Vascular lesions can be
treated with laser techniques
called continuous wave
(CW) and Pulsed Delivery
Lasers (PDL). The chromophore
targeted is oxyhemoglobin,
although melanin absorption
also takes place, mainly
at shorter wave lengths.
Penetration is approximately
1mm and is greatest at
the longest wave lengths.
Pulsed laser (PDL)
Pulsed laser was initially
developed for specifically
treating vascular lesions
and is now preferred since
the pulsed delivery limits
thermal damage. Also, due
to low melanin absorption,
irregular pigmentation
is less. Earlier, the pulse
duration was shorter and
considerably less than
the thermal relaxation
time of superficial blood
vessels, causing less thermal
damage to untargeted tissues.
In the newer system, the
pulse duration is more,
allowing treatment of large
diameter blood vessels,
and the wave length is
longer, allowing greater
penetration. The new systems
operate at wave lengths
between 585nm and 600nm.
Currently PDL is the standard
treatment for childhood
vascular lesions, especially
port wine stains. In port
wine stain treatment there
is minimum microvascular
and vascular damage, hemorrhage
and thermal damage to surrounding
tissues. After one week,
there is normal epidermis
and dermis, demonstrating
clearly the superiority
of PDL over CW treatment
in port wine stain. PDL
is best for lesions in
lips, neck and eyelids
that have thin skin. Deep
penetrating longer wave
lengths like, yellow light
may be needed for lesions
located deep.
Local anesthesia may or
may not be needed for PDL
treatment. Infants and
children need sedation
and general anesthesia.
Problems in PDL treatment
occur when melanin in heavily
pigmented skins hinder
absorption by deeper vascular
structures, increasing
risks.
A study on 500 vascular
lesions patients, found
persistent atrophic scars
in less than 0.1%. Permanent
hyperpigmentation occurred
in 1%, transient hypopigmentation
in 2.6% and transient dermatitis
in less than 1%. Others
found hyperpigmentation
at 10% to 15%, mostly in
dark skinned patients.
Hyperpigmentation slowly
cleared in 6 months. Retinal
damage and superficial
burns also occur.
Continuous
wave lasers
Continuous wave (CW) lasers
use wave lengths from 488nm
to 578nm.
At
577nm wave length and above
they have the greatest
penetration and high selective
hemoglobin absorption over
melanin. CW lasers cause
more thermal damage, compared
to pulsed lasers, because
the exposure time is inherently
not specific to the thermal
relaxation time of the
target.
CW lasers are often effective
for small lesions, especially
a type of port wine stains
that have mature more deeply
pigmented blue purple lesions.
Anesthesia is needed when
port wine stains are treated
with CW laser. Depigmentation
can be a problem with CW
lasers since most work
at 532nm and lower range,
where melanin absorption
is more.
Types of continuous wave
lasers
Argon laser: This was
the first vascular specific
CW laser and was the standard
for many years. The medium
is argon. Currently it
is used for large blood
vessels. The penetration
is limited to 1mm, therefore
suitable only for superficial
lesions. Side effects include
crusting that cures in
10 days, scarring, pigment
alterations in dark skins,
skin texture changes and
hypopigmentation. Some
consider argon laser superior
to PDL for treating port
wine stains.
Argon-pumped tunable dye
laser (APTDL): This CW
laser uses a shuttering
mechanism to deliver 30
seconds pulsed lasers.
While it can work at a
broad range of wave lengths,
currently it is designed
for two wave length settings
of 577nm and 585nm. Because
it has a small spot size,
the fluence can be very
high. Its performance has
reportedly been better
than argon laser and comparable
to PDL in some cases. Blood
vessels of sizes large
and small can be treated
with this laser.
Benign vascular lesions
respond best to this laser.
Side effects include blanching
during treatment and erythema
and edema post-treatment.
Blistering is not uncommon.
Copper vapor laser: It
operates at 578nm wave
length with pulse duration
of 30 to 50 seconds. Excessive
thermal heating due to
large number of pulses
is avoided by using a shuttering
system that limits thermal
damage and scarring. Temporary
transient hyperpigmentation
occurs in 10% patients.
This method shows good
selective targeting of
port wine stains without
any damage to non-vascular
parts but is not as selective
in brown skins due to melanin.
There is necrosis of the
endothelial without vessel
rupture.
Potassium titanium phosphate
(KTP) laser: It is a pulsed
CW system similar to argon
laser. These are now being
widely used due to their
portability and lower costs.
Due to their large spot
sizes, vessels larger than
those treated by PDL can
be treated by this system.
There are cooling heads
to limit heating, scarring
and pigmentation.
Finally, PDL is more expensive
and needs more maintenance
than the CW system. CW
does not cause purpura,
while all PDLs cause purpura.
