Lipid-rich residual bodies in human myometrium: qualitative observations

Uterine leiomyomata and histologically normal myometrium were examined by light and electron microscopy. All myometrial samples contained smooth muscle cells with distinctive cytoplasmic inclusions located at the nuclear poles. These were seen in only one case in routine paraffin wax sections, where they appeared as clear vacuoles, but they were more obvious in epoxy resin sections stained with toluidine blue. Staining with Oil Red O and for acid phosphatase was positive at the site of the vacuoles. In ultrathin sections, these structures possessed a single membrane and contained abundant lipid droplets, with a sparse, coarsely granular matrix. They were designated as lipid-rich residual bodies. Such organelles were all but absent from leiomyomata. Lipid-rich residual bodies with the features described here have not been studied in detail before in smooth muscle cells of the human myometrium. The possibility that they arise from the cyclical stimulation of lipid synthesis by ovarian hormones is discussed.