Artefacts in electron microscopy: ultrastructural features of chrysiasis.

Eleven cases of chrysiasis have been studied ultrastructurally and by electron probe microanalysis. Tissue samples were examined both with and without osmium and uranyl acetate staining. There was a significant morphological difference in the appearance of the gold deposits within aurosomes between the two groups. The untreated group showed finely granular deposits, often arranged in a linear fashion. Aurosomes from samples treated with osmium and uranyl acetate showed more electron-dense deposits and star-like formations. We propose that treatment of the tissue with osmium and uranyl acetate causes a change in the electron microscopic appearance of aurosomes, including the formation of the characteristic star-like aurosomes.