The treatment of vascular anomalies by selective laser photocoagulation has a history of more than 50 years. The treatment options have been continuously improved since then and have reached a high standard to this day. In the treatment of vascular anomalies, laser is firmly established alongside sclerotherapy/embolization, cryotherapy, surgical excision, and propanolol. This article goes into more detail about the various techniques and workings of the laser.
As early as 1963, Leon Goldman [1] made the first attempts to treat hemangiomas and nevi flammei with Ruby, Nd YAG and Argon lasers, which were published in 1968. R. Anderson and J. Parrish [2,3] first articulated the principles of selective photothermolysis of vessels in 1981 and 1983, respectively. Based on this, these treatment options have been continuously improved.
Numerically and economically, the therapy of pathological vascular lesions plays a minor role compared to the huge amount of cosmetic laser treatments. The revenues generated by this would probably allow an economically reasonable operation of a laser in the rarest of cases. Although social insurance companies, which are otherwise rightly very reluctant to cover laser treatments, do pay for therapies for the ethically recognized indications nevi flammei and hemangiomas. Overall, it is probably more the profits from cosmetic lasers that encourage the laser industry to continue investing in research and development in the field of cutaneous lasers.
The vascular anomalies, vascular tumors, and vascular malformations represent a heterogeneous entity. Extension and involvement of other organs require adequate workup. In complex situations, especially in hemangiomas in children, this is expediently organized by an interdisciplinary board [4] involving the pediatrician, dermatologist, plastic surgeon, interventional radiologist, and possibly the ORL specialist.
Depending on the situation, the therapy has to be interdisciplinary as well as the clarification. In addition to sclerotherapy/embolization, cryotherapy, surgical excision, propanolol, and possibly steroids or vincristine, laser has its significant place in the arsenal [5,6]. It cannot do everything, but in certain cases it may be the best therapeutic option.
Devices under consideration
The following range of laser devices has been in use for several years: KTP 532 nm, PDL 585 nm and 595 nm, Alexandrite 755 nm, Diode 810 nm, “long pulsed” Nd YAG laser 1064 nm and the IPL technique. The various devices differ not only in wavelength, but also in spot size, pulse lengths, pulse series, and cooling systems. Most laser applications are transcutaneous; less frequently, the approach is interstitial or endovenous. They all have the following common goal: emission of rays that reach a specific chromophore, hemoglobin, while sparing the environment as much as possible.
Laser tissue reaction
According to current knowledge, various events are likely to take place in the chromophore. Light absorption in hemoglobin causes heat damage especially to erythrocytes, resulting in “sludges” that stop blood flow for a period of time (hours, days, weeks). A stronger reaction is coagulation, which is associated with thrombus formation. The heat is transferred to the vessel wall, in which, in the minimal case, a vasospasm can occur due to shrinkage of the collagenous tissue. This often dissolves after minutes, which we can often observe during treatment. Ultimately, the goal of treatment is collapse of the vessel. The heat-induced endothelial damage should cause the vessel walls to stick together, and the vessel should remain occluded and resorbed [7].
What if the vessels do not close?
We know that with very fine pink vessels, e.g. on the nose, the absorption is low and the heat generated in the vessel is insufficient. This leads to the aforementioned transient spasm, but not to permanent obliteration.
By dealing with the light-tissue reaction we have knowledge about the following facts: For the specific heat damage of a vessel, besides wavelength and energy, the spot size and the pulse length play a role.
By controlling the latter parameter, we can cause the entire vessel cross-section to be heated and not just create partial vessel wall lesions. If we are dealing with thicker vessels, then we choose longer pulse times. Since these vessels are usually located somewhat deeper in the dermis, there is a further advantage for the longer wavelengths with the deeper penetration capacity into the tissue. Larger spots also allow deeper penetration. If we treat very fine vessels, then small spots, shorter wavelengths and shorter pulse times are sufficient.
IPL technology
The IPL devices cover a whole spectrum of wavelengths. This allows vessels of different sizes and depths to be reached. In addition, the energy output curve of certain IPL devices could be optimized. Pyramidal energy courses with long build-up/degradation phases as well as high peak values, which were associated with some risk of burns and vascular ruptures, can thus be avoided. This is achieved by rectangular energy discharges, the flat course of which tends to cause coagulation that penetrates the entire cross-section of the vessel.
Another special feature of the IPL technique deserves additional mention. As explained, the pulses can be shortened for the treatment of very fine vessels. However, it is important to note that if the energy remains the same and the pulse time is shorter, we will create a high-edged rectangle from a flat rectangle in the energy curve diagram. This increases the temperature of the xenon lamp and, according to Wien’s displacement law, changes the emission spectrum.
So, if we shorten the pulse time for the same energy flux, i.e. the same number of joules, we will have more shortwave radiation, which is well absorbed by bright red vessels. Conversely, with longer pulse duration, the infrared component is increased, which is better suited to treat deeper larger vessels [8,9].
Light-induced methemoglobin formation
We gain further improvements from the finding made years ago about light-induced methemoglobin formation. This is characterized by an absorption curve different from hemoglobin and oxy-hemoglobin, which is more in the range of longer wavelength light [10]. If a second light pulse is emitted, the newly formed chromophore can absorb it more, this means more heat, thus more intense photocoagulation. Double pulse technology is further optimized by individual manufacturers by combining two lasers of different wavelengths.
The very weak chromophore in the fine bright vessels is the reason why we do not achieve complete brightening there. The study group led by Professors W. Bäumler and M. Landthaler administers an exogenous chromophore before laser treatment to improve absorption. Indocyanine green is used, which has proven its worth in various fields of medical diagnostics since 1956. In the diagram, the absorption curve for isocyanine runs to the right of that for hemoglobin, i.e., in the longer wavelength region, and has a broad peak between 755 and 800 nm. Accordingly, the radiation of the diode laser is strongly absorbed at 810 nm [11].
The pigment as a troublemaker for successful photocoagulation
The short pulses and the short-wave rays, which are particularly useful parameters for light and fine vessels, are also very well absorbed by the pigments of the skin in competition with hemoglobin. This results in heating of the epidermis, which at a minimum manifests itself as transient erythema and at a maximum leads to ulceration, which heals under depigmented scar plates. Postinflammatory hyperpigmentation is also unpleasant. Cooling methods were developed very early on as the first countermeasures to counteract the unwanted heating of the epidermis. The simplest option is the use of cooling pads. Most units have a built-in cooling system, with cryospray or contact cooling. With the latter, care must be taken to press the contact piece very lightly, otherwise the vessel to be treated will be squeezed out and thus the chromophore will be pushed away.
Especially with IPL devices, finding the right parameters is of crucial importance – Wien’s distribution law should be recalled once again. A melanin meter is used to navigate between too much and too little light energy. It allows to avoid inadequate light pulses of too short duration or too high energy for a given degree of pigmentation of the epidermis and still find optimal parameters for the pulse. Another way to circumvent the unwanted light absorption by the epidermal pigment is to shoot fine channels through the epidermis with an Erbium: YAG laser. Laser pulses of other wavelengths can then be irradiated through these directly onto the desired target structures.
Laser in combination with rapamycin
Tuberous growth of once planned nevi flammei and recurrences after initially beautiful lightenings are unfortunately known facts. Recurrences are attributed to regeneration and revascularization of photocoagulated vessels induced by angiogenesis during normal wound healing. A study group from the Laser Beckman Institute at the University of Irvine CA has investigated the effect of the topical angiogenesis inhibitor rapamycin in an animal experiment. This showed that the formation of angiogenic growth factors stimulated by laser irradiation was suppressed, thus reducing the regeneration of photocoagulated vessels [12].
Wolfgang Thürlimann, MD
Literature:
- Solomon H, et al: Histopathology of the laser treatment of port-wine lesions. Biopsy studies of treated areas observed up to three years after laser impacts. J Invest Dermatol 1968 Feb; 50(2): 141-146.
- Anderson RR, Parrish JA: Microvasculature can be selectively damaged using dye lasers: a basic theory and experimental evidence in human skin. Lasers Surg Med 1981; 1(3): 263-276.
- Anderson RR, Parrish JA: Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science 1983 Apr 29; 220(4596): 524.
- Swiss Group for Vascular Anomalies in Children (SGVAC), Angiodysplasia Board at USZ Prof Beatrice Ammann-Vesti (Angiology, Clinic Director).
- Schöni M: Hemangiomas in childhood. Kristin Kernland Long Practice 2011; 100 (10): 55-584.
- Waldschmidt U, et al: The treatment of hemangiomas in childhood. Clinic and Polyclinic for Pediatric Surgery, Inselspital Bern PRAXIS Switzerland Med Forum 2007; 7: 613-620.
- Ross EV, et al: Pushing th Spectrum Optimizing Treatment of vascular and pigmented lesions. Expert Discussion 2010.
- Raulin C, et al.:Treatment of adult port-wine stains using intense pulsed light therapy ( PhotoDerm VL).Brief initial clinical report. Dermatol Surg 1997; 23: 594.
- Schröter CA, et al: Clinical significance of intense, pulsed light source on leg teleangiectasias up to 1 mm diameter. Eur J Dermatol 1997; 7: 38-42.
- Randeberg LL, et al: Methemoglobin Formation During Laser Induced Photothermolysis of Vascular Skin Lesions. Lasers Surg Med 2004; 34(5): 414-419.
- Klein A, et al: Indocyanine green-augmented diode laser treatment of port-wine stains: clinical and histological evidence for a new treatment option from a randomized controlled trial. Br J Dermatol 2012; 167: 333-342.
- Jia W, et al: Long-Term Blood Vessel Removal With Combined Laser and Topical Rapamycin Antiangiogenic Therapy: Implications for Effective Port Wine Stain Treatment. Lasers Surg Med 2010 February; 42(2): 105-112.
CONCLUSION FOR PRACTICE
- Laser is firmly established alongside sclerotherapy/embolization, cryotherapy, surgical excision, and propanolol in the treatment of vascular anomalies.
- The following range of laser devices is used: KTP 532 nm, PDL 585 nm and 595 nm, Alexandrite 755 nm, Diode 810 nm, “long pulsed” Nd YAG laser 1064 nm and the IPL technique.
- The aim is to emit beams that reach a specific chromophore, hemoglobin, while sparing the environment as much as possible. Ultimately, the treatment should cause the vessel to collapse.
- In addition to wavelength and energy, the spot size and pulse length are decisive for the specific heat damage to a vessel.
- The pigment is the troublemaker of successful photocoagulation.
DERMATOLOGIE PRAXIS 2014; 24(2): 22-25
