The squamocolumnar junction, metaplastic change and the transformation zone
The squamo-columnar junction is located at the point where the squamous epithelium and the columnar epithelium meet. The location varies throughout a woman’s life due to the process of metaplastic changes in the cervical epithelium which occur after puberty and in pregnancy. The transformation zone is the name given to the area of the cervix comprised of epithelium which has undergone metaplastic change.
Definition of metaplasia
- 1: native squamous epithelium
- 2: columnar epithelium of endocervix
- 3: squamocolumnar junction (SCJ)
- 4: Eversion of endocervical epithelium
- 5: Metaplastic change in transformation zone
Clinical significance of squamous metaplasia in the cervix
In the cervix, the area of the epithelium that has undergone metaplastic change is called the transformation zone (TZ). Numerous studies have shown that the immature metaplastic epithelial cells are susceptible to carcinogens and most, if not all, cervical cancers arise here.
Other forms of metaplastic change in the cervix
This pattern of metaplastic change often occurs after surgical cone biopsy, diathermy loop biopsy or LLETZ biopsy. Histologically it is characterised by tuboendometrioid glands in the endocervix well away from the uterine isthmus. A key feature of tuboendometrioid change is that there is no associated endometrial stroma The metaplastic epithelium exhibit endometrial features including pseudostratification of the columnar cell nuclei, nuclear hyperchromasia, secretory apical snouting in addition to luminal ciliation.
In cervical smears , tuboendometrioid metaplastic changes may be misinterpreted as glandular neoplasia as the cells may form rather ragged crowded groups. However the absence of feathering and rosette formation and the uniform size and shape and the fine chromatin structure of the individual nuclei should permit the correct diagnosis. The presence of a ciliated cell border is diagnostic although a rare finding . ( see also Section on Pitfalls of Diagnosis in Module 10 .)
This pattern is characterised by the presence of goblet cells in the cervical epithelium and has been found in glandular neoplasms of the cervix.
Case 1 Tubal metaplasia of cervix Histology and cytology
Case 2 Tubal metaplasia of cervix Histology and cytology