Photothermally induced vessel-wall necrosis after pulsed dye laser treatment: lack of response in port-wine stains with small sized or deeply located vessels.

The optimal treatment of port-wine stains is laser-induced selective photothermolysis. Lesion color and location and the age of the patient are reported to influence the therapeutic outcome. This study was initiated to analyze the outcome not only by the clinical response of lightening, but also in terms of photothermally induced necrosis to the vessel wall. Punch biopsy specimens were taken from 51 patients before treatment. Post-treatment biopsies were taken after exposure to a pulsed dye laser (585-nm wavelength, 0.45-ms pulse length) with an irradiant fluence of 6.5 J/cm2. Vessel diameter, depth, and wall thickness were measured in all histologic slides. The viability of the vessel walls was evaluated using an enzyme histochemical method. Port-wine stains with good blanching had significantly more superficially located vessels than the moderate and poor responders (p < 0.000). The moderate and good responding lesions consisted of moderate-sized vessels with diameters of 38 +/- 17 micrometers and 38 +/- 19 micrometers (mean +/- SD), respectively. The lesions showing poor blanching had significantly smaller vessels, with a diameter of 19 +/- 6.5 micrometers < 0.000). Analyses of the post-treatment specimens showed that coagulated vessels were superficially located and of moderate size, whereas the viable vessels were small with a median diameter of 14 micrometers. The probability of coagulation correlated with the thickness of the vessel wall. These data indicate that the therapeutic outcome of port-wine stains can be improved by using the lesional vessel parameters to select the optimal laser wavelength, pulse duration, and dose.