Atlas of Colposcopy: Principles and Practice

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Treatment by cryotherapy – Principles  

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.

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