Why is high grade squamous intraepithelial neoplasia under-diagnosed on cytology in a quarter of cases? Analysis of smear characteristics in discrepant cases

BACKGROUND: The accuracy of cervical cytology has been quwstioned due to high false negative rate. In order to improve the sensitivity of cytology it is prudent to analyze the factors which hamper with the diagnosis of high grade lesions. AIMS: To study the cyto-histologic agreement in High grade squamous intraepithelial lesions (HSIL) of uterine cervix and to analyze the smear characteristics in discrepant cases. SETTINGS AND DESIGN: Cervical smears of 100 histology proven cases of Cervical intraepithelial neoplasia III ( CIN III ) were retrieved and reviewed to study cyto-histologic agreement in the diagnosis of high grade lesions.. The discrepant smears, undercalled on cytology, were further analyzed to determine the reasons for misinterpretations. Statistical analysis was performed to find out any significant factors for discrepancies. RESULTS: Cytology was able to correctly identify 74 HSILs while in 26 cases a diagnosis of Low grade squamous intraepithelial lesions (LSIL) or below was given. On review, 16 of these non correlating cases could be reclassified as HSIL on cytology while in 10 the diagnosis of LSIL or less persisted. 12/16 (75%) discrepant cases, reclassified as HSIL represented interpretive errors. Sampling errors (7/ 10) and air drying (5/10) were more frequent in under diagnosed cases. The statistical analysis did not yield any significant differences in the two review groups. CONCLUSION: 26% of HSIL cases were underdiagnosed on cervical smears. The major confounding factors responsible for under interpretation on cytology included air drying artifacts and metaplastic maturation of abnormal cells.