Tuesday, July 6, 2010

Discordant Thyroid Nodule

A thyroid nodule is considered discordant if it is hot on 99mTc and cold on 24-hour iodine imaging. Since 99mTc-pertechnetate is trapped but not organified, whereas iodine is both trapped and organified, a discordant nodule may either represent 1) reduced organification of iodine, or 2) rapid turnover of organified iodine.

A discordant nodule may represent benign lesions such as follicular adenoma/adenomatous hyperplasia or, in a small number of cases, thyroid cancer.

A patient with a hot nodule on 99mTc-pertechnetate imaging should get a 24-hour iodine scan.

References

Mettler FA and Guiberteau MJ. Chapter 5. In Essentials of Nuclear Medicine Imaging. Fifth Edition. Saunders, Philadelphia. 2006. p 83.

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