Lingual Thyroid-CT

Case  description- ectopic lingual thyroid.

History- Young boy (16y )with swelling in neck.

Well defined hyperdense lobulated lesion at the base of tongue in midline extending to either side (left more than right)with moderate enhancement with small nonehancing foci & absence of thyroid gland in the normal location in thyroid bed- consistent with ectopic lingual thyroid gland with small nonehancing foci corresponding to thyroid nodules.

Teaching Points by – Dr MGK Murthy & Dr GA Prasad

CT Technician: Mr Venkat

1. Ectopic thyroid tissue can be found anywhere in the base of the tongue at the midline. The base of the tongue is the most frequent site of ectopic thyroid tissue, accounting for as many as 90% of reported cases. A lingual thyroid is more accurately described as an abnormally descended gland.
2. Other than lacking the characteristic bilobate shape, ectopic thyroid tissue appears identical to orthotopic thyroid tissue. At contrast material–enhanced CT, ectopic thyroid tissue appears as a well-circumscribed homogeneous avidly enhancing mass. At CT performed without contrast material administration, ectopic thyroid tissue demonstrates mildly increased attenuation (70 HU ± 10), a finding that is due to the intrinsic iodine content. Just as thyroid nodules appear as islands of low attenuation within the definitive thyroid gland, similar nodules within ectopic thyroid tissue can be a clue to the diagnosis.
3. Ectopic thyroid tissue or thyroglossal duct cysts of the base of the tongue are usually asymptomatic but can manifest with dysphagia, stridor, or dysphonia.
4. When a lingual thyroid is found, the usual thyroid bed location must be evaluated because orthotopic thyroid tissue will be absent 70%–80% of the time, and subsequent resection of the ectopic thyroid tissue will render the patient athyroid.
5. A radionuclide image of the thyroid obtained with technetium 99m pertechnetate, iodine 123 (¹²³I), or iodine 131 can be useful in identifying thyroid tissue, either in the usual thyroid bed or at ectopic sites; however, a normal thyroid gland can trap the majority of the radionuclide, making identification of small ectopic rests difficult. 

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