Proposed Sheffield quantitative criteria in cervical cytology to assist the diagnosis and grading of squamous intra-epithelial lesions, as some Bethesda system definitions require amendment.

OBJECTIVE: This study assesses the accuracy of published quantitative and qualitative criteria in the Bethesda System (TBS) for squamous intra-epithelial lesions. METHODS: Quantitative image analysis was undertaken on illustrations from TBS publications and also from slides in Cytology Training Centre teaching sets. Comparisons were also made with the British Society for Clinical Cytology (BSCC) terminology in cervical cytology, using the illustrations in their terminology publication and amalgamating the results into their proposed new two-tier model. RESULTS: TBS quantitatively defines low-grade squamous intra-epithelial lesions (LSIL) in both conventional and liquid-based cytology (LBC) preparations as showing nuclear enlargement more than x3 the area of a normal intermediate squamous cell nucleus. This study found that the increase in mean nuclear area was limited to only x2 in conventional preparations. In LBC (SurePath preparations, there was only a statistically non-significant x1.2 increase. This study identified a progressive and statistically significant reduction in mean cytoplasmic area from normal intermediate cells to LSIL and then to high-grade squamous intra-epithelial lesions (HSIL) in both conventional and LBC preparations. Furthermore, the most consistent quantitative finding in both conventional and LBC preparations was a statistically significant increase in the mean area and diameter ratios from normal intermediate cells to LSIL and then to HSIL. In all instances this varied from x2 to just below x3. This is in agreement with TBS, which states that the cytoplasmic area in HSIL is decreased leading to a marked increase in nuclear to cytoplasmic (NC) ratio. With the exception of an increase in mean nuclear area in conventional preparations from normal intermediate cells to LSIL, the predominant cause for this increase in NC ratios was a reduction in mean cytoplasmic area. The numerical increase in NC ratio for LSIL identified in this study was greater than implied by the 'slightly increased' statement in TBS. TBS comments that some HSIL cells can have the same degree of nuclear enlargement as in LSIL and that other HSIL cells may have much smaller nuclei than in LSIL. Both of these qualitative comments were supported in this study. The mean diameter NC ratios of 33% and 50% could provide useful diagnostic assistance in the distinction of normal intermediate cells and LSIL and between LSIL and HSIL, respectively. Because of overlapping individual ranges, however, additional diagnostic features such as nuclear morphology must be used in the distinction of normal intermediate cells, LSIL and HSIL. No statistical difference was identified in the mean diameter NC ratios between ASC-US and LSIL in TBS publications. In addition, the proposed new BSCC low and high grades of squamous abnormality were not statistically different from ASC-US/LSIL and HSIL, respectively. This provides support that the proposed BSCC two-tier system of squamous abnormalities is comparable to TBS. This study shows that LBC has variable but major and significant effects on nuclear and cytoplasmic morphology and that quantitative definitions in conventional preparations cannot be automatically extrapolated to LBC methodology. CONCLUSIONS: The study shows that some TBS quantitative and qualitative criteria require amendment and that an alternative quantitative approach, such as diameter NC ratio has a more valid scientific evidence base. Furthermore, use of NC ratios avoids the problems associated with the variable changes in nuclear and cytoplasmic areas, occurring between conventional and different commercial LBC preparations. By contrast, classifications based on area comparisons must be tailored to the specific conventional or commercial LBC preparation.

Proposed Sheffield quantitative criteria in cervical cytology to assist the grading of squamous cell dyskaryosis, as the British Society for Clinical Cytology definitions require amendment.

OBJECTIVE: In 1986, the British Society for Clinical Cytology (BSCC) published quantitative criteria to assist diagnosis in a three-tier grading system of squamous cell dyskaryosis. In dyskaryotic cells, area nuclear to cytoplasmic (NC) ratios below 50%, between 50% and 66% and over 66% were defined as equating with mild, moderate and severe grades respectively. Following the Terminology Conference in 2002, however, the BSCC recommended on their website that the three-tier model should be replaced by a new two-tier system of low- and high-grade squamous abnormalities. The latter broadly equate with the two-grade Bethesda System (TBS) for reporting squamous intraepithelial lesions. The purpose of this study was to assess the accuracy and reproducibility of the BSCC three-tier quantitative definitions, to investigate if they were applicable to liquid-based cytology (LBC) and to see how they related to the proposed new two-tier BSCC system. METHODS: Quantitative image analysis was undertaken on illustrations from the 1986 BSCC terminology publication and on microscope slides from external quality assessment and Cytology Training Centre teaching sets. RESULTS: Analysis of mean NC ratios showed that mild, moderate and severe dyskaryosis exist as statistically different populations. Overlap of NC ratio ranges, however, limits their practical application in the three-tier model, although interestingly no overlap was noted between mild and severe dyskaryosis. No grade of dyskaryosis had a mean area NC ratio over 50%, indicating that the BSCC quantitative definitions are incorrect. The mean diameter NC ratios for mild, moderate and severe dyskaryosis were found to be 40%, 49% and 66% respectively. Accordingly it is possible that those reporting cervical cytology could be interpreting the BSCC NC ratios as meaning diameter rather than area. Amalgamation of the three-tier results into the proposed two-tier model shows that the resulting mean NC area and diameter ratios identify statistically different low- and high-grade populations. The reduced degree of overlap, however, of NC ratio ranges in the two-tier model implies that NC ratios could have a useful practical role in the separation of the low- and high-grade categories. The two categories were reasonably well separated by mean area and diameter NC ratios of 25% and 50% respectively. A two-tier model combining mild with moderate rather than severe dyskaryosis was found to be a statistically valid alternative but gave rise to NC ratios that would be difficult to use in practice. Except for moderate dyskaryosis, no significant differences were identified between the mean NC ratios of either conventional and LBC preparations or LBC preparations using two different commercial methodologies (SurePath and ThinPrep). Differences, however, were noted in area measurements between SurePath and ThinPrep and this has potential implications for classifications (such as TBS) using area comparisons as their basis. In addition, it was found that the increased NC ratio, associated with higher grades of dyskaryosis is more a consequence of progressive cytoplasmic area reduction rather than nuclear area increase. The similar NC ratios of borderline nuclear changes associated with human papilloma virus and mild dyskaryosis support the BSCC proposal that these can be combined to constitute a low-grade category. This study shows that the BSCC area NC ratio criteria of grading squamous cell dyskaryosis require amendment. In addition, this study supports the new BSCC recommendation of low- and high-grade squamous cell categories. CONCLUSIONS: The study proposes Sheffield quantitative criteria to assist the grading of squamous cell abnormalities. Quantitative diameter NC ratio measurements, however, must always be accompanied by detailed assessment of qualitative morphological features and in particular those relating to nuclear chromatin. This is equally relevant to both two- and three-tier models.

External quality assessment in gynaecological cytology: The Trent Region experience. The Trent Regional Gynaecological Pathology Quality Assurance Group for the National Health Service Cervical Screening Programme.

A Department of Health Executive Letter stated in 1998 that the principal function of external quality assessment (EQA) is educational. Subsequently, in England, it has no longer been acceptable to assess performance in gynaecological cytology by proficiency testing. This paper describes the EQA scheme in gynaecological cytology that has been run by the Trent Regional Gynaecological Pathology Quality Assurance Group for the NHS Cervical Screening Programme (NHSCSP) since 1998. It conforms as closely as possible to the recommendations published by the Department of Health Working Group on Histopathology EQA Accreditation, and replaced the national proficiency testing protocol. The educational value of the scheme is derived predominantly from a numerical score which provides confidential and quantitative feedback to all participants. Personal performance monitoring occurs as a secondary function. For primary screeners and checkers, this is based purely on the distinction between negative, inadequate and abnormal smears. For pathologists, personal performance monitoring also includes grading of abnormalities. The EQA has been designed so that all professional groups participate in a manner that closely mimics normal practice. Only slides that have achieved an 80% consensus amongst participants are used in the EQA. Substandard performance has been defined as those participants with scores falling below the 2.5%ile. The paper describes the EQA in detail and illustrates its use by means of the second round results. The EQA protocol developed within Trent and described in this paper has contributed to proposals contained in the current national EQA in gynaecological cytology for the NHSCSP. In particular this paper highlights the effectiveness of the scoring system contained within the Trent and National EQA protocols.