This technique, as used by dermatologists, usually employs a high-frequency monopolar or spark-gap type apparatus, rather than a bipolar unit such as the Bovie machine. Monopolar electrosurgical apparatus requires no patient ground. There are two types of electrosurgery, electrofulguration and electrodesiccation. In the former, the tip of the electrode needle is held a short distance above the skin, and the area to be treated is ‘sprayed’ with the spark which jumps the gap from the electrode tip to the lesion surface. This method produces very superficial tissue necrosis and is thus suitable only for very superficial lesions. Electrodesiccation, the second technique, requires the tip of the electrode to rest in contact with the lesion surface. This produces a hemispherical zone of necrosis which is deeper than that achieved with electrofulguration. Both techniques require removal of charred tissue with a curette or scalpel as treatment proceeds. Simple electrodesiccation and curettage is frequently employed in the treatment of warts, seborrhoeic keratoses, and other small benign skin lesions. Malignant lesions, particularly basal cell carcinoma, may also be treated by this technique, although it is associated with a relatively high risk of recurrence.

All electrosurgical procedures should be performed after induction of adequate local anaesthesia. Electrosurgery should be used with caution or not at all in patients with cardiac pacemakers: the radiofrequency output of these units may be sensed by older pacemakers, although this is seldom a problem, and most modern pacemakers are not inactivated by the electrosurgical apparatus. Electrical equipment should not be used in proximity to alcoholic solutions or to dry gauze because of enhanced flammability.

Extreme cold causes cell death as a result of intracellular ice crystal formation and electrolyte concentration. Cryosurgery may be employed in the treatment of benign lesions such as actinic keratoses and warts, and is also frequently used in the treatment of basal cell carcinoma and squamous cell carcinoma. Liquid nitrogen is the most commonly used cryorefrigerant; it may be applied with a cotton tipped applicator, a spray apparatus, or a recirculating closed probe system.

Regardless of the technique used, benign lesions such as warts or actinic keratoses are treated for 10 to 20 s. Basal cell and squamous cell carcinoma require longer treatment times, typically two or more freeze cycles of 30 to 45 s each. Only the spray or cryoprobe units should be used for treatment of skin cancers, since the depth of ice formation with the cotton-tipped applicator method is insufficient to ensure necrosis of the full thickness of an invasive tumour.

The principal advantage of cryosurgery over other treatments of benign lesions is the speed with which multiple lesions may be treated. Anaesthesia is not generally required for treatment of small, superficial lesions, although larger tumours should be treated under local anaesthetic.

Treatment is followed by oedema, erythema, and blister formation. Healing takes place by secondary intention; in the case of large skin cancers this may require several weeks. Treatment of superficial lesions leaves little or no scarring, but unsightly hypopigmented scars invariably result from treatment of skin cancers. For this reason, cryosurgery is not an appropriate treatment for cutaneous malignancies when the cosmetic outcome is important.

Like electrodesiccation and curettage, cryosurgical destruction of cutaneous malignancies carries some risk of recurrence. Basal cell carcinomas occurring in the so-called ‘high risk’ areas should not be treated with this modality: when possible, surgical excision or Mohs' micrographic surgical excision should be used.

This is a surgical technique whereby the radial and vertical extent of tumour growth can be mapped intraoperatively, allowing very precise extirpation of even very small foci of carcinoma. Unlike conventional vertical sections, the histological sections used in the Mohs' technique are cut parallel to the cutaneous surface and tangentially through the epidermis, allowing simultaneous visualization of the entire deep and lateral margin of the excision specimen. Excision of the tumour proceeds in stages; after initial debulking of the visible tumour, additional horizontal sections may be excised sequentially. Each section is examined for the presence of residual tumour at the deep or lateral margin, and subsequent sections are taken of any residual foci. The procedure is completed when no residual tumour can be found at any margin.

Originally, zinc chloride paste was used to fix the tumour in situ. The tumour was then excised, but deeper sections could not be taken until the wound had again been fixed with zinc chloride. Such treatment was painful and took many days to remove most tumours completely. In 1974, Tromovitch and Stegman described the fresh tissue technique, which employs frozen histological sections rather than in-situ fixation with zinc chloride. This technique is now universally employed for the treatment of recurrent carcinomas, aggressive basal cell carcinomas, and carcinomas arising in areas at high risk of recurrence.

After successful removal of the tumour, conventional reconstructive surgical procedures are usually employed to repair the resultant defect. Large or complex defects are frequently treated by the combined efforts of the dermatological surgeon, plastic surgeon, otolaryngologist, or neurosurgeon as appropriate.

A number of lasers are used in dermatology. In general terms, a laser consists of an optical resonator, a power source, and an optical mechanism to direct the beam towards the target. Lasers are commonly named according to the nature of the substance within the optical resonator which, when energized, produces light. The beam produced by a laser is a unique type of electromagnetic radiation which is monochromatic, coherent (i.e., all light waves are in phase), and highly collimated.

Carbon dioxide lasers are commonly employed in dermatological surgery as well as in gynaecological and general surgery. The light produced by these devices is emitted in the far infrared portion of the spectrum, with a wave length of 10600 nm. Infrared radiation is absorbed by water, and any cell type may be ablated with this laser: the carbon dioxide laser is therefore not selective, but rather works by vaporization of any tissue in its path. This type of laser is particularly useful for removal of warts, syringomas, epidermal naevi, and other superficial lesions. Healing takes place by secondary intention. The carbon dioxide laser may be used in a defocused mode to remove excess tissue with a sculpting or ‘airbrush’ technique, as is often employed in the treatment of rhinophyma. This laser invariably causes some degree of scarring, and, for that reason, its use in the treatment of portwine stains and tattoos has largely become obsolete.

Argon lasers emit light at 488 and 514 nm, in the blue-green region of the visible spectrum. These wavelengths are absorbed primarily by haemoglobin and melanin, which results in thermal destruction of cutaneous structures containing those pigments. Unlike tuneable dye lasers (see below), the argon laser produces a continuous output, rather than brief pulses of energy, resulting in widespread damage to dermal and epidermal structures surrounding the pigment-containing portions of the skin. As a result, treatment of lesions with the argon laser generally results in some degree of scarring; this is usually less severe than that produced by the carbon dioxide laser. Argon lasers have been used to treat a variety of vascular lesions of the skin such as portwine stains, haemangiomas, telangiectasias, and venous lakes, but have now largely been replaced by the less destructive tuneable dye lasers.

Tuneable dye lasers employ an organic dye as the lasing medium. The dye is stimulated to emit photons by ‘pumping’ it with an argon laser beam or a flashlamp. The output wavelength of dye lasers may be adjusted, or tuned, to match the absorption spectrum of target chromophores. Tuneable dye lasers used in dermatology produce wavelengths of 577 nm or 585 nm, both of which fall in the yellow part of the visible spectrum. These wavelengths correspond to light absorption peaks of oxyhaemoglobin, and are thus relatively selective for structures which contain red blood cells. Melanin also absorbs small amounts of light at these wavelengths, and melanin-containing structures may be damaged during treatment with tuneable dye lasers.

The most important difference between tuneable dye lasers and the argon laser is the short pulse duration of the dye laser, which prevents thermal damage at distances greater than a few microns from the target blood vessels in the skin. As a result, non-specific thermal damage to the dermis is minimized, and scarring is greatly reduced. It is now possible to treat portwine stains and other superficial vascular malformations of the skin with the pulsed tuneable dye lasers without scarring of the skin.

Ruby lasers were developed in the 1950s and until recently have had few legitimate medical applications. By coupling a ruby laser, which emits red light (694 nm) with an electronic mechanism know as a Q-switch, which compresses the output of the laser into extremely brief pulses of extremely high energy, it is possible to destroy pigment granules in tattoos. In early trials, the Q-switched ruby laser produced clearing of up to 80 per cent of amateur tattoos and approximately 30 per cent of professionally applied tattoos. Tattoos composed of black carbon pigment (such as post-traumatic tattoos) respond particularly well; red areas in coloured tattoos do not absorb the red laser light, and do not respond to this treatment. Most tattoos can be removed partially or completely without appreciable cutaneous scarring. Hypopigmentation occurs in most patients, but resolves spontaneously after 6 to 24 months.

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Mohs FE. Chemosurgery. A microscopically controlled method of cancer excision. Arch Surg 1941; 42: 279–95.

Taylor CR, et al. Treatment of tattoos by Q-switched ruby laser. Arch Dermatol 1990; 126: 893–9.

Tromovitch TA, Stegman SJ. Microscopically controlled excision of skin tumors. Chemosurgery (Mohs): fresh tissue technique. Arch Dermatol 1974; 110: 231.

Zacarian SA. Complications, indications, and contraindications in cryosurgery. In: Zacarian SA, ed. Cryosurgery for Skin Cancer and Cutaneous Disorders. St Louis: CV Mosby Co, 1985; 283.