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

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

Filter by language: English / FranÁais / EspaŮol / Русский / українська

VIA procedure Ė Examination after application of 5% acetic acid Ė Normal features Ė Transformation zone (TZ)


The transformation zone (TZ) is the area on the cervix where metaplastic changes take place. The TZ can be identified by the presence of the metaplastic epithelium, nabothian cysts, crypt openings, and islands of columnar epithelium. In the fully mature squamous epithelium, none of the features of metaplasia may be visible. In the presence of a CIN lesion, extent of TZ is determined by the extent of the lesion. The TZ may be completely or partially inside the endocervical canal, if the SCJ moves inside the canal. This is frequently seen in postmenopausal women.

How to identify the extent of the TZ:

  • The proximal or inner limit of the TZ is the SCJ (the new SCJ).
  • The distal or outer limit of the TZ (the original SCJ) is identified by locating the nabothian cyst or the crypt opening that is farthest away from the SCJ on the ectocervix.
  • Once the farthest crypt opening or nabothian cyst is identified, the distal limit of the TZ can be delineated by drawing an imaginary circle with the farthest crypt opening or nabothian cyst on it.
  • In mature squamous epithelium, the above-mentioned features may be absent. In such situations, the distal limit of the TZ (the original SCJ) cannot be demarcated.
  • If there is a CIN lesion, the entire lesion should be considered as incorporated in the TZ.
The TZ is classified as type 1, type 2, or type 3, depending on its extension to the endocervix and the visibility of the SCJ. The details are described in later sections describing treatment.

Squamous metaplastic epithelium appears pale pinkish and is present towards the external os. It is often visible as tongue-shaped projections of pinkish epithelium projecting and coalescing towards the external os. Sometimes the metaplastic epithelium may be faintly acetowhite without any distinct outside border.

Metaplastic epithelium may also appear as a thin transparent acetowhite patch extending outwards from the external os with a diffuse or feathery margin.

Nabothian cysts are a feature of the TZ. A nabothian cyst looks like a raised pearly white or ivory white pimple on the squamous epithelium, and it becomes prominent after application of acetic acid.

Crypt openings (usually visible with magnification) are present only in the TZ. After application of acetic acid, the tiny crypt opening appears as a small black dot surrounded by a thin acetowhite rim. During VIA, crypt openings may look like small white spots on the squamous epithelium.

A skip area or an island of columnar epithelium is visible as a small pocket of red columnar epithelium on the metaplastic squamous epithelium. The process of replacement of columnar epithelium by metaplastic epithelium is not always uniform, and small islands of red columnar epithelium may be left behind on the original ectropion.


Click on the pictures to magnify and display the legends
IARC, 150 Cours Albert Thomas, 69372 Lyon CEDEX 08, France - Tel: +33 (0)4 72 73 84 85 - Fax: +33 (0)4 72 73 85 75
© IARC 2024 - All Rights Reserved.