Treatment of port-wine stains: analysis

Port-wine stains (PWS) are bluish red skin stains that are caused by enlarged, ectatic blood vessels in the dermis. Laser treatment of PWS is analyzed from computation of the spatial distribution of heat production by direct absorption of the laser light and subsequent heat conduction. The absorption and scattering caused by oxyhemoglobin, epidermis, and dermis as a function of wavelength are utilized in this analysis. Ideal treatment is defined as coagulating the ectatic blood vessels without irreversible damage to the epidermis and dermis. The analysis shows that a millisecond pulsed, yellow dye laser at 577 nm (one of the large absorption bands in blood) is the laser of choice to treat PWS, offering as close to the "ideal treatment" as possible. The blue-green argon laser, which is currently the most frequently used laser for this purpose, is strongly recommended with irradiation times in milliseconds. Other lasers that are in clinical use, such as the red ruby and near-infrared Nd-YAG lasers, can provide selective treatment only when the epidermis is cooled concurrently. The CO2 laser, on the other hand, can coagulate the blood vessels only through heat conduction from the hot epidermis; hence, it has neither the treatment selectivity nor any other physical option to force this selectivity.