(A) Anterior and oblique views from an iodine 123 thyroid scan demonstrate a cold focus at the left mid-to-upper lobe (circle) with otherwise homogeneous uptake. A linear focus extending superiorly from the midline represents a pyramidal lobe (arrow). (B) Early and 24-hour thyroid radioactive iodine uptake (RAIU) values are significantly elevated (normal, 10–30% at 24 hours).

Differential Diagnosis

•  Graves disease plus an indeterminate cold nodule: In the setting of hyperthyroidism, elevated thyroid uptake in a diffuse pattern almost always indicates Graves disease. The superimposed cold nodule is indeterminate and carries a 15 to 20% risk for malignancy.

•  Focal thyroiditis: This can simulate a cold nodule on thyroid scan but will not have significantly increased thyroid uptake values.

•  Toxic nodular goiter: This can have moderately increased thyroid uptake values, but the nodule(s) are hot and the rest of the gland is suppressed.