Testing Methods

Morphological techniques include cytological studies (the evaluation of individual cells in fluids) and histological studies (the evaluation of cells in their tissue context). The latter involve light microscopy with routine and special stains, electron microscopy, histochemistry, and immunohistochemistry. Typical methods of fixation and staining for each technique are summarizedin Iable.25-7 . Ancillary studies that supplement the armamentarium of morphological techniques include microbiology (e.g., bacterial, viral, fungal cultures), cytogenetics (e.g., karyotype analysis), molecular genetics (e.g., polymerized chain reaction), and biochemical analyses.

The choice of morphological and ancillary techniques depends on the nature of the lesion and the available material. Although most pathological diagnoses are made on sections of formalin-fixed paraffin-embedded tissues stained with hematoxylin and eosin or a comparable general tissue stain, some diagnoses require other stains to be used on the paraffin-embedded tissues or even other methods of tissue handling and fixation (freezing, glutaraldehyde fixation and plastic embedding for electron microscopy, submission of unfixed tissues in special handling media for cytogenetic or microbiologic studies, etc.). Before fixation, tissue should be divided and processed appropriately for these studies. Consideration of the expected diagnosis, obtained from the preoperative workup or from intraoperative frozen section, is essential in the planning and optimal handling of the diagnostic brain biopsy. Familiarity with a particular institution's manual of laboratory procedures that list recommendations for handling tissues for specific test and communication with the neurosurgeon and pathologist in advance of the biopsy procedure are necessary to avoid inappropriate handling of valuable specimens.

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