General Principles of Cytopathology
Brian Collins
I. INTRODUCTION. Cytopathology has developed into a discipline that examines cellular elements from throughout the body collected by a wide variety of methods and procedures. It shares with other anatomic pathology disciplines a morphologic study of cells utilizing patterns and cellular features to identify specific pathologic conditions. Cytopathology provides diagnostic information in a wide variety of clinical settings, and can thus be used to guide patient management both at the time of initial diagnosis and during the course of treatment. In broad terms, there are three main areas of cytopathology, specifically (i) gynecologic/Pap slides, (ii) nongynecologic (Non-Gyn), and (iii) fine needle aspiration (FNA).
The utility of cytopathology is underscored by the fact that virtually all ancillary laboratory techniques used in surgical pathology can also be performed on cytology specimens.
A. Immunocytochemistry. Special stains are commonly applied to cytologic samples, often to confirm the morphologic diagnosis, to help in determining the possible primary sites of a tumor, or to determine the presence of specific prognostic markers. In general, cell block sections are preferred for immunocytochemical staining because most laboratories have experience in processing the formalinfixed, paraffin-embedded (FFPE) tissue sections that are generated from cell blocks.
B. Flow cytometry. In the presence of a lymphocyte-rich sample, the possibility of a lymphoproliferative process may need to be addressed by flow cytometry. Body fluids, particularly effusions, are amenable to this type of analysis.
C. Molecular genetic methods. Cytological preparations, including fluid specimens, brushings, washings, and scrapings, are suitable substrates for molecular analysis. Regardless of the method used to process samples (e.g., whether air dried, ethanol fixed, or used to produce a cell block) it is possible to extract nucleic acids that can be analyzed by a wide variety of genetic assays, including polymerase chain reaction (PCR), DNA sequence analysis, gene expression analysis, and fluorescence in situ hybridization (FISH).
II. GYNECOLOGIC/PAP SLIDES. The “Pap test” is the most successful cancer screening test in medicine. After the wide introduction of the Pap smear, the incidence of cervical carcinoma dropped significantly and it remains the mainstay of screening women for cervical carcinoma. Standardized terminology and categorizations for the Pap smear have been developed (The Bethesda System for Reporting Cervical Cytology. New York, Springer-Verlag, Inc.; 2004). The Bethesda Reporting System for Cervical Smears is covered in more detail in the cytopathology section of Chapter 34.
III. NONGYNECOLOGIC CYTOPATHOLOGY encompasses a wide variety of body sites, organs, and types of specimens. In general, any lesion that can be drained, brushed, washed, or scraped can be a “non-gyn” cytopathology specimen.
A. Specimen types
1. Fluid. These constitute a major category of non-gyn specimens and include pleural fluid, ascites/peritoneal fluid, pericardial fluid, and cerebrospinal fluid. Any loculated fluid can be drained and submitted for analysis (neck cyst, hepatic cyst, etc.) including synovial and vitreous fluid. Urine specimens, either voided or catheterized, are also commonly examined.
2. Brush. The endoscope makes it possible to introduce a brush and collect cells and tissue from a wide variety of internal locations. These include the bronchopulmonary tree (bronchial brush), alimentary tract (esophageal brush, gastric brush, and common/pancreatic/hepatic bile duct brushes), peritoneal cavity, and genitourinary tract (urethra brush, ureter brush, and renal pelvic brush).
3. Wash. Lesions sampled by a brush are usually accompanied by a “wash” specimen, which can be collected to sample additional cells. These specimens commonly include lung (bronchial wash, bronchoalveolar lavage), peritoneal cavity (pelvic wash), and urinary bladder (bladder wash, ureter wash, and renal pelvic wash).
4. Scrape. The Tzanck smear of the skin is utilized for the identification of mucocutaneous herpes virus effect.
B. Preparation and processing
1. Submission. Material can be submitted fresh or fixed. In general, unfixed material should be refrigerated until it can be delivered to the cytopathology lab. Even after arrival, it should be refrigerated until processed since unfixed cells in a fluid environment are in a constant state of degeneration, both in situ and after being collected. Specimens delayed in processing that have not properly handled can be uninterpretable.
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