Administrative Office
St. Joseph's Hospital Site, L301-10
50 Charlton Avenue East
HAMILTON, Ontario, CANADA L8N 4A6
PHONE: (905) 521-6141
FAX: (905) 521-6142 http://www.fhs.mcmaster.ca/hrlmp/
The electron microscope is an instrument in which the interaction of electrons with a specimen is used to provide information about that specimen. For diagnostic purposes, transmission electron microscopy (TEM) is most commonly used. The transmission electron microscope takes advantage of the wavelength property of electrons in order to increase resolution. In this manner, subcellular details not appreciated by the light microscope, become recognizable. Other interactions take place when an electron beam hits a sample; for example, secondary electrons are produced and can provide information about surface topography of a specimen. However, these interactions are less commonly used for diagnostic purposes.
In the 1980’s immunohistochemistry became increasingly important in the field of diagnostic surgical pathology and cytology. More recently, molecular techniques are playing a large role in diagnosis. The role of electron microscopy has seemingly diminished, however has not and probably never will be completely supplanted by these newer modalities.
TEM is a technique that provides direct visual evidence of a biological process, while the other techniques are indirect and in some instances non-specific. A number of studies have shown that TEM can have a major influence in diagnostic surgical pathology and/or cytology for neoplastic conditions in 18 to 57% of cases 1,2,3 . A similar claim can be made for non-neoplastic conditions, particularly for renal diseases.
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The electron microscopy unit at McMaster University Medical Center houses one transmission electron microscope, a combined transmission/scanning microscope with elemental analysis, a scanning electron microscope, 2 confocal microscopes as well as a strong technical support staff. A satellite laboratory with one transmission electron microscope is located at St. Joseph’s Hospital.
In the year 2000, the diagnostic electron microscopy unit received 950 specimens. Approximately 25% of these were kidney biopsies. In the field of renal pathology, TEM is invaluable for localizing glomerular immune deposits, for assessment of epithelial cells in cases of minimal change glomerulonephritis as well as for the assessment of glomerular basement membrane calibre in cases of Alport’s syndrome and Thin Basement Membrane disease. Approximately 25% of specimens were muscle biopsies. TEM is helpful in these cases for the assessment of mitochondrial disorders, certain metabolic disorders as well as specific entities such as oculopharyngeal muscle dystrophy in which characteristic filaments are seen at the electron microscopic level. The remaining specimens were a mixture of cases from a variety of sites. These included, nasal brush samples for ciliary abnormalities, liver biopsies from children for metabolic diseases, whole blood samples for platelet granule abnormalities as well as a variety of samples from neoplastic processes. While most tumours can be reliably sorted out by a combination of histochemistry and immunohistochemistry, for certain types of tumours electron microscopy may be the diagnostic modality of choice. For example, the chromophobe subtype of renal cell carcinoma and its’ variants can only be confidently diagnosed by demonstrating characteristic cytoplasmic vesicles by TEM. TEM is also used for virology investigations although these samples are handled directly by the microbiology section.

Figure 1.
Intra-abdominal small blue cell tumour in a young child showing dense core neuroendocrine granules in a cell process, characteristic of neuroblastoma.
Figure 2.
Whole mount preparation showing a normal spectrum of dense granules within one platelet.
The optimal primary fixative for TEM is glutaraldehyde. The amount of tissue required is minute compared to light microscopy – a tissue portion of 1mm 3 if representative is entirely adequate for TEM. Even in very small tissue samples, electron microscopy can be undertaken without compromising the material required for adequate light microscopic analysis. Tissue portions should be fixed immediately and kept at 4 0 C. Suboptimal preservation of tissue is one of the most common limiting factors in assessing ultrastructural details. A routine sample can be processed and ready for examination within 36 hours. If results are urgently required, samples can be rapidly processed and examined within one working day.
Considering that the Hamilton Regional Laboratory Medicine Program may handle between 45, 000 to 50,000 surgical pathology cases per year, the contribution of electron microscopy seems minor. However, electron microscopy does have something to offer – in the categories of glomerular disease, infectious disease (virology), metabolic disease, platelet granule abnormalities and ciliary dyskinesias. In the realm of neoplastic diseases, it may help to clarify inconsistent or confusing immunohistochemical results, it may assist in diagnosis of non-immunoreactive tumours, it can provide quality control for immunoperoxidase or immunofluorescence results, and lastly by direct visualization of a biological process, it can promote our understanding of new and/or controversial entities.
References
1. Expert Opinion: Electron microscopy for tumour diagnosis: is it redundant? Histopathology 1999; 35: 99-108.
2. Editorial: Diagnostic electron microscopy of neoplasms. Human Pathology 1998; 29: 1335-1338.
3. Frost AR, Orenstein JM, Abraham AA, et al. A comparison of the usefulness of electron microscopy and immunohistochemistry one laboratory's experience. Arch Pathol Lab Med 1994; 118: 922-926.
4.
Haas M. A re-evaluation of routine electron microscopy in the examination of native renal biopsies. J Am Soc Nephrol 1997;
8: 70-76.
Dr. K. Chorneyko
Hamilton Regional Laboratory Medicine Program
Anatomic Pathology Section
St. Joseph's Healthcare