Before the advent of ultrasonography and needle biopsy of the thyroid gland, thyroid scan was frequently used together with the thyroid function tests and radioactive iodine uptake.
With the presence of ultrasonography and needle biopsy of the thyroid, my usual indications for thyroid scan are now confined to when there is a need to firm up a clinical suspicion or diagnosis of an autonomous functioning thyroid nodule (solitary thyroid nodule with pulse rate of over 90 beats per minutes, elevated FT4 and decreased TSH levels). This entity is not common in my clinical practice.
I don’t do thyroid scan to check whether a nodule is hot or cold. If there is a need, I rely on ultrasound and needle biopsy to determine whether a nodule is benign or malignant. In yesteryears, the presence of a cold nodule usually swayed the surgeon to operate on the basis of a significantly high incidence of malignancy (which was actually only in the vicinity of 10-15% percent; majority are still benign). I don’t use the presence of cold nodule on thyroid scan as a basis for a clinical diagnosis of thyroid malignancy. I now rely on a needle evaluation and aspiration biopsy to determine whether a thyroid nodule is benign or malignant.
In patients who had previous thyroid operations especially those done by other surgeons in which I have to do a completion thyroidectomy, I rely more on thyroid ultrasound than on thyroid scan to determine how much was left behind and where to look for the remaining thyroid gland.
Thyroid scan of yesteryears
Modern pictures of thyroid scan
Autonomously functioning thyroid nodule on the left
Difference between hot and cold nodules