Characterization of thyroid metastasis from clear cell renal cell carcinoma on ultrasonography: a report of three cases and literature review.

Introduction: Thyroid metastasis from clear cell renal cell carcinoma (ccRCC) is relatively rare, so ultrasound doctors lack experience with the disease, which can easily lead to misdiagnosis. We describe three cases of thyroid metastasis from ccRCC detected 12, 8, and 7 years after nephrectomy.
Case Presentation: The first patient, a 78-year-old woman, was admitted to our institution for hoarseness and progressive dyspnea. Ultrasonography revealed bilateral thyroid nodules and abnormal cervical lymph nodes. Fine-needle aspiration biopsy (FNAB) and core needle biopsy (CNB) of the thyroid was nondiagnostic. The other two patients, a 54-year-old man and a 65-year-old man, were admitted to our institution for a goiter pressing on the trachea. In each case, ultrasonography revealed a partially cystic nodule of the left lobe of the thyroid gland. Histological examination of three patients after thyroidectomy showed thyroid metastasis from ccRCC.
Discussion/conclusion: For patients with a history of ccRCC, long-term follow-up and routine thyroid ultrasonography should be performed. If a new thyroid nodule is found during the examination, metastases should be highly suspected. FNAB should be performed, even if benign ultrasound features seem to be in evidence. If the diagnosis of FNAB is incorrect and inconclusive, CNB should be performed.