Laser treatment of vascular lesions

Published on 09/03/2015 by admin

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Last modified 09/03/2015

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2 Laser treatment of vascular lesions

Iris Kedar Rubin, Kristen M. Kelly

Summary and Key Features

• Vascular lesions are one of the most common indications for laser treatment

• Treatment of vascular lesions implements the theory of selective photothermolysis, confining thermal injury to the target of interest

• Pulsed dye laser remains the gold standard treatment for port-wine stains, and while most improve, the minority clear completely

• Early laser treatment improves port-wine stain response

• Alexandrite laser can be implemented for treatment of hypertrophic, or pulsed dye laser resistant, port-wine stains

• Indications for laser treatment of hemangiomas includes ulcerated lesions and involuted lesions with residual telangiectasias and / or textural change

• The role of laser treatment for proliferating hemangiomas remains less clear, and may be most beneficial for superficial hemangiomas

• Deeper-penetrating near-infrared lasers may be implemented to treat select venous malformations

• Vascular lasers and intense pulsed light are the treatment of choice for the background erythema and telangiectasias associated with rosacea

• Poikiloderma of Civatte can be successfully treated with intense pulsed light, or a combination of vascular and pigment selective lasers

Introduction and history

One of the first applications of lasers in dermatology was the removal of vascular lesions. Laser surgery has become the treatment of choice for many vascular lesions. The most common indications for treatment are vascular anomalies including port-wine stain birthmarks (PWS) and hemangiomas, as well as facial erythema and telangiectasias. Vascular specific lasers have seen an evolution from the historically used continuous wave lasers to pulsed lasers that implement the theory of selective photothermolysis, introduced by Anderson and Parrish in 1983.

In 1961, Dr Leon Goldman pioneered the use of lasers with a ruby device. Argon lasers were developed later in the 1960s and improved the color of PWS and hemangiomas, but resulted in unacceptably high rates of scarring and depigmentation due to non-specific heating of the superficial dermis. The theory of selective photothermolysis provided a mechanism to confine thermal injury to the target of interest and minimize collateral damage to surrounding tissue and allowed development of pulsed lasers.

Three components are necessary for selective photothermolysis: (1) a laser wavelength with preferential absorption of the target chromophore, (2) appropriate pulse duration matched to the target size, and (3) a fluence that both treats the target and minimizes non-specific thermal related injury. The ideal pulse duration is equal to or somewhat shorter than the thermal relaxation time of the target vessel. The thermal relaxation time is defined as the time for 50% of the heat to dissipate from the target of interest. A pulse duration that is too short may not be effective, whereas one that is too long may cause heat to dissipate to surrounding structures and cause unwanted thermal injury. The classic target chromophore for vascular lesions has been oxyhemoglobin, which has the greatest absorption peaks at 418, 542, and 577 nm (Fig. 2.1). The laser light is absorbed by oxyhemoglobin, and converted to heat, which is transferred to the vessel wall causing coagulation and vessel closure. Other hemoglobin species have more recently been recognized as appropriate targets, depending on the vascular lesion. For example, venous lesions may benefit from wavelengths of light that target deoxyhemoglobin. The alexandrite laser at 755 nm is close to a deoxyhemoglobin absorption peak and has been used for refractory or hypertrophic PWS, a venocapillary malformation. Methemoglobin absorption has also been recognized as a potential target chromophore.

Figure 2.1 Optical absorption of hemoglobin.

Source: Dr Scott Prahl, http://omlc.ogi.edu/spectra/hemoglobin.

Pulsed dye lasers (PDL) became available in 1986, and were initially developed at 577 nm to target the yellow absorption peak of oxyhemoglobin. It was later realized that, for selective photothermolysis to occur, the laser wavelength did not have to be at an absorption peak for the target chromophore as long as preferential absorption was still present. PDLs shifted to 585 nm, allowing for a depth of penetration of approximately 1.16 mm; 595 nm PDLs later became available to achieve greater depth of penetration. PDLs have also evolved to incorporate longer pulse durations. Early PDLs had a fixed pulse duration of 0.45 ms, whereas currently available PDLs have pulse durations from 0.45–40 ms. Longer pulse durations have the advantage of treating without purpura.

Epidermal cooling was introduced in the 1990s as a means to protect the epidermis, minimizing pigmentary changes and scarring. Cooling also permits the utilization of higher fluences and thus provides greater treatment efficacy. In addition, cooling minimizes discomfort associated with treatment. Modern cooling devices include dynamic spray, contact, and forced cold-air cooling.

Since the PDL penetrates to a depth of only 1–2 mm, other lasers have been developed to treat vascular lesions in an attempt to achieve a greater depth of penetration. The alexandrite laser at 755 nm and neodymium : yttrium aluminum garnet (Nd : YAG) laser at 1064 nm, for example, penetrate up to 50–75% deeper into the skin. Given that the absolute absorption of hemoglobin species is lower at these wavelengths, higher fluences are required.

Intense pulsed light (IPL) devices emit polychromatic non-coherent broadband light from 420 to 1400 nm with varying pulse durations. Filters are implemented to remove unwanted shorter wavelengths of light to treat vascular lesions with blue-green to yellow wavelengths.

The most commonly used vascular lasers and light sources include:

PDLs (585 nm, 595 nm)

potassium titanyl phosphate (KTP) (532 nm)

near-infrared long-pulsed lasers: alexandrite (755 nm), diode (800–810 nm, 940 nm), and Nd : YAG (1064 nm)

dual-wavelength lasers: Cynergy by Cynosure (pulsed dye at 595 nm and Nd : YAG at 1064 nm)

IPL sources with appropriate vascular-specific filters.

Vascular anomalies classification

The International Society for the Study of Vascular Anomalies (ISSVA) adopted a classification system in 1996 with two main categories. Vascular tumors are characterized by a proliferation of blood vessels, infantile hemangiomas being the most common. Vascular malformations are characterized by vessels with abnormal structure and normal endothelial cell turnover. Vascular malformations can be further subdivided into slow-flow lesions and fast-flow lesions. Capillary malformations, venous malformations, and lymphatic malformations are slow-flow lesions. Arterial malformations and arteriovenous malformations are fast-flow lesions. Complex-combined vascular malformations occur as well.

PWS, a type of capillary malformation, and hemangiomas are the two most common vascular anomalies that present for laser treatment (Table 2.1).

Table 2.1 Comparison of infantile hemangioma and port-wine stain

	Infantile hemangioma	Port-wine stain
Onset	First few weeks of life Precursor may be present at birth

Present at birth

Course

Proliferative period in first year of life, followed by slow involution

Does not regress

May become hypertrophic, more violaceous with age

May develop vascular blebs

Tissue marker

GLUT1 positive

GLUT1 negative

Port-wine stain birthmarks

Overview

PWS are vascular malformations that are composed of ectatic capillaries and post-capillary venules in the superficial vascular plexus. PWS vessels are characterized by diminished vascular tone and decreased density of nerves, especially those with autonomic function. In most cases, PWS are congenital, though in rare cases they may be acquired. PWS are found in approximately 0.3% of newborns. They tend to occur on the head and neck, although they may appear anywhere on the body. PWS persist throughout life and many thicken with time (Fig. 2.2). Geronemus et al reported that the mean age of hypertrophy is 37 years and, by the fifth decade, approximately 65% of lesions had become hypertrophied or nodular. There may be associated soft tissue overgrowth, leading to functional impairment in areas such as the lip or eyelid. Vascular blebs often form and may bleed with minimal trauma. These lesions are often considered disfiguring and many patients or their families seek treatment. PWS vessels vary in size from 7–300 µm with older patients tending to have larger vessels.

Figure 2.2 (A, B) Hypertrophic port-wine stain not yet treated.

PWS can be associated with various syndromes that are important to identify. A PWS in the V1 distribution raises the question of Sturge-Weber syndrome (SWS), which may have associated glaucoma, seizures, and developmental delay. Klippel-Trenaunay syndrome involves a PWS on an extremity, limb hypertrophy, and associated lymphatic / venous malformations. PWS can also occur in association with arteriovenous malformations in capillary malformation / arteriovenous malformation syndrome.

The goal of treatment of a PWS is to decrease or eliminate the red or sometimes violaceous color, improve appearance, and diminish psychosocial discomfort caused by these lesions. Treatment may also prevent development of blebs that may bleed or become infected. It has been theorized that treating PWS early may prevent hypertrophy as well. The PDL, which is strongly absorbed by oxyhemoglobin, is the most commonly used laser for treatment. Although PDL is effective and approximately 80% improve with treatment, only about 20% of PWS clear completely. Deeper-penetrating lasers have been used in an attempt to improve treatment outcomes. PWS response to laser treatment is variable. A study by Nguyen et al found predictors of improved response include small size (<20 cm²), location over bony areas, in particular the central forehead, and early treatment. A retrospective study by Chapas et al of 49 infants who started laser treatment by the age of 6 months demonstrated an impressive average clearance of 88.6% after 1 year, suggesting that early treatment may be advisable. Early treatment may be more beneficial due to thinner lesions and overall smaller lesions. Other factors must be considered in deciding when to initiate treatment, including anesthesia and the associated risks and benefits.

Huikeshoven et al have shown that PWS may redarken after laser therapy, though recurrent areas are still significantly lighter compared with baseline. This occurrence of redarkening may be due to revascularization that occurs as a response to injury and hypoxia and / or progressive dilatation of residual vessels as a result of decreased autonomic nerves.

The PDL is the most commonly used laser to treat PWS. Treatments are typically done at 4–6 week intervals, and it is not uncommon for 10 or more treatments to be performed initially until a plateau is reached or the lesion clears (Fig. 2.3). Larger spot sizes allow for greater depth of penetration and so the clinician should select the largest spot size that will provide sufficient fluence to achieve the desired end point, while confining the treatment to the area of interest. It is advisable to determine the fluence threshold on the darkest portion of the PWS with 1 or 2 test pulses before treating the entire lesion. The fluence is adjusted to achieve the desired end point. For the PDL, the desired end point is immediate purpura. A confluent gray color signifies that the fluence is too high. A cookbook approach to treatment may result in complications.