Definition: Goiter represents an enlargement of the thyroid gland.

Prevalence: Rare.

Etiology: Fetal goiter can be associated with hyperthyroidism, hypothyroidism or an euthyroid state. Goiter associated with hyperthyroidism can be the result of iodine excess or deficiency, intrauterine exposure to antithyroid drugs or congenital metabolic disorders of thyroid synthesis.

Ultrasound features: The goiter is manifested as a solid, anteriorly located symmetric mass, that may result hyperextension of the fetal head. Polyhydramnios is common due to mechanical obstruction of the esophagus.

Ultrasound picture of a large fetal goiter (arrow)

Prognosis:  Goiter may cause dystocia by extension of the fetal head during the process of labor. It can also cause upper airway obstruction, leading to acute respiratory failure. The prognosis depends on the basic cause of the goiter. Most cases of fetal goiters occur in women with a history of thyroid disease. Fetal blood sampling can aid in determining fetal thyroid status, especially in women  suffering from Grave's disease where a transplacental transfer of drugs or thyroid-stimulating antibodies may result in fetal goiter. Maternal therapy usually corrects fetal hyperthyroidism. Direct  fetal therapy in cases of fetal hypothyroidism is available either by amniocentesis or by cordocentesis. Cases of disappearance of goiters after direct fetal therapy have been reported[1].

Reference:

[1] Abuhamad, A.Z., Fisher, D.A., Warsof, S.L., Slotnick, P.G, Pyle, S.-Y. Wu, Evans, A.T. Antenatal diagnosis and treatment of fetal goiterous hypothyroidism: case report and review of the literature. Ultrasound Obstet Gynecol 1995; 6:368-371.