To identify less readily identifiable patterns of high-grade squamous intraepithelial lesions (HSIL) in negative human papillomavirus (HPV)-positive Papanicolaou (Pap) tests on ThinPrep preparations.
Of all HPV-positive Pap tests that were negative for intraepithelial lesion or malignancy (NILM) from July 2013 to June 2018, those with HSIL on subsequent histology within 6 months were identified. ThinPrep slides from the latter group (group 1) and from NILM HPV-negative Pap tests with negative follow-up (group 2) were reviewed independently by 4 participants. Group 1 cases were then reviewed together for consensus and with the ThinPrep Imaging System (TIS). Any discrepancies from the original interpretation were recorded.
The study cohort included 57 cases each in groups 1 and 2. On final review of group 1 cases, 17 (29.8%) were classified as NILM or unsatisfactory. Of the remaining, 4 cases revealed rare abnormal cells not flagged by the TIS in the fields of view. In the 36 cases (63.1%) with screening or interpretative errors, the key cytologic findings accounting for major discrepancies included atypical metaplastic cells, atypical repair, rare syncytial groups, and atypical immature metaplastic cells.
There are 3 main underrecognized patterns of HSIL in cervical cytology: atypical metaplastic cells, atypical repair, and rare syncytial groups.

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