Subacute (de Quervain's) thyroiditis.

Figure 1. Intermediate-power microscopy shows the eosinophilic colloid-filled follicles at the periphery. In many follicles in the center, the epithelium has been replaced by the inflammatory reaction and the colloid is reduced or absent. Microabscess formation with foreign-body-type giant cells can be seen. Figure 2. A: The colloid is engulfed by the ring of foreign-body-type giant cells with associated fibrosis. B: A microabscess is made up of neutrophils in association with foreign-body-type giant cells.