What percentage of cold thyroid nodules are malignant?
**Core Concept**
The question is testing the student's knowledge of the malignant potential of thyroid nodules, specifically cold thyroid nodules. Cold thyroid nodules are non-functioning thyroid nodules that do not take up radioactive iodine on a thyroid scan. The majority of these nodules are benign, but a small percentage can be malignant.
**Why the Correct Answer is Right**
Only a small percentage of cold thyroid nodules are malignant, typically less than 5-10%. This is because the majority of thyroid cancers arise from the follicular epithelium, which can take up radioactive iodine and appear as "hot" nodules on a thyroid scan. Cold nodules are more likely to be benign cysts, adenomas, or fibrosis. However, some thyroid cancers, such as follicular and papillary thyroid cancer, can arise from cold nodules.
**Why Each Wrong Option is Incorrect**
* **Option A:** 20% - This is too high, as the majority of cold thyroid nodules are benign.
* **Option B:** 3% - While this is closer to the correct answer, it is still slightly too high.
* **Option C:** 1% - This is too low, as some cold thyroid nodules can be malignant.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the risk of malignancy in cold thyroid nodules increases with age, particularly in women. A fine-needle aspiration biopsy is often necessary to determine the nature of a cold nodule.
**Correct Answer: C. 5%**