Hot thyroid nodules can sometimes be cancer.

A woman presented with hyperthyroidism. Her TSH was <0.01.  Radioactive iodine uptake and scan revealed an area of increased uptake on the right with suppression of the surrounding thyroid tissue consistent with a hyperfunctioning nodule (see figure #1).

Figure 1. Hyperfunctioning right thyroid nodule.

A thyroid ultrasound confirmed a nodule in this region.  The nodule was hypervascular, which would be consistent with a hyperfunctioning nodule. However, the nodule was also markedly hypoechoic with areas of calcification (see image #2). Because of the ultrasound findings, a fine needle biopsy was done, which identified a follicular lesion on cytology.

Because of the biopsy findings, the patient chose to undergo total thyroidectomy instead of radioactive iodine therapy. To everyone’s surprise, this nodule turned out to be a follicular thyroid cancer.  She subsequently was treated with radioactive iodine ablation. Since then, she has done well without evidence of residual cancer.

Most of us were taught that thyroid nodules that are hyperfunctioning or “hot” on radioactive iodine scan are very rarely — or almost never — cancer. This risk of cancer in a hyperfunctioning nodule is indeed rare. Because of this, guidelines suggest against biopsying hot nodules.  However, a recent literature review identified that of solitary hyperfunctioning thyroid nodules which were surgically resected, 3.1% were malignant.  Most were follicular or Hürthle cell cancers.

Figure 2. Ultrasound of hyperfunctioning thyroid nodule.

Some experts have advised against ordering thyroid ultrasound in hyperthyroidism because it would be unlikely to change management and would add cost and risk to patient care because it would result in unnecessary biopsies of benign thyroid nodules.

Although I agree with that opinion in general, I would not recommend primary care practitioners routinely order a thyroid ultrasound in the evaluation of every single patient with hyperthyroidism, I also believe there are exceptions. Furthermore, as I have posted before, when ultrasound is performed by an experienced thyroidologist, there are situations when ultrasound can be useful in evaluation of hyperthyroidism.

As clinicians, we must remember that even if the chances of something may very unlikely, that does not mean that it is absolutely impossible. Guidelines are meant only to be a guide; they are not rules written in stone.  The challenge for clinicians of course is to determine which nodules would benefit from further evaluation, while at the same time avoiding biopsying every single nodule “just because it’s there.”

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