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Atlas of visual inspection of the cervix with acetic acid for screening, triage, and assessment for treatment

Physiological changes of the cervical epithelium Ė Transformation zone of the cervix

  

The transformation zone (TZ) is the area of the cervix where the columnar epithelium has been replaced by or is being replaced by the metaplastic epithelium. It is bounded by the original SCJ at the outer (distal) limit and the new SCJ (simply called the SCJ) at the inner (proximal) limit. Although the SCJ as the proximal or inner boundary of the TZ can be very easily identified, the original SCJ is not so easy to recognize. The distal or outer limit of the TZ is identified by the location of the nabothian cyst or the crypt opening that is located farthest away from the external os.





If there is an acetowhite patch on the ectocervix that is connected to the SCJ, the farthest extent of the patch should be considered as the distal extent of the TZ.




The extent of the TZ varies with the womanís age. In a woman of reproductive age, the SCJ is usually fully visible and the TZ is located on the ectocervix. With advancing age, the cervix shrinks and the SCJ recedes into the endocervical canal. As a result, the TZ may be partially or completely inside the endocervical canal.





  • The extent of the TZ can be identified by the location of the crypt opening or the nabothian cyst that is farthest away from the external os. In the presence of an acetowhite patch arising from the SCJ, the distal limit of the patch coincides with the distal limit of the TZ, unless there are nabothian cysts or crypt openings located beyond that.
  • It is crucial to identify the TZ correctly, because all cervical precancers and cancers that originate from the squamous epithelium are initially located in the TZ.
  • Delineation of the limits of the TZ is also essential for treating a precancerous lesion on the cervix. The entire TZ must be ablated or excised, irrespective of the location of the abnormality.



Pregnancy may lead to certain physiological changes of the cervical epithelium.

































  


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