Histology correlation with atypical squamous cells of undetermined significance (ASCUS) and low-grade squamous intraepithelial lesion (LSIL) cytology diagnoses: An argument to ensure ASCUS follow-up that is as aggressive as that for LSIL.

The purpose of the present study was to compare histology outcomes of cytological atypical squamous cells of undetermined significance (ASCUS) to the histology outcomes of cytological low-grade squamous intraepithelial lesion (LSIL). Cases with a cytology diagnosis of ASCUS and LSIL that had correlative histology obtained within 3 mo of the cervico-vaginal smear were accrued from the files of the Cytology and Histology Departments of Mercy Hospital Medical Center (Des Moines, IA). All of the cytology cases were examined by a cytotechnologist, a cytopathologist, and the histopathologist who signed out the biopsy material. The laboratory's benign: ASCUS: LSIL: HSIL + ratio was 94.0%: 3.8%: 1.5%: 0.7% for the time period of this analysis; its ASCUS:SIL proportion was 1.76. Histology correlations to 249 ASCUS cases showed 45 (18%) CIN2s (cervical intraepithelial neoplasm 2) or CIN3s, 134 (54%) CIN1s, and 70 (28%) nonneoplastic biopsies. Ten of 24 (42%) ASCUS cases that showed histological CIN3 and seven of 21 (33%) ASCUS cases that showed histological CIN2 contained atypical immature squamous metaplastic cells, while the remainder showed squamous cells with mature, superficial/intermediate-type cytoplasm. Histology correlations to 576 LSIL cases showed 96 (17%) CIN2s or CIN3s, 397 (69%) CIN1s, and 83 (14%) nonneoplastic biopsies. One hundred forty-six (59%) ASCUS and 424 (74%) LSILs had histological koilocytosis with nuclear atypia (KA); the sole histological finding of KA was seen among 76 (30.5%) ASCUS and 146 (25.3%) LSIL cases. The majority of cytological ASCUS and LSIL cases selected by clinicians for biopsy have histological CIN and a substantial minority show CIN2 and CIN3, which, in the case of ASCUS, is frequently associated with atypical immature squamous metaplastic cells. There is a high prevalence of histological KA among ASCUS and LSIL cases. Diagn. Cytopathol. 21:292-295, 1999. Copyright 1999 Wiley-Liss, Inc.