Thyroid Case 5 Answers

1) What are the findings?

There is a solitary, large, rounded focus of markedly increased uptake in the right lobe of the thyroid gland. Uptake in the remainder of the thyroid gland is suppressed.

2) What is the diagnosis?

These are the features of an autonomous hyperfunctioning (‘toxic’) thyroid adenoma

3) What proportion of cases of hyperthyroidism are caused by this condition?

In the order of 3-5%

4) What is the relevance of the size such lesions?

It is rare for an autonomous adenoma smaller than 2.5cm to cause thyrotoxicosis

5) What is the risk of malignancy in thyroid lesions with this pattern of uptake?

Leaving aside the thyroid hormone status, the incidence of malignancy in ‘hot’ thyroid nodules is very low (no more than 1-4% in various case series), and it would be even rarer for a thyroid carcinoma to cause clinical thyrotoxicosis. For this reason, thyroid uptake scintigraphy was often used to assess euthyroid patients with solitary thyroid nodules on the basis that if the lesion was truly hot (as opposed to ‘warm’ or ‘cold’) malignancy was very unlikely. However, the vast majority of solitary thyroid nodules are not hot, and the majority of cold nodules are still benign, so it is not a useful discriminatory test in this context and has fallen from favour

6) Are there any other conditions which can mimic this type of lesion on thyroid scintigraphy?

The appearance of a toxic adenoma can be mimicked by the absence of one lobe of the thyroid - either due to agenesis or surgical removal – with normal or increased uptake in the remaining tissue. If there is any doubt, ultrasound can be used for confirmation.

Contributed by Ian Hagan

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The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.