Metastatic renal cell carcinoma in the thyroid gland: ultrasonographic features and the diagnostic role of core needle biopsy.

Metastatic RCC appears as oval-shaped hypoechoic solid nodules with well-defined smooth margins, no calcifications, and increased vascularity on ultrasonography. Characteristic US features along with a previous history of RCC should raise clinical suspicion, and CNB should be performed to make an accurate diagnosis.