Electron microscopy is a highly specialized method of cellular evaluation that can achieve resolution significantly > a conventional light microscope. Images are obtained through the differential interactions of electrons with the tissue components, and can achieve a resolution of 0.001 pm. The tissue sample is embedded into extremely hard epoxy plastic and is sectioned to very thin slices, 10 to 15x thinner than a traditional slice. The three types of electron microscopes are:
1. Transmission. The thin tissue section is impregnated with a heavy metal, which acts as a stain, while a beam of electrons is passed through the sample, allowing visualization of the small structures and intracellular components.
2. Scanning. A thin metal coating is applied to the surface of the sample, and the electron beam is sequentially scanned over points within the specimen, creating an almost threedimensional surface rendering.
3. Analytical. Allows the chemical composition of the components of the specimen to be determined.
Although electron microscopy can provide a significant amount of information regarding a tissue specimen, it is slow, very expensive, and labor intensive, and thus is primarily used as a research tool. It can be employed in selective clinical cases, where more information than can be provided with light microscopy is required to make a diagnosis. For tumor pathology, visualization of cellular ultrastructure can help in the classification of poorly differentiated neoplasms and other certain tumor types that exhibit specific subcellular hallmarks.