Cervical high-grade squamous intraepithelial lesion on conventional cytology: Cytological patterns, pitfalls, and diagnostic clues

Background: Conventional cervical cytology, which has a relatively low sensitivity in diagnosing high-grade lesions as compared to liquid-based cytology, is still being practiced in low resource settings. This study aimed at elucidating various cytomorphological patterns, pitfalls, and subtle clues to high-grade squamous intraepithelial lesion (HSIL) diagnosis on conventional cervical cytology through cytologic-histologic correlation.

Methods: Cervical biopsies reported as CIN2/3 were correlated with their corresponding Pap smears over a 10-year period to determine the frequency of undercalls. For characterization of overcalls, cervical smears reported as HSIL and their corresponding biopsies during the same period were correlated. The discordant cases in both the groups were reviewed for problematic patterns and pitfalls in cytological diagnosis of HSIL.

Results: Of the 142 biopsies with CIN2/3, 29 (20.4%) cases had been undercalled on cytology. Sixteen (16) of these could be reclassified as ASC-H/HSIL on smear review. Smears showing predominant cells of low-grade squamous intraepithelial lesion grade with a few HSIL cells and those with small abnormal cells in an atrophic background formed the main confounders for HSIL underdiagnosis. Thirteen (13) out of 130 (10%) Pap smears called as HSIL, where biopsy diagnosis was less than CIN2, were labeled as overcalls. Atypical metaplasia, hyperchromatic crowded groups, and reparative changes constituted the major diagnostic pitfalls on cytology. A diligent smear review helped to reduce the undercall and overcall rates to 9.1% and 2.3%, respectively.

Conclusion: Awareness of morphological challenges in interpretation of HSIL among cytopathologists practicing cervical cytology would assist in reducing the diagnostic errors and ensure better patient management.