Atlas of Colposcopy: Principles and Practice

The congenital transformation zone (CTZ) is an abnormal development of the squamous epithelium characterized by excessive maturation of the superficial layers and incomplete maturation of the deeper layers. This is a deviation from the normal metaplastic process in utero and does not have any neoplastic potential. The condition is seen in 3–5% of young women undergoing colposcopy. No treatment is required, and the changes disappear with age. However, it causes a diagnostic dilemma for the colposcopist.
The CTZ appears as a large oblong (lozenge-shaped) thin acetowhite area on the cervix. The lesion often extends from the anterior to the posterior fornix of the vagina.

The characteristic feature of the CTZ is a fine mosaic pattern on the surface. The margin of the acetowhite area is sharp but often irregular.

The CTZ shows patchy iodine uptake after application of Lugol’s iodine. The extension of the lesion to the vagina and the characteristic oblong shape become obvious after application of Lugol’s iodine and help to clinch the diagnosis.

Note: The CTZ does not require any treatment. However, at times it is very difficult to differentiate the CTZ from cervical premalignant lesions. In such cases, multiple biopsies are recommended.