Analysis of Fine Needle Aspiration Cytology and Ultrasonography of Metastatic Tumors to the Thyroid.

Cytologic diagnosis of the metastatic tumors to the thyroid is important in the management of the patients. There have been rare reports analyzing fine-needle aspiration (FNA) cytology of metastatic tumors to the thyroid. This study examines comprehensive cytologic findings of metastatic tumors to the thyroid with radiologic findings. The FNA cytology slides obtained from 12 cases with metastatic tumors of the thyroid; lung cancer (n=5), tongue and tonsil cancer (n=3), esophageal cancer (n=2), and breast cancer (n=2) were reviewed. Radiological study showed single mass with heterogeneous texture or multiple masses without calcification. Metastatic tumor was easily considered in a differential diagnosis of FNA cytology because they had peculiar cytological features which were not seen in primary thyroid tumor. The smear background varied from predominantly necrotic, bloody, and inflammatory to colloid. The aspirates exhibited a mixture of benign follicular cells and malignant cells in 6 cases. The characteristic cytoplasmic features of the tumor cells, such as keratin, mucin and melanin, were found in 9 cases. Although some cases mimic primary thyroid neoplasm, a careful examination of the cytological characteristics may help cytopathologists to recognize a metastatic tumor in the thyroid by FNA, and may help the clinicians to establish a proper treatment plan.