Richard Castillo, OD, DO, FASOS, began his 2-part presentation on cryosurgery at SECO by distinguishing it from cryobiology (the study of low temperatures on living tissue) and cryotherapy (controlled cold exposure above freezing to induce physiologic change without tissue destruction). Cryosurgical tissue destruction occurs through several mechanisms, including intracellular and extracellular ice formation, solution effects, cold protein denaturation, and vascular and inflammatory reactions, he said. Cell death may result from necrosis, necroptosis, apoptosis, and vascular damage.

Dr. Castillo noted that ice formation is the most efficient killing mechanism. It is achieved through rapid cooling rates and homogeneous nucleation (crystallization), using a cryogen: liquid nitrogen at -320°F. The width, depth, and circumscription of cryogenic effect are influenced by 4 primary parameters:

1. Cooling rate of tissue,
2. Tissue end temperature,
3. Freeze hold time, and
4. Thawing rate.

The freezing front advances both horizontally across the skin and vertically through skin depth following an isotherm pattern. Isotherms represent temperature zones of equal temperature where the center of the treated area is the coldest and the periphery is warmer. In open spray application, liquid nitrogen forms a conical pattern. The instantaneous diameter of the frozen zone depends primarily on tip diameter and distance to the skin. The cone height corresponds to the distance between the tip opening and the skin, and the radius extends from the freezing center to the halo zone periphery. Because air is a poor conductor, increased distance reduces freezing effectiveness. The spray angle changes with greater distances, so consistent distance should be maintained. Nozzle inclination also affects freeze geometry. When held parallel to the skin, the cone is spherical. If tilted, freezing becomes oblique and irregular and produces greater destruction on the side closer to the skin.

Tip diameter directly affects the amount of liquid nitrogen released. Small apertures are recommended for delicate, superficial freezing of well-defined lesions of the eyelid. Dr. Castillo further described 4 cryotechniques:

1. Surface Freeze: Pendular “paintbrush” movements should be used for superficial freezing. For elevated lesions that require depth, surgeons can maintain a stable central freeze which then expands peripherally. This is referred to as the timed spot freeze.
2. Semi-Open Technique: This technique constrains the spray to a defined area using rubber cones, polycarbonate plates, or otoscope specula. It is always used around the eye to protect the globe and ocular surface. Metal cones are contraindicated because they conduct cold and may adhere to tissue.
3. Closed Probe Technique: Probes provide more control in the eyelid and periorbital regions and are preferred for vascular lesions, because applied pressure displaces blood prior to destruction. Smaller probes allow visualization of the expanding freezing front.
4. Cryotweezers Technique: Teflon-coated cryotweezers are used for skin tags, papillomas, and small pedunculated eyelid lesions. First, decant liquid nitrogen into a styrofoam cup and immerse the tweezer head until boiling stops (~30 seconds). Then remove the tweezer head from the cup and wait an additional 30 seconds until the head turns white. Grasp, extend, and hold the lesion for 5 to 10 seconds until the frost extends to the lesion base, and then release to allow thawing. No injection anesthesia is required for cryotweezer procedures.
   

   Billing and Coding

   • Skin tags: 11200 or 11201
   • Benign lesions (ie, warts, seborrheic keratoses): 17110 for less than 14 lesions and 17111 for more than 15 lesions
   • First premalignant lesions (ie, actinic keratoses): 17000
   • Second through 14th premalignant lesions: 17003 (per lesion)
   • 15th or more premalignant lesions: 17004 (for all lesions)
   • Eyelid margin lesions: 67850 (per lesion)

   Lesion size does not affect coding in the destruction of skin tags, benign, or premalignant lesions. Location matters for benign lesions, but not for skin tags or actinic keratoses.

   It is fast and comfortable for patients and carries a low risk of hyperpigmentation or hypopigmentation. Patients can also have multiple lesions treated in 1 session with the tweezer technique.

Common, temporary complications that occur early posttreatment include pain during freeze and thaw, blistering, bruising, and edema. Uncommon complications to watch for early after treatment are forehead headache and syncope. Infection, bleeding, pyogenic granuloma, delayed healing, and hypopigmentation are less common, delayed reactions, and hypopigmentation may be permanent. Other permanent complications include milia, atrophic or hypertrophic scarring, neuropathic pain, ectropion, eyelid notch, or lash loss.

“Always use semi-open techniques with protective cones, plates, and/or nonconductive (plastic) corneal shields to protect the surface of the eye when using spray techniques,” Dr. Castillo said. He added, “there is no excuse for failing to protect the globe.” OM