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 cytology fig 3 above) 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).