Skin Disorders Guide

The use of a freezing temperature to cause cell death and tissue destruction (cryotherapy) has the same two advantages possessed by cauterants prior anesthesia by injection is not required, and bleeding does not occur.

Cryotherapy has two additional advantages.

• First, it is possible to freeze deep enough to treat malignant lesions(skin disorder).
• Second, the treated area remains sterile so long as the induced blister remains intact.

This relative freedom from posttherapeutic wound infection is particularly important when immuno suppressed patients have lesions that must be treated. On the other hand, cryotherapy shares with electro surgery and cauterants the disadvantages of prolonged healing time and the unavailability of tissue for histologic examination. Cryotherapy is easily used for benign lesions, but for the treatment of malignant lesions, thermocouple needles must be placed in order to be certain that the entire lesion has been adequately frozen.

Cryotherapy can be carried out in three ways. Most commonly, a cotton-tipped applicator is used to transfer liquid nitrogen (at a temperature of approximately -200°C) from a Thermos-type bottle to the lesion. Since the liquid nitrogen evaporates quickly, the cotton-tipped applicator must be redipped and reapplied multiple times to get an adequate freeze. The lesion blanches as it is frozen and this blanching must be maintained for at least 30 seconds. The depth of the freeze is regulated by the degree of pressure applied to the cotton-tipped applicator as well as by the length of time the lesion remains frozen. In most instances, however, to minimize the risk of scarring, the applicator is usually applied without pressure, the tip of the applicator simply rests on the lesion.

A second approach employs a canister from which the liquid nitrogen can be sprayed. A metal spray tip is affixed to an insulated metal bottle containing liquid nitrogen. Expansion of the liquid nitrogen forms sufficient pressure to expel the nitrogen in a narrow, fine spray. This spray is applied to the lesion for a total of 15 to 30 seconds. Sprayed liquid nitrogen can be applied quickly to multiple lesions, but it requires some skill to confine the freeze precisely and solely to the lesion. Several brands of commercial spray canisters are available.

Finally, liquid nitrogen can be circulated through a metal probe such that the tip of the probe approaches the temperature of the nitrogen itself. The machinery for this application is quite expensive and bulky, but this approach offers the highest possible degree of control over the size and depth of the tissue to be treated. Discomfort is only moderately great during the freeze, but it increases somewhat as the tissue thaws. For this reason it is not usually suitable for use in children below the age of 7 or 8 years.

A blister, often with hemorrhage, usually develops at the treated site the day after treatment. If the depth of the freeze was sufficient, the lesion that was treated will be lifted from the underlying dermis and will be sloughed along with the blister roof 7 to 14 days later. Post inflammatory hypo pigmentation sometimes occurs at the treated site, but actual scarring is rarely encountered.