Fig. 17. A. Sign of human papilloma virus (HPV) infection: mild koilocytosis (koilocytes without nuclear atypia). This may be interpreted as atypical squamous cells of undetermined significance (ASCUS). (Papanicolaou, × 900). B. Koilocytes showing large defined perinuclear halos, binucleation, and slight nuclear atypia, with smudged chromatin. This would be classified as low-grade squamous intraepithelial lesions (LSIL). (Papanicolaou, × 800).