Cytochemical investigations of phagocytes in thyroid gland cysts

Certain similarities in the cytoplasmic structure could indicate a histogenetic affinity between thyrocytes and pigmented macrophages in thyroid glands. On the other hand, the monocytogenic origin of macrophages in other organs in the body contradicts this assumption. We investigated these cells in smears of thyroid aspirates as well as in imprints, frozen sections and paraffin-embedded sections of freshly removed thyroid glands, using several cytochemical reactions and the usual panoptic stains. With the sodium-fluoride-inhibited alpha-naphthyl acetate esterase and tartrate-inhibited acid phosphatase reactions, the pigmented macrophages exhibited enzyme cytochemical patterns corresponding to those of blood monocytes or monocytogenic histiocytes but differing definitely from those of thyrocytes. Furthermore, we observed macrophages that exhibited a clearly monocytoid nuclear form and chromatin pattern in the interstitial space of the thyroid gland. These findings practically exclude a derivation of thyroidal pigmented macrophages from follicular epithelial cells and positively underline their derivation from blood monocytes.