Histochemical evaluation of the coagulation depth after argon laser impact on a port‐wine stain

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Abstract
A two‐step excisional treatment of a port‐wine stain (PWS) on the back of a 43‐yr‐old female patient was performed. Immediately before the first surgical treatment, two corresponding series of argon laser impacts were performed, each on one PWS half. Different laser parameters with irradiances ranging from 95 to 382 W/cm2 and energy fluences ranging from 19 to 114,6 J/cm2 were used. Laser spots on the first part to be excised were biopsied 10 min after laser treatment and prepared for histochemical analysis by staining with nitro blue tetrazolium chloride (NBTC). Reduction of this redox dye by nicotinamide adenine dinucleotide diaphorase (NADH‐diaphorase) leads on frozen tissue sections to an intense blue precipitate. The activity of NADH‐diaphorase subsides immediately upon cell damage. All vital epidermal and dermal cells presented a dense blue granular pigment in their cytoplasm, sparing the nuclei. Laser induced arc‐shaped epidermal and dermal necrosis did not stain, showing a clear demarcation from surrounding vital tissue. The depth of the thermal injury ranged from 0.28 to 0.45 mm; it did not correlate with the chosen fluences. With these penetration depths, the vast majority of PWS vessels was affected. Assessment of the remaining part of the PWS 8 months later yielded blanching of all laser‐treated areas. With the NBTC method, an accurate definition of laser‐induced tissue damage is feasible. It could be shown that the exposure time is the most relevant parameter influencing the penetration depth.

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