USES AND LIMITATIONS OF ANCILLARY TECHNIQUES
APPLIED TO CYTOPATHOLOGY

Jeffrey S. Ross, M.D.

USES AND LIMITATIONS OF ELECTRON MICROSCOPY IN CYTOPATHOLOGY Although not considered a new technique, and having been applied to cytology specimens for some time, it is nonetheless important to include electron microscopy as an alternative complementary ancillary procedure to immunohistochemistry for the evaluation of cytologic specimens. Indeed when compared to IHC alone, when technically feasible, electron microscopy studies have been reported to have a more positive impact on establishing a cytologic diagnosis than IHC.87  For each individual patient, the relative potential contributions of EM and IHC must be assessed before they can be selected as ancillary procedures given the usual small sample size of cytologic specimens.88-89  For FNA specimens, EM may be diagnostic in 25-30% and helpful in 10-20% of cases. The major pitfalls in the use of electron microscopy in cytologic diagnosis are the availability of characteristic cellular material in small samples, the presence of necrosis and errors introduced by sub-optimal specimen preservation. FNA biopsies can be rapidly processed90  and has generally correlated with the results of immunocytochemistry on the same samples.91  Scanning electron microscopy has had limited clinical applications in cytopathology, but has been used to differentiate metastatic carcinoma from benign and malignant mesothelial cells based on the surface pattern of the microvilli.92