Atlas of Colposcopy: Principles and Practice

The technique of cryotherapy depends on the destructive power of cold injury to the normal and neoplastic epithelial cells. 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, the tissue temperature is reduced to -20 °C, causing permanent damage to the epithelial cells.
The ectocervix has sparse sensory nerve endings. As a result, an ectocervical procedure like cryotherapy does not require any anaesthesia.

Cryotherapy should be used to treat only those CIN1/CIN2/CIN3 lesions that fulfil the following criteria:

• The lesion should be on the ectocervix without any extension to the endocervix or to the vagina.
• The SCJ should be at the external os or on the ectocervix (type 1 transformation zone).
• The lesion should not occupy more than 75% of the cervix.
• The size of the lesion should be such that it can be covered by the tip of the largest cryotherapy probe.
• There should not be any suspicion of invasive cancer on colposcopy or cytology.
• No glandular abnormality should be suspected on cytology.

A colposcopic examination before ablative treatment ensures that all the eligibility criteria are fulfilled.

Ideally, a punch biopsy should be obtained from the lesion before cryotherapy, although it is not necessary to wait for the biopsy report to perform the procedure. 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. However, this is likely to result in substantial over treatment and should be reserved for settings where colposcopy/histopathology facilities do not exist.