**6.2 Radionuclide scan**

Although radionuclide imaging of thyroid gland has been done for a long time, resolution of this modality for thyroid nodule is far behind the ultrasonography [31]. So radionuclide imaging is not having much role in anatomic description of MNG. However radionuclide imaging is very useful in describing physiology of thyroid nodules. If TSH is subnormal, then ATA recommends a radionuclide thyroid scan to know whether nodules are hyperfunctioning ("hot," i.e., tracer uptake is greater than the surrounding normal thyroid), isofunctioning ("warm,"

**Figure 1.** *Nodule sonographic patterns and risk of malignancy.*

i.e., tracer uptake is equal to the surrounding thyroid), or nonfunctioning ("cold," i.e., has uptake less than the surrounding thyroid tissue) [32]. Since hyperfunctioning nodules rarely harbor malignancy, so cytologic evaluation is not required in hyperfunctioning nodules. Scan is also useful in distinguishing Graves' disease from (toxic MNG) Plummer's disease.
