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Head and Neck Imaging

Ectopic thyroid

thyroid tissue not in the normal anatomical location, i.e. in front of the proximal trachea. The thyroid gland is formed during embryonic life as an epithelial proliferation from the ventral pharyngeal wall; this is known as the medial thyroid anlage and the place where it arises later corresponds to the foramen caecum (at the border between the oral tongue and the tongue base). This medial thyroid anlage migrates downwards along the neck midline to its final position. Ectopic thyroid tissue can be found anywhere along this tract, but most commonly in the tongue. Patients with a lingual thyroid gland have no thyroid tissue in the neck in 7080% of cases (Fig.1). Ectopic thyroid is subject to the same diseases as the anatomically correctly positioned thyroid, such as nodular hyperplasia and rarely neoplastic degeneration (Fig.2). Development of a mass lesion is often the reason why these ectopic thyroids become symptomatic.

The existence of lateral thyroid anlage is controversial, but the existence of such structures may explain the occurrence of nonmidline ectopic thyroid tissue in the neck.

RH

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Fig.1

Sagittal T1-weighted image shows an inhomogeneously enhancing mass (arrow) in the tongue base: nodular hyperplasia in ectopic thyroid; no thyroid tissue was found lower in the neck.
Ectopic thyroid, Fig.1
Ectopic thyroid, Fig.2