Thyroid gland ectopias.
Failures of descent of the medial anlage of the thyroid and incomplete obliteration of its vertical tract lead to midline or near-midline ectopias such as lingual thyroid and thyroglossal cysts. Each poses special diagnostic and therapeutic considerations. "Ectopias" of the thyroid gland lateral to the carotid artery and jugular vein, however, cannot be readily explained by current embryological information. In these instances, and especially for intranodal thyroid tissue, a metastasis from an occult thyroid primary is the mandatory first consideration.