Lipid-rich residual bodies in the human thyroid gland: ultrastructural, histochemical, and morphometric study.

Eleven samples of surgical and autopsy thyroid tissue were studied by classical histology, histochemistry, immunohistochemistry, light microscope quantitation and transmission electron microscopy in order to characterize lipid-rich residual bodies (LRRBs) previously reported in human myometrium. The following observations were made: 1) LRRBs were found largely in follicular epithelial cells; 2) they had exactly the same histochemical, immunohistochemical and ultrastructural characteristics as LRRBs from myometrium; 3) they had a distinctive distribution and morphology compared with lipofuscin; 4) a lysosomal nature was confirmed by their content of acid phosphatase and cathepsin D; 5) they were virtually absent from both the new-born thyroid and from thyroid carcinoma; 6) there was a statistical linear correlation between LRRB frequency and patient age. In conclusion, LRRBs have been demonstrated in an extra-uterine location, and are confirmed as residual lysosomes, probably having been involved in lipid metabolism.