In the 1950s, some cytologists began to promote a more scientifically accurate terminology that would allow cytological diagnoses to translate directly into histological diagnoses. This terminology (Table 15) was later adopted by the World Health Organization (WHO) (Riotton et al., 1973). The WHO terminology allows more precise correlation between cytological and histopathological findings, but is difficult to use since it includes a number of different entities.
These are mild dysplasia, moderate dysplasia, severe dysplasia, epidermoid carcinoma in situ, epidermoid carcinoma in situ with minimal stromal invasion, invasive epidermoid microcarcinoma and invasive epidermoid carcinoma. Studies have shown high rates of intra-observer and inter observer variation with cervical cytology in general (Yobs et al., 1987; Klinkhamer et al., 1988; Selvaggi, 1999; Stoler & Schiffman, 2001).
Classification systems that utilize more diagnostic categories have inherently higher rates of variability than do classification systems with fewer diagnostic categories (Yobs et al., 1987; Selvaggi, 1999; Stoler & Schiffman, 2001; Kundel & Polansky, 2003). Other limitations of the WHO terminology are that it does not adequately deal with non-neoplastic conditions nor with specimen adequacy. Despite its limitations, many cytologists around the world continue to utilize the WHO terminology.