Thyroid Case 7 Answers

1) What are the findings?

No identifiable uptake is seen in the expected location of the thyroid gland. There is a discrete focus of increased uptake in the oropharynx in the region of the tongue base.

2) How do you account for this?

These are the appearances of a lingual thyroid gland

3) What is the embryological explanation?

During normal development the thyroid anlage descends from the floor of the pharynx at the junction of the middle and posterior third of the tongue (the foramen caecum) to its normal position anterior to the trachea. In some cases (up to 7-10% in autopsy series), this process may be interrupted, leading to the presence of ectopic thyroid tissue. In 90% of such cases, the ectopic tissue is located in the tongue base, and in up to 70-80% of these cases the lingual thyroid is the only thyroid tissue.

4) How often is this associated with endocrine disturbance?

In up to 70% of cases the lingual thyroid does not secrete sufficient thyroid hormone, but the degree of hypothyroidism is usually mild (as in this case) and often asymptomatic. Up to 10% of cases will have overt congenital hypothyroidism (cretinism).

5) How else may this abnormality cause symptoms?

Though often asymptomatic, the lingual thyroid may enlarge and present with symptoms due to local mass effect in the tongue base in adult life. This is characteristically hyperdense on unenhanced CT due to its iodine content, and pertechnetate or radioiodine studies will confirm uptake within the mass as well as absence of normal thyroid tissue.

Contributed by Ian Hagan

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