Role of fine-needle aspiration cytology in the diagnosis of secondary tumors of the thyroid--twenty years' experience.

Secondary tumors of the thyroid, presenting as thyroid nodules although rare, have been documented in literature. This study highlights the frequency, primary sites, and the role of fine-needle aspiration cytology (FNAC) in evaluating secondary tumors of the thyroid at a tertiary care hospital. There were 24 documented cases of secondary tumors of the thyroid from 1982 to 2002 (20 years). The aspirates and histology slides of all these cases were reviewed and the findings noted. On FNAC, 17 cases were diagnosed as secondary tumors, 3 as primary, and in 4 cases it was difficult to categorize the tumors as either primary or secondary. In 12 out of 24 cases, the primary tumor was seen to arise in the larynx (9), and in other sites anatomically close to the thyroid including the trachea (1), and the esophagus (2). Metastases from distant organs were also observed. Secondary tumors of the thyroid are rare and should be suspected in patients when the FNAC shows cytological features not seen in primary thyroid tumors. FNAC alone was required to accurately diagnose secondary tumors of the thyroid in a majority of cases (17/24); however, in some cases ancillary techniques may be required for a definite diagnosis. 2006 Wiley-Liss, Inc.