Treatment by cryotherapy – Principles
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The technique of cryotherapy uses the destructive power of cold injury on the normal and neoplastic epithelial cells of the transformation zone. Nitrous oxide (N2O) or carbon dioxide (CO2) gases are used to induce the freezing effect on the cervix. The temperature of either of the gases, when released to atmospheric pressure from a compressed state, drops to –60 to –80 °C. When the gas is applied to the cervix through a probe, the tissue temperature is reduced to –20 °C, causing permanent damage to the epithelial cells. The destroyed cells are shed and are gradually replaced by healthy epithelium within a few weeks. The cold injury also damages cervical tissue up to a depth of 7 mm from the surface. As a result, any CIN extending to the crypts (usually the maximum length of a crypt is 5 mm) is adequately treated with cryotherapy.
The ectocervix has sparse sensory nerve endings. As a result, an ectocervical procedure like cryotherapy does not require any anaesthesia.
Cryotherapy may be used to treat any grade of cervical precancer (CIN1, CIN2, or CIN3) on histopathology, if the cervix fulfils the criteria described earlier for ablative treatment. Cervical precancers suspected on colposcopy (in the colposcopy-and-treat approach) and fulfilling the criteria can be treated with cryotherapy without histopathological verification. In the screen-and-treat approach, cryotherapy can be performed for VIA- or HPV-positive women who fulfil the above-mentioned criteria without colposcopic or histopathological verification. A significant rate of overtreatment is expected with either a colposcopy-and-treat or a screen-and-treat approach, because many of the women with colposcopically suspected CIN or positive VIA or HPV test results may not have any CIN. Nonetheless, the major advantage of such approaches is that the women require fewer visits to the clinic, resulting in high compliance with treatment, which significantly outweighs the risk of overtreatment.