Biomedical Engineering Reference
In-Depth Information
refl ects a diminished melanocyte content of the skin and corre-
lates with both the depth of resurfacing and the degree of ther-
mal injury. These patients generally have long-lasting erythema,
often have had problems with milia and acne as well, and may
have areas of scarring. These patients typically have been treated
with free-hand techniques allowing pulse stacking or with CPG
patterns having greater than 50% overlap. These patients often
have received more than three laser passes as well.
Treatment of hypopigmentation has been diffi cult, includ-
ing the use of PUVA, excimer laser, or UVB fl ashlamps. When
segmental hypopigmentation or pseudohypopigmentation is
present, resurfacing the remainder of the face will blend the
area and decrease its visibility (Fig. 6.30). An incidence of
about 20% has been reported for hypopigmentation, but this
must be examined carefully and pseudohypopigmentation
separated as a different phenomenon, because it may not be
preventable. In a review of 104 patients 1-4 years postopera-
tively, we found hypopigmentation in 19.2% (20 of 104). Pseu-
dohypopigmentation was present in 65% of these patients and
true hypopigmentation in 35%. Hypopigmentation was classi-
fi ed as mild in 85% of these patients. When examined more
closely, these 20 patients with hypopigmentation were also the
patients having the worst photodamage preoperatively, those
with the most signifi cant clinical improvement, and those who
were most pleased with their results. Pseudohypopigmenta-
tion should be viewed as a consequence of resurfacing in sig-
nifi cantly photodamaged skin rather than a complication.
However, patients should be forewarned of this aspect of the
procedure.
Scarring
Erythematous and hypertrophic scars often result from exces-
sive depth of tissue injury. This is usually caused by excess tissue
heating and residual thermal damage well beyond the depth of
tissue vaporized by the laser. Incorrect “off ” times, high scanner
densities (greater than 40%), and failure to keep the handpiece
moving during resurfacing are some of the treatment methods
that lead to inadvertent overlap or “stacking” of pulses, with the
resultant accumulation of heat and residual thermal damage.
Scarring is also seen more frequently in patients who develop
a postoperative infection, particularly in those who have had
multiple prior surgical procedures, altering the anatomy of the
region. In addition, patients treated more aggressively, result-
ing in a thicker layer of thermal necrosis, may be more prone
to infection. Careful preoperative history taking to rule out
predisposing factors and immediate treatment of postopera-
tive infections are mandatory.
Scarring is much more frequently seen in treatment of nonfa-
cial areas, such as the neck. Decreased adnexal structures, thinner
dermis, and increased tissue tension and traction secondary to
motion are predisposing factors. In a trial of 10 patients receiving
a single-laser pass of 300 mJ with a CPG density of 6, we encoun-
tered scarring of the lower one-third of the neck in three patients
and patchy hypopigmentation in four patients (Fig. 6.34).
The earliest evidence for the development of a scar is usually
erythema and pruritus. At this point, the affected area should be
cultured to rule out infection, and topical high-potency cortico-
steroids should be applied two or three times daily. If the affected
area begins to thicken, intralesional injection of triamcinolone
(10 mg/mL) with 5-fl uorouracil (50 mg/mL) in a 1:9 dilution
(1-mg triamcinolone with 45-mg 5-fl uorouracil) should begin
every 2-3 days. Topical silicone dressings should also be applied.
If further progression occurs, we advise using the 585-nm fl ash-
lamp pumped pulse dye laser (PDL) or other vascular lasers or
intense pulsed light (IPL) every 4 weeks. With these techniques,
permanent scarring has been avoided (Fig. 6.35).
Petechiae
Although of almost no long-term signifi cance, the appearance
of small petechiae is often a source of much concern to the
patient. They appear just as reepithelialization is complete,
confl icting with the patient's desire to return to public view.
Small subepithelial hemorrhages from the immature base-
ment membrane and undeveloped rete appear to be the cause.
These factors render the skin more fragile and easily damaged
with minor trauma from rubbing or scratching. Petechiae may
continue for several weeks after the procedure but clear quickly
without treatment.
Ectropion
Contraction of previously scarred tissue of the lower eyelid
leads to excessive tightening and exposure of the conjunctiva.
This avoidable complication usually occurs in patients who
(
A
)
(
B
)
(
C
)
Figure 6.34
(
A
)
Pseudomonas
infection developed on day 8 after single-pass laser resurfacing, resulting in nonhealing erosions on lower cheek. (
B
) Although this
area initially healed very well, at 4 months an obvious hypertrophic scar was developing, corresponding to site of infection. (
C
) Intensive treatment with intrale-
sional 5-fl uorouracil (45 mg/mL) and triamcinolone (Kenalog, 1 mg/mL) followed by pulsed dye laser (6 J/cm
2
) resulted in scar resolution after approximately
1 year.
