Laser scanning confocal microscopy has been used to analyze cytological specimens for research purposes. However, for many pathologists, its application in diagnostic cytology still is terra incognita. In our laboratory, confocal microscopy has been used for seven years, mainly to solve problems in cervical cytology, in breast aspirates, and for endometrium cytology.

In contrast to histology where we can cut new sections from the block, the cytologic sample is often limited to one smear. Accordingly, when we wish to expand our diagnostic possibilities, we have to extract the desired additional information from that single smear. This is possible by first de-staining the original smear and subsequently re-staining it. In this article, we describe how we restain old slides with the fluorescent dyes Ethidinm Bromide and Eosin, a DNA/protein stain, resulting in staining patterns comparable to the diagnostic Papanicolaou and Giemsa methods in that mere is an optimal distinction between nucleus and cytoplasm.