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4.1 Explain why chromatin pattern and distribution are considered to be the most important features defining the health status of epithelial cells.
Chromatin is a complex mix of DNA and proteins and is the ‘control centre’ for every cell in the body, ensuring that the processes essential for life are properly regulated. Cell division is, of course, one of these essential processes, and when cell division is disrupted as a result of neoplastic transformation then we can expected to see morphological changes in affected nuclei. These changes include coarsening and maldistribution of nuclear chromatin.
4.2 Discuss how the hormonal changes occurring during the menstrual cycle, pregnancy, and the menopause might affect the cytological appearances of a cervical sample. Describe some of the interpretive difficulties a cytologist might have in these circumstances.
Menstrual phase: endometrial cells, blood, and menstrual debris. Endometrial cells can mimic neoplastic cells, as will become evident in Chapter 5.
Proliferative phase: no specific hormonal pattern is recognized, but samples contain a gradually increasing proportion of superficial squamous cells, fewer intermediate cells, and less menstrual debris from day 4 to 14.
Ovulatory phase: the proportion of superficial squamous cells is at its maximum and menstrual debris is absent. This is the ideal time to take a cervical sample.
Secretory phase: samples contain a relatively high proportion of intermediate squamous cells, sometimes accompanied by numerous lactobacilli and cytolysis. The bare nuclei of cytolysed cells often show degenerative changes and can occasionally be mistaken for neoplastic cells.
Pregnancy: samples often contain a large number of glycogenated intermediate cells (navicular cells) due to high levels of circulating progesterone and oestrogen. These cells can mimic the effects of human papillomavirus infection.
Menopause: few superficial and intermediate squamous cells. Samples contain an increasing proportion of parabasal cells as the menopause proceeds. The relatively high N/C ratio of parabasal cells may lead to their misinterpretation as neoplastic cells.
4.3 Variation between cytologists in the visual interpretation of cells is a widely recognized problem in cytological practice. Can you suggest current and potential future approaches to minimizing such subjectivity? (Hint: refer to Chapters 6 and 17.)
Current approaches: robust initial and ongoing training programmes for all those involved in the microscopic interpretation of cell samples; internal and external quality control measures.
Future approaches: computer-assisted screening devices; adjunctive tests for molecular markers of neoplasia.
4.4 Historically, one of the factors that has limited the success of cervical screening programmes has been the high reporting rate of unsatisfactory samples. Discuss all the possible ways in which inadequacy rates can be kept to a minimum in a cervical screening programme.
High quality training programmes for those involved in taking cervical samples; use of liquid based processing techniques that maximize the efficiency of transferring cells from the sample to the slide (see Chapter 2); cytological criteria for the reliable recognition of adequate and inadequate cell samples.
4.5 Research suggests that the minimum acceptable cell count for a cervical sample might depend on the method of sampling and slide preparation. Discuss possible reasons for this finding.
The number and density of cells deposited on a glass slide during the processing of cervical cytology samples depends crucially on the selected preparation method, and is an important determinant of slide adequacy. For instance, cell sedimentation techniques differ fundamentally from membrane filtration methods, yielding slide preparations that are qualitatively and quantitatively different. Even subtle differences in processing technique (such as the manner in which cells are dislodged from the sampling device into the fixative medium) can affect the cell count in the final preparation.