Microwave irradiation as a form of fixation for light and electron microscopy

Microwave irradition was used to fix a wide range of surgical and autopsy specimens as well as tissue from freshly killed rats. Although there appeared to be varying optimum temperatures of fixation for different tissues, from a practical standpoint, the heating to 58°C of tissues submerged in normal saline resulted in fixation of a quality comparable with that produced by conventional fixation to 10 per cent formalin. Microwave irradiation applied to tissues which had up to 1 h prior immersion in 10 per cent formalin also produced excellent preservation of cytomorphology, the time required for microwave fixation being no more than 150 s. This form of rapid heat fixation had no deleterious effects on special stains, sectioned as well as control fixed blocks and produced less shrinkage artefact than conventional formalin fixation. Immunocytochemical staining for more stable cytoplasmic antigens revealed no significant difference between microwave fixation compared with formalin fixation. The more labile membrane associated antigens of lymphocytes, however, were not preserved by either method of fixation. Microwave fixation was also found to be applicable to electron microscopy. Tissue samples immersed in 2.5 per cent glutaraldehyde and fixed in 90 s by irradiation to 50°C showed excellent preservation of ultrastructural morphology.