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We have noticed in our routine practice that there is some variation in the histological definition of the transformation zone of the uterine cervix. We decided to carry out an audit of other pathologists in the UK to see whether there is any variation.
Letters with five different possible definitions of the cervical transformation zone were sent out to members of the National Gynaecological External Quality Assessment scheme, asking them to tick the response they considered the most appropriate definition.
The five options in the questionnaire were:
Surface squamous epithelium in continuity with surface columnar epithelium (squamo–columnar junction) only.
Surface squamous epithelium with surface columnar epithelium or stromal gland/crypt, or both.
Surface squamous epithelium only.
Surface columnar epithelium only.
Surface columnar epithelium with squamous (metaplastic) epithelium in gland/crypt.
One hundred and seventeen questionnaires were sent out and responses were received from 82 histopathologists (70% response rate). Tables 1 and 2 summarise the results.
These results confirm our initial impression that there is confusion in the definition of the transformation zone.
The cervical transformation zone is a dynamic entity formed during puberty and, histologically, is the area where the glandular epithelium is being replaced by squamous epithelium.1 The junction between the two types of epithelium is the squamo–columnar junction.2,3 The transformation zone is not the same as the squamo–columnar junction but the squamo–columnar junction is part of the transformation zone.
The presence of squamous and columnar epithelium (be it on the surface or comprising a gland) will ideally represent the transformation zone histologically, but if a biopsy contains squamous epithelium only, it could still represent the transformation zone. If there is extensive squamous metaplasia in the transformation zone, histology cannot confirm sampling of the transformation zone because of the absence of glandular epithelium.
The fact that some of the respondents in this audit chose multiple options probably reflects the difficulty of defining this dynamic zone. We would cautiously recommend that the transformation zone should be defined by the presence of squamous and columnar epithelium in continuity and/or the presence of squamous epithelium with underlying glands.