Treatment by cryotherapy – Principles
The technique of cryotherapy utilizes 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 discharged and 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 precancers (CIN 1, CIN 2 or CIN 3) on histopathology, if the cervix fulfils the criteria described earlier for ablative treatment. Cervical precancers suspected on colposcopy (‘colposcopy and treat’ approach) and fulfilling the criteria can be treated with cryotherapy without histopathologic 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 number of ‘over-treatment’ is expected with either colposcopy and treat or screen and treat approach as 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 clinics resulting in high compliance to treatment, which significantly outweigh the risk of over-treatment.