The FNA smears show an inflammatory process with features consistent with subacute (de Quervain's) thyroiditis:
- scattered benign reactive follicular epithelial cells
- prominent inflammatory background including multinucleate giant cells
- clusters of epithelioid histiocytes, consistent with granulomatous inflammation
Multinucleate giant cells and granulomas can be difficult to differentiate morphologically (see third image) but should not be confused theoretically:
- multinucleate giant cells are single cells with multiple nuclei, formed by the fusion of numerous macrophages (histiocytes)
- granulomas are aggregates of numerous 'epitheloid histiocytes' (activated macrophages).