Thyroid Gland - Cyst, Congenital

Cysts found in the thyroid and adjacent parathyroid represent embryonal rests and may be lined by flattened or ciliated epithelium (Figure 1 and Figure 2). When filled with keratinized material (Figure 3 and Figure 4), they are typically considered to be ultimobranchial cysts; however, ultimobranchial cysts can sometimes be lined by ciliated epithelium. Thyroglossal duct cysts, on the other hand, are usually centrally located and lined by multilayered thyroidogenic epithelium. However, given the difficulty in precisely classifying cysts, the more generic nomenclature of “congenital cyst” is preferred. Since chronic studies may incorporate in utero exposures, developmental alterations related to treatment could influence the presence and ultimate appearance of congenital thyroid cysts.