The Contribution of Electron Microscopy to the Differential Diagnosis of Tumors

Abstract

Summary From these selected examples of our own experience, as well as from the results obtained by others (Rosai and Rodriguez, 1968), it must be concluded that electron microscopy can, on occasion, be a significant aid in the accurate diagnosis of various neoplasms. While optimal fixation of tissues processed for electron microscopy produces excellent results with good cytologic preservation of the cellular organelles and extracellular components, the use of electron microscopy should not be excluded because the tissue has been fixed in formalin or routinely embedded in paraffin for light microscopy. Today, rapid fixation of minced tissue in glutaraldehyde with postfixation in osmium tetroxide provides the best preservation of the fine structure of cells (Sabatini et al., 1963). However, good results can be obtained if, instead of glutaraldehyde, minute pieces of tissue are originally fixed in buffered formaldehyde and processed according to the standard electron microscopic techniques. Furthermore, larger fragments of tissue fixed in formaldehyde and stored for prolonged periods of time can still be useful for diagnostic electron microscopy since many of the ultrastructural features used for diagnostic purposes are preserved even with prolonged formaldehyde fixation. Carson et al. (1973) have shown that phosphate buffered commercial formaldehyde provides satisfactory fixation for routine light and electron microscopy. In the past many investigators have suggested fixatives as substitutes for the usual light microscopy fixatives which could enhance ultrastructural preservation (Chambers et al., 1968). In our experience, all of these have been either financially unfeasible for large scale fixation or have provided suboptimal fixation for light microscopy specimens. Recently McDowell and Trump (1975) have introduced the use of a phosphate buffered mixture of 4% commercial formaldehyde and 1% glutaraldehyde as a fixative which, according to these investigators, gives satisfactory preservation for routine automated histologic processing and for electron microscopic studies. But, it should also be re-emphasized that electron microscopy is possible not only on tissue that has been fixed in formalin and processed shortly thereafter, but even when it had been stored in formalin for prolonged periods of time, or on tissue embedded in paraffin. A method of reprocessing for electron microscopy of formalin-fixed wet tissue, or formalin-fixed and paraffin embedded tissue, has been described (Zimmerman et al., 1972), as well as a method by which histologic sections of paraffin-embedded formalin-fixed postmortem specimens are prepared for electron microscopic study by what is called the “open-face” embedding (Rossi et al., 1970).