Comparative histochemistry of port-wine stains after copper vapor laser (578 nm) and argon laser treatment.

The present study compared the histologic changes occurring 15 min after copper vapor laser (CVL; operating at 578 nm) and argon laser (488/514 nm) treatment of port-wine stains (PWS) over a range of energy densities (8-32 J/cm2) with corresponding pulse widths of 50-200 ms. Frozen tissue sections were stained with nitroblue tetrazolium chloride (NBTC). This histochemical method permits an accurate color differentiation between blue-stained viable and unstained thermally damaged cells. At 8, 10, and 12 J/cm2 the argon-laser injury was confined to epidermal cell layers; none to superficial dermal effects were found. Fluences of at least 15 J/cm2 produced a diffuse NBTC-negative coagulation necrosis. Exposure of PWS skin to 8-12 J/cm2 at 578 nm did not alter the integrity of epidermal cells. In the dermis, damage was confined to blood vessels and surrounding collagen, showing a clear demarcation from adjacent viable structures. The maximum penetration depth achieved with these vessel selective energy densities was 0.44 mm. At 15 J/cm2, besides vascular injury, damage to the basal cell layer also occurred. At fluences of 17-20 J/cm2 a diffuse necrosis similar to that induced by the argon laser was found. Vessel selectivity of the 578 nm wave band was achieved with pulse widths from 50-74 ms, exceeding the estimated "ideal" exposure time (0.1-10.0 ms) for a vascular selective laser effect. The NBTC method allowed identification of subtle laser-induced tissue changes providing accurate quantitative data relating to the extent of vascular injury.