Radioactive iodine imaging in the evaluation of thyroid nodules

Radioactive iodine imaging has been used extensively in the past for the evaluation of thyroid nodular disease. However, with the widespread use of thyroid ultrasonography and ultrasound-guided fine-needle aspiration, it has fallen out of favor. Expert guidelines advise against the routine use of radioactive iodine imaging in thyroid nodular disease except under specific circumstances. Nevertheless, most patients undergo radioiodine imaging before they come to see us. Although there are situations where such imaging is appropriate, it has been my experience that it is unnecessary most of the time.

A “hot” nodule does not usually need to be biopsied because it is almost never cancer. I say “almost never” because there are few absolutes in medicine. Malignant nodules that are hyperfunctioning have been reported. One of my colleagues here had such a case. The patient had a fully suppressed thyroid-stimulating hormone level and a hot nodule suppressing the rest of the thyroid gland. Rather than radioactive iodine therapy, she requested surgical resection. To everyone’s surprise, pathology revealed follicular cancer. However, such cases are very rare.

Of course, if a patient is hyperthyroid, then radioiodine imaging can be helpful. It is possible they might have a hyperfunctioning nodule or nodules which would not require biopsy. Another situation where radioiodine imaging may be of use is in the patient with a follicular neoplasm by fine-needle aspiration. If the nodule is hot, then it might not need surgical resection.

The problem is that few nodules are hyperfunctioning. Even though “cold” nodules are more likely to be cancer than “hot” nodules, up to 95% of thyroid nodules are either warm or cold. This means that in most situations, radioiodine imaging does not provide information that changes management. I have seen patients with hypothyroidism on long-term thyroid hormone therapy who had their levothyroxine withheld, just so radioiodine imaging could be performed before considering fine-needle aspiration. That does not make sense.

Performing radioiodine imaging in the evaluation of thyroid nodules adds significant cost to care. Khalid et al found that in the evaluation of a solitary thyroid nodule, radioiodine cost $24,554 compared with $1,212 for ultrasound-guided fine-needle aspiration per case of cancer identified.

For most patients, the evaluation of choice is thyroid ultrasound and if appropriate, ultrasound-guided fine-needle aspiration. As I wrote about in a previous post, in a nontoxic multinodular goiter with several large nodules I pay attention to those with characteristics that suggest higher risk of malignancy, and I consider biopsy in up to a total of four nodules.

Cooper et al. Thyroid. 2006;16:1-33.
Hegedus L et al. Endocrine Reviews. 2003;24:102-132.
Khalid A et al. Head & Neck Surgery. 2006;132:244-250.