Multinucleated giant cells in fine-needle aspiration of thyroid nodules: their diagnostic significance.

Multinucleated giant cells (MNGCs) are reported in many thyroid lesions. This study examines whether their quantity and quality can help in the differential diagnosis. All fine-needle aspirations (FNAs) of the thyroid with a "significant" number of MNGCs were reviewed from 1995 -1998. There were 23 cases (<1% of thyroid FNAs): 8 papillary carcinomas (PC), 4 subacute thyroiditis (ST), 3 granulomas, 7 adenomatous goiters (AG), and one Hurthle-cell adenoma (HA). MNGCs with dense cytoplasm were seen exclusively in PC, ST, and granulomas. They had angulated shapes. They were most numerous, largest, and with the highest number of nuclei in ST and granulomas. MNGCs with foamy cytoplasm were seen in AG and HA and 80% of the other cases (PC, ST, and granulomas). In PC, rare MNGCs had intranuclear inclusions and grooves. The accompanying cell population was characteristic of each disease. The quantity and quality of MNGCs in thyroid FNA may be helpful in narrowing the differential diagnosis. Diagn. Cytopathol. 1999;21:307-312.