Ectopic thyroid is tissue not located antero-laterally to the second to fourth tracheal cartilages . In our case the right lobe appears normal (Fig. 1), with an empty left thyroid fossa (Figs. 2, 3).
The thyroid anlage appears in the embryo as a midline structure at the foramen caecum of the tongue. From here, it descends in the midline to reach its final position in the mid-neck [2, 3].
Ectopic thyroid tissue can be found within thyroglossal duct cysts, or anywhere along the course of the thyroglossal duct. Common sites include: foramen caecum (near embryological origin), base of the tongue, anterior tongue, submandibular region, larynx, intra-tracheal, intra-thoracic (mediastinum, heart, lung). .
Typically, ectopic thyroid presents as a painless midline neck swelling and can cause dysphagia, inspiratory dyspnoea and stomatolalia due to mass effect. It may coexist with eutopic thyroid or may be the only functioning tissue (in which case it must be preserved) .
Any pathology of the thyroid gland can involve ectopic tissue, including benign and malignant conditions.
Indirect clues for confirmation are: separate blood supply of the ectopic gland from extra-cervical vessels, no prior history of malignancy, and normal or absent orthotopic thyroid with no history of surgery .
Dual ectopy is a very uncommon condition in which two or more ectopic foci are present simultaneously.
In our case, the first mass is left sublingual (Figs. 4, 5, 10, 11), the second is mid-line, anterior to oropharynx (Figs. 6, 7, 12, 13), and the third is infra-hyoid, pre-laryngeal (Figs. 8, 9, 14, 15) in location. Sagittal (Fig.16) and coronal (Figs. 17, 18) reformatted images confirm above findings.
Sonography shows all three ectopic swellings have the same echogenicity as thyroid (Figs. 4, 6, 8), with normal vascularity on Doppler (Figs. 5, 7, 9).
CT shows mildly increased attenuation (around 110HU) due to intrinsic iodine content (Figs. 10, 12, 14) and homogeneous moderate contrast enhancement (Figs. 11, 13, 15) showing around 150HU attenuation.
Imaging delineates the extension and location of ectopic thyroid tissue, thus contributing to a better pre-surgical evaluation of these cases .
Other than lacking the characteristic bilobate shape, ectopic thyroid tissue appears identical to orthotopic thyroid tissue .
Asymptomatic euthyroid patients should be followed up.
Patients with high blood TSH levels and swelling should get replacement therapy, which can produce a slow reduction in size.
Obstructive symptoms due to mass effect require surgical intervention .