripheral vascular pattern on colour Doppler

  • may have evidence of delayed bone maturation

  • may be accompanied by increased fetal movement

• hyperthyroid goitres 

  • more likely to have central vascularisation

  • may have evidence of a fetal tachycardia

  • may have evidence of advanced bone maturity

Treatment and prognosis

Treatment will, again, depend on whether the fetus is hyper- or hypothyroid.

Complications

• hydrops fetalis: from increased vascular shunting within the goitre

• development of a fetal tachycardia

• cervical dystocia: from the extended position of the fetal head in labour