Hidden in Plain Sight: Metastatic Renal Cell Carcinoma Masquerading as Multinodular Thyroid Disease.

Metastases to the thyroid gland are uncommon, with renal cell carcinoma (RCC) representing a rare but clinically significant occurrence. RCC may metastasize after a prolonged dormancy and remain clinically silent for years before detection. We present a case of a 61-year-old man who initially presented with hematuria. Imaging at the time revealed RCC confined to the kidney. Several years later, during surveillance imaging for newly diagnosed prostate cancer via prostate-specific membrane antigen (PSMA) positron emission tomography (PET), bilateral thyroid nodules were incidentally detected. Histopathological examination of the resected multinodular thyroid revealed an unexpected finding of metastatic RCC, initially masquerading as a primary thyroid neoplasm. Awareness of RCC's propensity to masquerade as a primary thyroid tumor is paramount for the surveillance and management of patients with a history of RCC.