Electron microscopy renders the diagnostic capabilities of cytopathology more precise: an approach to everyday practice

Cytology is a powerful diagnostic tool but to make definitive diagnoses, the use of ancillary techniques is imperative. By combining immunohistochemistry (IHC) and electron microscopy (EM), cytologic diagnoses can be as precise as those of surgical pathology. In the authors' daily practice of cytopathology they use all ancillary techniques available to them: histochemistry, IHC, EM, flow cytometry, and molecular pathology. IHC is frequently used as an ancillary technique in their daily practice but EM is many times their technique of choice. By the use of EM the authors can make specific final diagnoses, make the diagnosis more definitive, narrow the differential diagnosis, or determine the origin of a neoplasm with unknown primary site. Specimens obtained by fine-needle aspiration as well as all body fluids are suitable for EM. The limiting factor is to obtain the appropriate material with the diagnostic cells for ultrastructural examination. The common diagnostic dilemmas in the everyday practice of cytology are the following: mesothelioma vs. adenocarcinoma, neuroendocrine differentiation or not, the distinction of melanoma from adenocarcinoma and sarcoma, hepatocellular carcinoma vs. adenocarcinoma, and the origin of adenocarcinomas of unknown primary. The authors discuss how they approach these diagnostic problems in their everyday practice and how they incorporate EM in solving them.