Electron Microscopy of Needle Biopsies
of a Retroperitoneal Mass

Leiomyosarcoma of retroperitoneal and possible adrenal gland origin

Discussion:

As this case illustrates, using cytopathology in combination with electron microscopy in the evaluation of fine-needle aspiration biopsies (FNABs) significantly contributes to patient management. In less than 48 hours, ultrastructural examination of fragments of tumor tissue from both FNA and core-needle biopsies provided a specific diagnosis of leiomyosarcoma. Coupled with the ultrasound and CT scanning information of an invasive tumor, the patient was immediately transferred to the Medical Oncology Service and chemotherapy initiated.

In a retroperitoneal lesion such as the present case, thought to represent an adrenal tumor, electron microscopy readily eliminated such diagnoses as cortical carcinoma or pheochromocytoma. Furthermore, ultrastructural examination can be particularly helpful in the differential diagnosis of spindle cell tumors, whether of soft tissue or retroperitoneal origin (1,2). In FNABs, identification of sarcomas with their specific subcellular diagnostic features particularly benefits from electron microscopy. Note should be made of the considerable battery of antibodies used in the investigation of this case; in such circumstances, electron microscopy is not only cost-effective but the immunohistochemistry was actually unnecessary. This case also illustrates a potential pitfall of immunohistochemistry, false-negative results such as occurred with staining for vimentin. Difficulties in interpretation may result when either an expected intermediate filament is not expressed or the molecule in neoplastic cells is so modified that it fails to be detected by the monoclonal antibody; these and other problems associated with immunohistochemistry are the topic of a recent editorial (3).

Finally, quantitative studies comparing the diagnostic efficiency of immunohistochemistry and electron microscopy are beginning to appear (4-6), one of which focuses on FNABs (5). In such reports of ancillary diagnostic techniques, electron microscopy outranks immunohistochemistry in terms of diagnostic proficiency.

References:

1. Fisher C: The value of electronmicroscopy and immunohistochemistry in the diagnosis of soft tissue sarcomas: A study of 200 cases. Histopathology 1990;16:441-454.
2. Yazdi HM, Dardick I: Diagnostic Immunocytochemistry and Electron Microscopy. Guidelines to Clinical Aspiration Biopsy. Igaku-Shoin, New York, 1991.
3. Erlandson RA, Rosai J: A realistic approach to the use of electron microscopy and other ancillary diagnostic techniques in surgical pathology (editorial). Am J Surg Pathol 1995;19:247-250.
4. Frost AR, Orenstein JM, Abraham AA, Silverberg SG: A comparison of the usefulness of electron microscopy and immunohistochemistry - one laboratory’s experience. Arch Pathol Lab Med 1994;118:922-926.
5. Oreilly PE, Bruecker J, Silverman JF: Value of ancillary studies in fine needle aspiration cytology of the lung. Acta Cytol 1994;38:144-150.

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