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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

In the cervix, metaplastic change involves transformation of the endocervical epithelium to squamous epithelium.

Three histological stages have been identified:

Histological section to illustrate reserve cell hyperplasia in the glandular epithelium of the cervix. Note the proliferation of the reserve cells deep to the endocervical epithelium.
Histological section to illustrate immature squamous metaplastic epithelium in the cervix. Note the tendency of the reserve cells to stratify with a corresponding increase in the amount and density of the cytoplasm. The original columnar epithelium appears as a distinct layer on the surface of the immature metaplastic epithelium.
Histological section to illustrate mature squamous metaplastic epithelium in the cervix. The immature metaplastic epithelium has transformed into a fully mature metaplastic stratified squamous epithelium virtually indistinguishable from the original (native) squamous epithelium.
Illustrates metaplastic change from columnar to squamous epithelium in the uterine cervix. Note position of squamo columnar junction (arrow). Note the glandular epithelium deep to the metaplastic squamous epithelium.


Metaplastic change in the cervix and its physiological basis

Squamocolumnar junction prior to puberty.
Eversion of the endocervical epithelium at puberty and first pregnancy
Metaplastic change of endocervical epithelium in the transformation zone
Relocation of SCJ in the endocervical canal after the menopause



  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

Tuboendometriod metaplasia

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.)

Intestinal metaplasia

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 1 – Tubal metaplasia of cervix Histology and cytology
Case 2 – Tubal metaplasia of cervix Histology and cytology
Case 2 – Tubal metaplasia of cervix Histology and cytology