الفهرس 
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Abstract
Laser surgery represents one of the most important advantages that have occurred in cutaneous surgery during the past century. Rapid developments in laser technology have made increasingly sophisticated systems available with a wide range of wavelengths, to treat different skin disorders. To most appropriately utilize any laser system, it is important to know how lasers are constructed and how they generate laser light. It is also vital to learn the basic laser physical principles and how the unique laser light properties interact with living tissue. An informed cutaneous surgeon will determine the proper clinical indications, benefits, limitations, and risks when employing each of the various laser systems. The advanced laser technology has greatly improved the ability to treat benign cutaneous melanocytic lesions. The wave length of QS-alexandrite (755nm) and the QS-ruby (694nm) fall within the peak absorption spectrum of melanin. Fortunately a therapeutic window of wave lengths exists between 630nm and 1100nm, where melanin absorption exceeds hemoglobin absorption. This makes both lasers an appropriate therapeutic option for a wide range of benign pigmented cutaneous lesions. The principles of selective photothermolysis are applied to the treatment of benign pigmented cutaneous lesions. Pulse durations less than 1us can effect selective photothermolysis of melanosomes. As the absorption of melanin falls with increasing wavelength, higher fluences were required at the longer wavelength of QS-alexandrite. Proper fluences induce damage through thermal effect and shock waves arising from rapid thermal induced expansion of tissues. Our clinical observations supports the following data. Targets have a three dimensional structure. Superficial components of the target will absorb light shadowing deeper targets. Multiple treatments are needed to get a complete clearance. The damage of pigmented lesions in darker skin tones suggests a selective effect at the level of melanosomes. A compromise between laser absorption in epidermal melanin (especially dark skin) and the laser specific depth penetration is needed. The clearing of pigmented lesions and the risk of adverse sequelae are related to the lesion anatomical site. Less favorable results were seen following treatment of trunk or leg lesions. This may be related to the thickness of epidermis and papillary dermis, the relative decrease in adnexal structures, and fewer blood vessels. Moreover an appropriate interval between sessions is mandatory to allow for adequate pigment remova Benign pigmented lesions represent a heterogenous group. Although melanin containing cells are destroyed, the clinical outcome is variable. This is due to the different underlying biology of such lesions. For benign epidermal lesions like freckles and lentigines, both systems can be considered as beneficial tool and suitable approach for the treatment. Nevus spilus lesions, with tan background and darker speckles, responded well to QS-red laser treatments. While the QS-alexandrite and the QS-ruby are equally suitable for treating lesions of nevus spilus, they may be not entirely useful for eradicating such lesions. Insufficient melanin in the involved melanocytes, and regenerating nevus cells explain the poor response. Laser therapy is an acceptable method of treating café au lait macules provided that the patients understand the possibility of recurrence. Repigmentation occurs from surrounding melanocytes. There is probably a cellular influence in the dermis that triggers the pigmentation in the more superficial cells. The QS-alexandrite is a better option due to less tissue splatter and pain during the treatment. Responding lesions of melasma to laser therapy often require ongoing intermittent therapy. The QS-alexandrite laser more efficiently targeted the lesion’s melanocytes without post treatment pigment or texture changes, compared to the QS-ruby. Similarly we proved that the QS-alexandrite provides better treatment response than the QS-ruby in postinflammatory hyperpigmentation lesions. The treatments were well tolerated with no texture changes. Furthermore we found that the QS-alexandrite is more convenient in treating Becker’s nevi even in dark skin tones, as the treatments were well tolerated with no pigment and texture alterations or recurrence after 3 months. Deep persisted pigment cells in adnexal structures account for recurring lesions. The QS-alexandrite was also more efficient in treating the dermal lesions of Ota in our study. The patients tolerated the treatments well with no tissue splatter. The patient who was treated by both lasers, found the ruby laser sessions more painful. Also the temporary pigment changes of the alexandrite group of patients lasted almost half the time of the ruby group. While treating nevomelanocytic nevi, the QS-alexandrite gave better clinical response than the QS-ruby, presumably because of its improved melanin absorption and the rapid treatment time. If the depth of nevomelanocytic nests could be accurately established, a reliable prediction of the laser treatment outcome could be made for nevomelanocytic nevi. The patients should be aware of the fact that multiple treatments are often necessary and recurrences are not uncommon. Combining long pulsed lasers and Q-switched systems will help in targeting deep dermal nevomelanocytic nests Although the QS-alexandrite laser proved to have a distinct clinical and pathological advantage in clearing epidermal and dermal benign pigmented lesions compared to the QS-ruby, it was recommended to confirm the obtained results in larger studies with more number of patients over long periods of follow up time.