Electron microscopic assessment of smeared or imprinted specimens of solid tumours

The aim of this study was to develop a reliable method for preparation of smeared or imprinted cytology specimens for electron microscopic examination. Ten different solid tumours were studied. In each case one air-dried (Diff-Quik stained) and one alcohol-fixed (Pap stained) smear was prepared for diagnostic purposes. Simultaneously, a third smear or imprint was prepared for electron microscopy on a coverslip that was coated with poly-L-lysine and attached to a glass slide using double-sided adhesive tape. The smear or imprint was primary fixed in 2% glutaraldehyde in 0.1 M phosphate buffer, pH 7.4, for 2 hours. The coverslip was removed from the slide, placed in a glass petri dish and processed for electron microscopy. The smear/imprint on the coverslip was embedded in resin on a silicon embedding mould and allowed to polymerise for 8-12 hours. The coverslip was removed using liquid nitrogen and the block sectioned using standard techniques as for a monolayer. The specimens collected for electron microscopy using this technique yielded sufficient material for assessment with excellent tissue preservation producing good ultrastructural detail. Focal mechanical damage was seen in some specimens but diagnostic areas were always found within the block. As the smear/imprint can be regarded as a monolayer, the processing time can be reduced compared with solid tissue specimens. This technique ensures that well-preserved tissue is available for electron microscopy even when the sample size is very limited.