Thyroid Case 1 Answers

1) Is thyroid uptake normal?

Yes. This patient had no clinical evidence of thyroid disease. The normal bilobed appearance of the thyroid gland is demonstrated with the two lobes connected by an inferior isthmus. The slight asymmetry of the two lobes seen here is a frequent finding in normal individuals.

2) Identify structures A and B. Why may the patient be asked to drink a glass of water prior to imaging?

A and B represent the right and left submandibular salivary glands. Pertechnetate is handled by the salivary glands in the same way as chloride ions and is secreted into saliva. Such salivary activity may cause a misleading appearance when in the pharynx or upper oesophagus. This problem can be avoided by asking the patient to drink some water prior to imaging.

3) Where else may physiological pertechnetate uptake be seen in the body?

In addition to the salivary glands, pertechnetate is normally taken up by the gastric mucosa, choroid plexus of the brain, and lactating breast. Some pertechnetate is excreted in the urine and thus urinary tract activity may also be seen.

4) Which other views may be acquired on thyroid uptake studies?

It is routine to perform an additional anterior view with a sternal notch marker (e.g. Cobalt-58) to assess any retrosternal extension of thyroid tissue. Oblique views can be useful in distinguishing thyroid activity from oesophageal activity, and are particularly important in the accurate assessment of thyroid nodules. A lateral view is helpful in the localisation of possible ectopic thyroid tissue.

5) Which other agents may be used for thyroid scintigraphy? What are their advantages and disadvantages?

Iodine-123 and -131 are also available for thyroid imaging. Like pertechnetate they are actively imported into the thyroid but are in addition organified and stored in the thyroid. I131 emits beta particles and high energy (364keV) photons with a half-life of 8 days. The resulting poor image quality and high patient dose mean it is now used almost exclusively for therapy. I123 is a much better imaging agent, emitting 159keV photons with a half-life of 13 hours. It is regarded as the ‘gold standard’ for thyroid imaging, particularly for quantitative studies. However, as a cyclotron product it is much more expensive and less readily available than pertechnetate.

6) Other than thyroid pathology, what patient factors may interfere with thyroid uptake?

Anything which increases the blood iodine pool will reduce thyroid tracer uptake, including some foods (e.g. kelp), drugs (e.g. amiodarone, some cough medicines) and iodinated intravenous contrast agents (may reduce thyroid uptake for 1-2 months)

Contributed by Ian Hagan

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