Sonographic Presentation of Metastases to the Thyroid Gland: A Case Series

Incidental sonographic discovery of thyroid nodules is an increasingly common event. The vast majority is benign, and those that are malignant, are generally associated with an indolent course and low mortality. Sonographic scoring systems have been developed to help clinicians identify nodules that warrant prompt fine-needle aspiration cytology (FNAC), but they are based largely on experience with papillary thyroid cancers. We analyzed the performance of four scoring systems widely used for this purpose (American Thyroid Association Guidelines, American Association of Clinical Endocrinologists/American College of Endocrinology/Associazione Medici Endocrinologi Guidelines, European Thyroid Imaging Reporting and Data System, and Korean Thyroid Imaging Reporting and Data System) in patients whose nodules proved to be metastases from other solid cancers. Such nodules reportedly account for 0.2% to 3% of all thyroid malignancies. Each scoring system was used to assess retrospectively the malignancy risk and indications for FNAC of five patients' thyroid nodules that were ultimately diagnosed as metastases (from renal cell carcinoma, breast cancer, and lung cancer in two cases and esophageal cancer). The primaries identified in these cases are those most commonly reported to metastasize to the thyroid. In two cases, the thyroid metastases were the first sign of undetected neoplastic disease. Although sonography alone cannot distinguish thyroid metastases from primary thyroid malignancies, all four scoring systems classified the metastatic nodules as suspicious enough to require FNAC. The five cases accounted for 0.2% of those cytologically examined in our center. In most cases, cytology provided useful guidance for the subsequent management of these lesions, which differs from that of primary thyroid cancers and requires multidisciplinary input.