What proportion of focal thyroid nodules are cancerous?
Approximately 20% of all focal nodules that are biopsied are neoplastic, with the majority due to benign follicular adenomas and the minority due to thyroid malignancy. Follicular adenomas are much more common in women and are usually incidentally detected when the patient is undergoing imaging of the thyroid for another reason.
On US, follicular adenomas may be entirely solid or have internal cystic regions, have a well-defined capsule, and tend to have marked vascularity throughout the nodule. They are not considered to pose a risk of malignancy although a small percentage may become hyperfunctioning and lead to hyperthyroidism