Ultra-rapid microwave-stimulated tissue processing with a modified protocol incorporating microwave fixation

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Abstract
To develop an ultra-rapid microwave (MW)-stimulated histoprocessing protocol that incorporates MW fixation and produces consistent, high quality sections. A range of fresh autopsy tissues was divided into three groups composed of equal numbers of small and large tissue blocks. Group 1 tissues were fixed for 8 hours in 4% buffered formaldehyde and processed in a conventional tissue processor through a 15-hour cycle. Group 2 tissues were processed in a MW histoprocessor according to the manufacturer's recommended protocol of irradiation in a proprietary reagent before embedding in paraffin. Group 3 tissues were processed with our protocol that incorporated the addition of MW fixation in 4% buffered formaldehyde and MW irradiation in isopropyl alcohol after irradiation in the proprietary reagent. The manufacturer's protocol resulted in 'grey' and 'wet look' artefacts in large tissue blocks. These artefacts did not occur in our protocol which produced sections that were indistinguishable from those obtained with conventional 23-hour processing. Histochemical and immunohistochemical stains were also indistinguishable and the tissue blocks cut very smoothly. The incorporation of an additional step to ensure adequate tissue fixation and one to ensure optimal dehydration and clearing resulted in a MW histoprocessing protocol that produced consistent results for both large and small tissue blocks. Paraffin-impregnated blocks can be produced very rapidly from fresh small and large tissue blocks in 45 and 100 minutes, respectively.