What is the role of radionuclide imaging in the evaluation of a solitary thyroid nodule?

Updated: Aug 19, 2020
  • Author: Daniel J Kelley, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Radionuclide imaging has been the mainstay in the evaluation of solitary thyroid nodule since 1939 when Hamilton and Soley demonstrated that malignant thyroid tissue concentrates less radioactive iodine than normal thyroid tissue. [14, 15] Thyroid nodules are further classified into cold, warm, and hot according to their ability to accumulate the radioactive isotope. Cold nodules are considered hypofunctional, whereas warm nodules are normal and hot nodules are hyperfunctional. Iodine-123 and technetium (99m Tc) are the most commonly used radionuclides for thyroid imaging.

The major limitation of thyroid radionuclide scanning has been its inability to distinguish between benign and malignant thyroid nodules with high accuracy. A review of published reports of radionuclide scanning reveals that 84% of solitary thyroid nodules are cold, 10% are warm, and the remaining 5% are hot. Malignant disease was found in 16% of cold nodules, 9% of warm nodules, and 4% of hot nodules. A cold thyroid nodule is more likely to be malignant, but most thyroid nodules are cold, including many benign lesions.

Other limitations of radionuclide scanning include an inability to delineate thyroid nodules at the periphery or isthmus of the thyroid gland and misinterpretation of the functional status of the thyroid nodule if normal functioning thyroid tissue overlies the cold solitary thyroid nodule or if the thyroid gland is asymmetric. Recent reports have shown some improvement in the diagnostic accuracy of99m Tc (MIBI) scanning when used in combination with FNAB. However, radionuclide scanning alone is not the most accurate technique to distinguish benign from malignant thyroid disorders.

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