Atypical squamous cells: update on current concepts

Although the term atypia has been used in the reporting of Papanicolaou test results since the inception of cervical cancer screening, the controversy regarding its use has been growing since the 1988 Bethesda System formalized its use as atypical squamous cells of undetermined significance (ASCUS). Subsequent Bethesda workshops defined morphologic criteria for ASCUS, and recommended qualifiers to guide physicians with management. This article summarizes the evolution of the terminology for reporting atypia on cervical cytology, its morphologic criteria, reporting differential diagnostic considerations, clinical significance, and related quality assurance guidelines.