Role of Reflectance Confocal Microscopy in Cryosurgery

Reflectance confocal microscopy (RCM) is a noninvasive in vivo imaging technique intended to help the clinician diagnostically view skin lesions in real time while avoiding trauma or scar formation from surgical biopsies. RCM’s principles rely on the natural variation of refractive indices in tissue structures at different depths of the skin. With the use of a near-infrared diode laser, light projected from the confocal microscope focuses on a specific point in the skin. Reflected light from this point is captured through a pinhole-sized opening by a detector. The use of such a small aperture segregates reflected light from the focal section of interest from other areas of tissue. The depth of light penetration is dependent on wavelength, laser power, reflectivity of the superficial layers of skin, and scattering properties of the dermis. Of all these factors, only laser power can be changed. At longer wavelengths, deeper penetration is gained at the expense of resolution; therefore, present single-laser confocal microscopes are fixed at 830 nm. Each section projects as a two-dimensional image with dimensions of 0.5 mm laterally and 4 mm axially that are oriented parallel (en face) to the skin surface. The resolution of each image is comparable to those of histological sections. A clinical breakthrough in RCM has been the capability to bring to the bedside an almost equivalent tool to histological evaluation without the need for invasive diagnostic procedures. In the setting of cryosurgery, RCM has the capability to aid in the diagnostic decision of a lesion prior to undergoing therapy, which has the advantage of avoiding postponing the treatment until the diagnosis is histologically confirmed. In addition, RCM allows monitoring the response of tumor to minimally invasive treatment, including cryotherapy. The sensitivity and specificity of RCM varies significantly across tumor types, level of training of the operator, and expertise of the individual interpreting the confocal images. This chapter will cover the applications of RCM.